CN1768442A

CN1768442A - Novel vanadium halide redox flow battery

Info

Publication number: CN1768442A
Application number: CNA2004800069798A
Authority: CN
Inventors: M·卡扎克斯; M·斯凯立斯-卡扎克斯; N·卡扎克斯
Original assignee: NewSouth Innovations Pty Ltd
Current assignee: NewSouth Innovations Pty Ltd; Unisearch Ltd
Priority date: 2003-03-14
Filing date: 2004-03-15
Publication date: 2006-05-03
Anticipated expiration: 2024-03-15
Also published as: ZA200507835B; AU2003901183A0; CN100521348C

Abstract

A prior to charge vanadium halide redox cell, a vanadium halide redox cell which is at a state of charge selected from the group consisting of a zero state of charge and a near zero state of charge and vanadium halide redox cell which are fully charged and partially charged are described. The prior to charge vanadium halide redox cell comprises a positive half cell containing a positive half cell solution comprising a halide electrolyte, vanadium (III) halide and vanadium (IV) halide, a negative half cell containing a negative half cell solution comprising a halide electrolyte, vanadium (III) halide and vanadium (N) halide wherein the amounts of vanadium (III) halide, vanadium (IV) halide and halide ions in the positive and negative half cell solutions are such that in a first charging step comprising charging the prior to charge vanadium halide redox cell, a vanadium halide redox cell having a state of charge selected from the group consisting of a zero state of charge and a near zero state of charge comprising predominantly vanadium (N) halide in the positive half cell solution and predominantly V(III) halide in the negative half cell solution can be prepared. The vanadium halide redox cell which is at a state of charge selected from the group consisting of a zero state of charge and a near zero state of charge comprises a positive half cell containing a positive half cell solution comprising a halide electrolyte and a vanadium halide which is predominantly vanadium (N) halide, a negative half cell containing a negative half cell solution comprising a halide electrolyte and a vanadium halide which is predominantly vanadium (III) halide wherein the amount of vanadium (N) halide in the positive half cell solution and the amount of vanadium (III) halide in the negative half cell solution are such that the vanadium halide redox cell is at a state of charge selected from the group consisting of a zero state of charge and a near zero state of charge.

Description

Novel vanadium halide redox flow battery

Technical Field

A vanadium halide redox flow battery is disclosed that employs a 50: 50 vanadium (III)/(IV) halide solution as the initial feed electrolyte solution in the positive and negative half-cells. The present invention also discloses a 50: 50 halogenated V (III)/V (IV) feed solution for use in positive and negative half-cells of a vanadium halide redox flow battery. A vanadium halide redox flow battery is also disclosed, wherein the initial feeding solution of the negative half-cell is a vanadium (III) halide electrolyte and the vanadium (IV) halide electrolyte is used as the feeding solution of the positive half-cell. Methods of producing halogenated vanadium (III), vanadium (IV), vanadium (III)/(IV) electrolytes for use in vanadium halide redox flow batteries are also disclosed. Further, methods of generating electricity by discharging a fully or partially charged vanadium halide redox flow battery or battery pack and methods of recharging a discharged or partially discharged vanadium halide redox flow battery or battery pack are also disclosed.

Also disclosed is a high energy density vanadium halide redox flow battery employing a 2: 1 ratio of vanadium (III) halide to vanadium (IV) halide in the initial feed electrolyte solution of the positive and negative half-cells, wherein the amount of positive half-cell solution is half that of the negative half-cell solution. Also disclosed is a high energy density vanadium halide redox flow battery wherein the initial feeding solution of the negative half-cell is a vanadium (III) halide electrolyte and the initial feeding solution of the positive half-cell is a 50: 50 vanadium (III) halide/vanadium (IV) electrolyte, wherein the amount of positive half-cell electrolyte is half of the amount of negative half-cell electrolyte. Methods of producing high energy density vanadium (III)/(IV) halide electrolytes for vanadium halide redox flow batteries are also disclosed.

Fixed or gelled electrolytes vanadium halide redox cells and methods of fixing electrolytes for vanadium halide redox cells are also disclosed. In addition, methods of generating electricity by discharging a fully or partially charged vanadium halide redox flow or battery or a gel electrolyte battery or battery and methods of recharging a discharged or partially discharged vanadium halide redox flow or battery or a fixed redox cell or battery are disclosed.

Background

In fact, it was determined that the energy density of a redox flow battery is the concentration of redox ions in solution, and therefore, during discharge of each mole of active redox ions, the battery voltage and the number of electrons change. In the case of all-vanadium redox flow batteries, the maximum vanadium ion concentration that can be used for wide temperature range operation is typically 2M or less than 2M. This concentration represents the solubility limit of the v (ii) and/or v (iii) ions in the sulphuric acid supporting electrolyte at temperatures below 5 ℃ and the stability of the v (v) ions at temperatures above 40 ℃.

A fully brominated Vanadium Redox Cell is disclosed in Australian patent application PS1921 "Vanadium bromine Redox Flow Battery" and PCT application PCT/GB2003/001757 "Metal bromine Redox Flow Cell" which uses a Vanadium (IV) Bromide solution in both halves. This system involves the use of a hydrogen bromide (HBr)/hydrogen chloride (HCl) mixture containing 0.1 to 5M vanadium (IV) bromide in the positive and negative half-cell electrolytes, thus overcoming cross-contamination of the two half-cell solutions. In this system, the solubility of brominated v (ii) and v (iii) is higher, so that higher energy densities are obtained than vanadium sulfate-based redox flow batteries.

In Australian patent application PS1921, "variable bromine Redox Flow Battery" and PCT application PCT/GB2003/001757, "Metal bromine Redox Flow Cell", equal amounts of brominated V (IV) solution are used in both half cells. In these patents, it is proposed that in an initial charge cycle, the V (IV) ions are first oxidized to V (V), followed by Br in the positive half-cell^-Oxidation to Br₃ ^-Or Br₂Cl^-While reducing V (IV) to V by 2-electron treatment in the negative half-cell²⁺. Followed by a charge-discharge cycle included in1-Electron V in negative half-cell²⁺/V³⁺Oxidation-reduction reaction and Br in positive half cell^-/Br₃ ^-And (4) carrying out oxidation-reduction reaction.

However, further studies by the inventors have shown that: in the presence of the high bromide ion concentration required to stabilize the bromine produced at the positive electrode, V (iv) is not oxidized to V (V) to any appreciable extent, and therefore, during the initial charge cycle, at the negative electrode, positive electrolyte must be directed to be reduced to V²⁺Per mole of V (IV) with two moles of Br^-Oxidation of the ions. Similarly, upon discharge, V is reduced by 1-electron reduction treatment²⁺Ion oxidation to V³⁺Thus, only half of the bromine formed is converted back to the original Br during the discharge cycle^-Form (a). This means that the positive half-cell electrolyte always contains either excess bromine or relatively unstable Br₃ ^-Or Br₂Cl^-A component that may cause problems with bromine gas evolution during operation of the vanadium bromide battery. In addition, the presence of excess bromine in the positive half-cell electrolyte increases the corrosion characteristics of this solution, thereby reducing the life of the cell assembly.

It is therefore desirable to modify the composition of the feed electrolyte of vanadium halide redox flow batteries to avoid excessive bromine generation during battery operation. And it is desirable to modify the electrolyte generation process so as to avoid the generation of excess bromine during electrolyte preparation.

The inventors also disclose: the amount of positive half-cell solution is halved by further adjusting the composition of the initial feeding solution of the two half-cells of the vanadium halide redox cell while still obtaining the same capacity in the cycle. This will allow a 25% reduction in the amount and weight of electrolyte and therefore an increase in the energy density and specific energy of the vanadium halide system of up to 25%, providing important benefits especially for mobile applications.

The inventors have also found that: the generated bromine can be stabilized by complexing, fixing or gelling the vanadium halide battery electrolyte, so that a greater part of the bromide ions can be oxidized without significant bromine loss during the charging of the positive half-cell electrolyte.

Disclosure of Invention

According to a first aspect of the present invention there is provided a vanadium halide redox cell prior to charging comprising;

a positive half-cell having a positive half-cell solution comprising a halogenated electrolyte, vanadium (III) halide, and vanadium (IV) halide;

a negative half-cell having a negative half-cell solution comprising a halogenated electrolyte, vanadium (III) halide, and vanadium (IV) halide;

wherein the amounts of vanadium (III) halide, vanadium (IV) halide and vanadium ions in the positive and negative half-cell solutions are such that:

so that in a first charging step comprising charging the vanadium halide redox cell prior to charging, a vanadium halide redox cell can be prepared having a state of charge selected from the group consisting of a zero state of charge and a state of charge close to zero, the cell comprising predominantly vanadium (IV) halide in the positive half-cell solution and predominantly vanadium (iii) halide in the negative half-cell solution.

Predominantly can be considered to mean that the total vanadium ion concentration of 100 mole% or in a particular solution is between 80% and 100%, 85% and 100%, 90% and 100%, 93% and 100%, 95% and 100%, 97% and 100%, 98% and 100%, or 99% and 100%.

The positive half-cell may include a positive electrode and the negative half-cell may include a negative electrode. The redox cell may include an ionically conductive separator disposed between the positive and negative half-cells and in contact with the positive and negative half-cell solutions. The ionically conductive separator may be a membrane or other suitable separator.

The amounts of vanadium (III) halide, vanadium (IV) halide and halide ions in the positive and negative half-cell solutions prior to charging the vanadium halide redox cell may be such that:

so that in the second charging step comprising charging the vanadium halide redox cell in a zero state of charge, a charged vanadium halide redox cell comprising the polyhalide complex in the positive half-cell solution and vanadium (III) halide in the negative half-cell solution can be prepared.

The positive half-cell solution may include vanadium (III) halide and vanadium (IV) halide in a halide electrolyte, wherein the molar ratio of V (III) to V (IV) is from about 0.9: 1 to about 6: 1, the negative half-cell solution includes vanadium (III) halide and vanadium (IV) halide, wherein the molar ratio of V (III) to V (IV) is from about 0.8: 1 to 6: 1, or from 0.9: 1 to about 6: 1, or from about 0.95: 1 to about 6: 1, or from about 0.98: 1 to about 6: 1, or from about 0.99: 1 to about 6: 1, or from about 1.1: 1 to about 6: 1, or from about 1.01: 1 to about 6: 1, or from about 1.02: 1 to about 6: 1, or from about 1.03: 1 to about 6: 1, or from about 1.04: 1 to about 6: 1, or from about 1: 1, or from about 1.5: 1 to about 6: 1, or from about 1.75: 1 to about 6: 1, or from about 2.1: 1 to about 6: 1, or from about 2.25: 1 to about 6: 1, or from about 2.5: 1 to about 6: 1, or from about 0.9: 1 to about 5.5: 1, or from about 0.9: 1 to about 5: 1, or from about 0.9: 1 to about 4.75: 1, or from about 0.9: 1 to about 4.5: 1, or from about 0.9: 1 to about 4: 1, or from about 0.9: 1 to about 3.75: 1, or from about 0.8: 1 to about 3.5: 1, or from about 0.9: 1 to about 3: 1, or from about 0.8: 1 to about 3: 1, or from about 0.9: 1 to about 3: 1, or from about 0.8: 1 to about 1, or from about 1 to about 2: 1, or from about 0.9: 1 to about 3: 1, or from about 1 to about 1, or from about 1.1: 1 to about 2: 1, and the amount of negative half-cell solution to the amount of positive half-cell solution may be equal to or about equal to the molar ratio of V (III) to V (IV).

The molar ratio of V (III) to V (IV) may beabout 1: 1, and the amount of negative half-cell solution to the amount of positive half-cell solution may be about 1: 1.

The molar ratio of V (III) to V (IV) may be about 2: 1, and the amount of negative half-cell solution to the amount of positive half-cell solution may be about 2: 1.

The halide may be selected from the group consisting of bromide and combinations of bromide and chloride.

The total halide ion concentration may be at least 3 times the total vanadium ion concentration. The concentration of total chloride ions may be 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or 10.5 times the concentration of total vanadium ions. The total chloride ion concentration may be in the range of 3-10.5, or 3-10, or 3-9, or 3-8, or 3-7, or 3-6, or 3-5, or 3-4 times the total vanadium ion concentration.

The halide may be selected from the group consisting of bromide and a combination of bromide and chloride, wherein the concentration of bromide ions is greater than the concentration of chloride ions and the total concentration of halide ions is at least 3 times the total concentration of vanadium ions.

According to a second aspect of the present invention there is provided a vanadium halide redox cell in a state selected from the group consisting of a zero state of charge and a near zero state of charge, the vanadium halide redox cell comprising:

a positive half-cell having a positive half-cell solution comprising a halogenated electrolyte and a vanadium halide, the vanadium halide comprising primarily vanadium (IV) halide;

a negative half-cell having a negative half-cell solution comprising a halogenated electrolyte and a vanadium halide, the vanadium halide comprising primarily vanadium (III) halide;

wherein the amount of vanadium (IV) halide in the positive half-cell solution and the amount of vanadium (III) halide in the negative half-cell solution are such that the vanadium halide redox cell is in a state of charge selected from the group consisting of a zero state of charge and a state of charge close to zero.

Charge states close to zero include charge states between the range of + 20% and-20%, + 15% and-15%, + 10% and-10%, + 5% and-5%, + 3% and-3%, + 2% and-2%, + 1% and-1% of the zero charge state.

The positive half-cell solution may not include a significant amount of polyhalide complex at and near zero state of charge.

According to a third aspect of the invention there is provided a fully charged vanadium halide redox cell comprising:

a positive half-cell having a positive half-cell solution comprising a halogenated electrolyte, a polyhalide complex, vanadium (IV) halide, and vanadium (V) halide;

a negative half-cell having a negative half-cell solution comprising a halogenated electrolyte and vanadium (II) halide;

wherein the molar concentration of vanadium (V) and polyhalide complex to the molar concentration of vanadium (II) halide is about stoichiometrically balanced.

According to a fourth aspect of the invention there is provided a partially charged vanadium halide redox cell comprising:

a negative half-cell having a negative half-cell solution comprising a halogenated electrolyte, vanadium (II) halide, and vanadium (III) halide;

wherein the moles of polyhalide complex and vanadium (V) to the moles of vanadium (II)halide are approximately stoichiometrically balanced.

In the third and fourth aspects, the number of moles of polyhalide complex to moles of vanadium (II) halide is about 1: 2.

In the third and fourth aspects, the moles of polyhalide complex to moles of vanadium (II) halide may be in the range of about 0.7: 2 to about 1.3: 2.

In the third and fourth aspects, the polyhalide complex forms a halide/polyhalide redox couple. The halide/polyhalide redox couple may be Br₃ ^-/Br^-、ClBr₂/Br^-Or BrCl₂ ^-/Cl^-And the like. Further examples of halide/polyhalide redox couples are described in PCT/AU02/01157 which is incorporated herein by cross-reference.

In the first to fourth aspects, the halide may be selected from the group consisting of bromide and a combination of bromide and chloride.

In the first to fourth aspects, the total halogen ion concentration may be at least 3 times the total vanadium ion concentration. The total halide ion concentration may be 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or 10.5 times the total vanadium ion concentration. The total halide ion concentration may be in the range of 3-10.5, or 3-10, or 3-9, or 3-8, or 3-7, or 3-6, or 3-5, or 3-4 times the total vanadium ion concentration.

In the first to fourth aspects, the halide may be selected from the group consisting of bromide and a combination of bromide and chloride, wherein the concentration of bromide ions is greater than the concentration of chloride ions, and wherein the concentration of total halide ions is at least 3 times the concentration of total vanadium ions.

In the first to fourth aspects, the positive half cell may include a positive electrode, and the negative half cell may include a negative electrode. The positive electrode is in contact with the positive half-cell solution and the negative electrode is in contact with the negative half-cell solution. The redox cell can include an ionically conductive separator disposed between and in contact with the positive half cell solution and the negative half cell solution. The ionically conductive separator may be a membrane or other suitable separator.

In the first to fourth aspects, the redox cell may be operated in a wide temperature range, for example in one of the following temperature ranges: -10 to 99, 0 to 99, 1 to 99, 5 to 95, 5 to 90, 5 to 75, 5 to 70, 5 to 65, 5 to 60, 5 to 55, 5 to 50, 5 to 45, 0 to 45, -10 to 45, 5 to 40, 0 to 40, -10 to 40, 5 to 35, 0 to 35, -10 to 35, 5 to 30, 0 to 30, 5 to 25, 5 to 20, 10 to 50, 15 to 50, 18 to 50, 15 to 40, 15 to 35 degrees celsius.

In the first to fourth aspects, the halide electrolyte may further include a complexing agent for bromine generated during charging.

In the first to fourth aspects, the halide electrolyte may be fixed or colloidal. Fumed silica is a suitable fixing or gelling agent.

In the first to fourth aspects, the redox cell may be a stirred or rocking type redox cell or a stationary redox cell or a flow redox cell or other suitable redox cell, such as a stationary redox cell or a gel redox cell or other redox cell. The term redox cell throughout the specification may also refer to a redox battery.

According to a fifth aspect of the present invention there is provided a method of producing an electrolyte for a vanadium halide redox cell, comprising:

the V (III) compound and the V (V) compound are dissolved in the HBr, LiBr, NaBr, KBr, or mixtures thereof in a molar ratio of about 3: 1 to produce a mixture of V (III) and V (V) ions in solution of about 50: 50. The compound of V (III) may be V₂O₃And the V (V) compound may be V₂O₅。

In one embodiment, a method of producing an electrolyte for a vanadium halide redox cell is provided that involves: the V (III) compound and V (V) compound are mixed in a molar ratio of about 3: 1 in solution HBr, NaBr, KBr, or mixtures thereof, and stirred until completely dissolved, thereby producing an about 50: 50 mixture of V (III) and V (V) ions. To avoid excess bromine generation, the V (III) compound is first added to the chloride solution and the V (III) compound is partially dissolved prior to the addition of the V (V) compound. The dissolution can be carried out at room temperature and in a temperature range from room temperature to the boiling point. The resulting solution was added approximately equally to the two half-cells of the vanadium halide redox cell prior to charging.

According to a sixth aspect of the present invention there is provided a method of producing an electrolyte for a vanadium halide redox cell, comprising:

equal moles of V (III) and V (IV) compounds are dissolved in HBr, LiBr, NaBr, KBr, or mixtures thereof in solution to produce an approximately 50: 50 ionic mixture of V (III) and V (IV) in solution.

The compound of V (III) may be V₂O₃And the V (IV) compound may be V₂O₄。

The solution may also contain chloride ions.

According to a seventh aspect of the present invention there is provided a method of producing an electrolyte for a vanadium halide redox cell, comprising:

the V (III) compound and the V (V) compound are dissolved in a 4.5: 1 molar ratio in solution HBr, LiBr, NaBr, KBr or mixtures thereof to produce a 2: 1 ionic mixture of V (III) and V (IV).

The compound of V (III) may be V₂O₃And the V (V) compound may be V₂O₅. To avoid excess bromine generation, the compound v (iii) is first added to the halide solution and partially dissolved prior to the addition of the compound v (v). The dissolution may be carried out at room temperature or in a temperature range from room temperature to the boiling point. The resulting solution was added to both half-cells of the vanadium halide redox cell prior to charging, with the ratio of positive half-cell solution to negative half-cell solution being approximately 1: 2.

According to an eighth aspect of the present invention there is provided a method of producing an electrolyte for a vanadium halide redox cell, comprising:

the V (III) and V (IV) compounds are dissolved in a 2: 1 molar ratio in solution HBr, LiBr, NaBr, KBr or mixtures thereof to produce a 2: 1 ionic mixture of V (III) and V (IV).

In the fifth to eighth aspects of the present invention, the total vanadium ion concentration may be between 0.5 and 5M, between 0.75 and 5M, between 1 and 5M, between 1.25 and 5M, between 1.5 and 5M, between 1.75 and 5M, between 1.9 and 5M, between 2 and 5M, between 2.1 and 5M, between 2.25 and 5M, between 2.3 and 5M, between 2.4 and 5M, between 2.5 and 5M, between 2.7 and 5M, between 3 and 5M, between 3.5 and 5M, between 4 and 5M, between 1 and 4.5M, between 1 and 4M, between 1 and 3.5M, between 1 and 3M, between 1 and 2.75M, between 1 and 2.5M, between 1 and 2.25M, between 1 and 2M, between 1.8 and 2.75M, between 1.8 and 2.5M, between 1.8 and 2.4M, between 1.8 and 2.3M, between 1.8 and 2.2M or between 1.9 and 2.1M, and the total bromide concentration may be between 2 and 12M. Bromide ions or a mixture of bromide and chloride ions may be present. The total halide ion concentration (which may be bromide or a mixture of bromide and chloride) is at least 3 times the total vanadium ion concentration. In the presence of a mixture of bromide and chloride ions, the bromide ion concentration is greater than the chloride ion concentration.

The electrolyte may be HBr, and the total bromide concentration may be 2 to 12M.

The electrolyte may further contain chloride ions at a concentration of 0.5 to 3M.

In one particular form of the invention, a vanadium (IV) bromide or vanadium (v) bromide/chloride redox flow battery (also referred to as a vanadium halide redox flow battery) is provided that employs a vanadium (III) bromide or vanadium (III) bromide/chloride solution in the negative half-cell and a vanadium (IV) bromide or vanadium (IV) bromide/chloride solution in the positive half-cell.

In both half-cells, a mixture of about 50: 50 vanadium (III) bromide to vanadium (IV) bromide may be used.

The negative half-cell electrolyte may also contain v (ii), v (iii) and/or v (iv) ions in a supporting electrolyte of HBr, NaBr, KBr or mixtures thereof, and the positive electrolyte contains a bromide/polyhalide pair in the presence of v (iv) and/or v (v) ions.

The charged or partially charged negative half-cell electrolyte may comprise VBr in a supporting electrolyte₂And/or VBr₃The supporting electrolyte is selected from the group consisting of HBr, LiBr, NaBr, KBr, HCl, NaCl, KCl, or a mixture thereof.

The negative half-cell electrolyte solution can include 0.5 to 5M VBr in 0.1 to 10M HBr or HCl/HBr or NaCl/HBr or KCl/HBr mixture₃And/or VBr₂。

Charged or partially chargedpositive half-cell electrolyteMay contain from Br^-/Br₃ ^-、Br^-/BrCl₂ ^-、Br^-/Br₂Cl^-Or a mixture thereof.

The positive half-cell electrolyte solution may include Cl at a total concentration of 1 to 12M^-And Br^-Vanadium ions in the mixture.

The positive half-cell electrolyte may comprise vanadium ions in a solution containing 0.5 to 5M polyhalide ions, such as Br₃ ^-Or Br₂Cl^-Ions or mixtures thereof, etc. (a more detailed list of polyhalo-ions, particularly polybromo-ions, polychlorides and polybromo/polychlorides is found in PCT/AU02/01157, which is incorporated herein by reference).

The redox flow battery may include a negative half-cell that may include a v (iii) and/or v (iv) ionic solution in a supporting electrolyte selected from the group consisting of HBr, NaBr, KBr, or mixtures thereof, and a positive half-cell having a v (iv) and/or v (v) ionic solution in a supporting electrolyte selected from the group consisting of HBr, NaBr, KBr, or mixtures thereof.

The positive and negative half-cell electrolytes may also contain chloride ions at a concentration of 0.1 to 5M.

The partially charged negative half-cell electrolyte solution of the vanadium halide redox flow battery can include 0.5 to 5M VBr in a supporting solution of HBr, NaBr, KBr, or mixtures thereof₂And/or VBr₃。

The negative half-cell electrolyte solution may further include Cl at a concentration of 0.1 to 5M^-Ions.

In the negative half-cell electrolyte, the concentration range of excess bromide and chloride ions may be selected from the group consisting of 0.1 to 10M and 0.1 to 5M.

The discharging or partially charging positive half-cell electrolyte solution of the vanadium halide redox flow battery may include v (iv) and/or v (v) ions in a supporting solution of HBr, NaBr, KBr, or mixtures thereof.

The positive half-cell electrolyte solution may also contain 0.5 to 5M vanadium ions in a mixture of 0.5 to 12M bromide and chloride ions.

In another form, there is provided a method of producing an electrolyte for a vanadium halide redox flow battery, comprising: equimolar amounts of V (III) and V (IV) compounds are mixed in solution with HBr, NaBr, KBr or a mixture thereof and stirred until the solution is complete, producing an approximately 50: 50 ionic mixture of V (III) and V (IV).

The solution may also contain chloride ions. The total bromide ion concentration may be greater than the total chloride ion concentration.

In yet another form, a high energy density vanadium halide redox flow battery is provided that employs an initial feed solution of vanadium (III) bromide and vanadium (IV) bromide in a molar ratio of about 2: 1 in both half-cells, wherein the amount of positive half-cell electrolyte is about equal to the amount of negative half-cell electrolyte.

In another form, there is provided a method of producing electrolyte for a high energy vanadium bromide redox flow battery, comprising: v (III) and V (V) compounds in a 4.5: 1 molar ratio are mixed in a solution of HBr, NaBr, KBr, or a mixture thereof and stirred until the solution is complete, thereby producing an approximately 2: 1 mixture of V (III) and V (IV) ions.

The compound of V (III) may be V₂O₃And the V (V) compound may be V₂O₅. To avoid excess bromine generation, the compound v (iii) is first added to the halide solution and partially dissolved prior to the addition of the compound v (iii). The solution may be carried out at room temperature or at a temperature ranging from room temperature to the boiling point or from room temperature to 80 ℃.

In a further form, there is provided a method of producing an electrolyte for a vanadium halide redox flow battery, involving: the V (III) and V (IV) compounds are mixed in a 2: 1 molar ratio in solution with HBr, NaBr, KBr, or a mixture thereof and stirred until the solution is complete, producing an approximately 2: 1 mixture of V (III) and V (IV) ions.

The total vanadium ion concentration may be between 0.5 and 5M and the halide may be bromide or bromide/halide, and the total bromide or bromide/chloride concentration may be between 2 and 12M.

The supporting electrolyte may be HBr, and the total bromide concentration may be 8 to 12M.

The solution may also contain chloride ions at a concentration of 0.5 to 3M.

In a ninth aspect of the present invention, there is provided a process of partially charging the vanadium halide redox cell before charging in the first aspect, comprising: and providing electrical energy to the positive electrode in the positive half cell and the negative electrode in the negative half cell, thereby deriving trivalent vanadium ions from the negative half cell solution and tetravalent vanadium ions from the positive half cell solution.

After the partial charging process of the ninth aspect, the redox cell may be at a zero state of charge or a state of charge close to zero. Theelectrolyte in the redox cell after the partial charging treatment of the ninth aspect may not contain a polyhalide complex.

According to a tenth aspect of the present invention, there is provided a process of charging the vanadium halide redox battery before charging in the first aspect, comprising: electrical energy is provided to the positive electrode in the positive half cell and the negative electrode in the negative half cell to derive divalent vanadium ions from the negative half cell solution and to derive tetravalent vanadium ions, pentavalent vanadium ions and halide/polyhalide redox pairs in the positive half cell solution.

After the charging process of the tenth aspect, the redox cell may be partially charged or fully charged.

According to an eleventh aspect of the present invention, there is provided a process of charging the vanadium halide redox cell of the zero state of charge or close to zero state of charge in the second aspect, comprising: electrical energy is provided to the positive electrode in the positive half cell and the negative electrode in the negative half cell to derive divalent vanadium ions from the negative half cell solution and to derive tetravalent vanadium ions, pentavalent vanadium ions and halide/polyhalide redox pairs in the positive half cell solution.

After the charging process of the eleventh aspect, the redox cell may be partially charged or fully charged.

According to a twelfth aspect of the invention there is provided a process for charging the partially charged vanadium halide redox cell of the third aspect, comprising: electrical energy is provided to the positive electrode in the positive half cell and the negative electrode in the negative half cell to derive divalent vanadium ions from the negative half cell solution and to derive tetravalent vanadium ions, pentavalent vanadium ions and halide/polyhalide redox pairs in the positive half cell solution.

After the charging process of the twelfth aspect, the redox cell may be partially charged or fully charged.

The present invention provides a vanadium redox cell prepared from any one of the ninth to twelfth aspects.

According to a thirteenth aspect there is provided a process for generating electricity from a vanadium halide redox cell of the third or fourth aspects, the process comprising: electrical energy is drawn from the redox cell.

Drawing electrical energy may include electrically coupling an electrical load to a positive electrode of the positive half cell and to a negative electrode of the negative half cell.

According to a fourteenth aspect of the present invention there is provided a process for rebalancing the electrolyte of a vanadium halide redox cell of any one of the first to fourteenth aspects, comprising: the positive half cell solution is mixed with the negative half cell solution to form a mixed solution, and this mixed solution is placed in the positive half cell and the negative half cell.

The positive half-cell may be tightly isolated from air and the positive solution may be degassed. The positive half-cell may be degassed. The positive half-cell and positive solution may be degassed using nitrogen, argon, helium, or other suitable others.

The positive half-cell and the positive solution may be degassed with a non-oxygen containing gas. The negative half-cell may be tightly isolated from air and the negative solution may be degassed. The negative half-cell may be degassed. The negative half-cell and negative solution may be degassed with nitrogen, argon, helium, or other suitable gas. The negative half-cell and negative solution may be degassed with a non-oxygen containing gas.

According to a fifteenth aspect of the present invention there is provided a vanadium halide redox cell system comprising the vanadium halide redox cell of any one of the first to fourth aspects of the present invention and further comprising a positive solution reservoir, a positive solution supply and return line coupled between the positive solution reservoir and the positive half cell, a negative solution reservoir, a negative solution supply and return line coupled between the negative solution reservoir and the negative half cell and at least one pump in the at least one positive solution supply and return line and at least one pump in the at least one negative solution supply and return line.

The system of the fifteenth aspect may further comprise a charger electrically coupled to the positive electrode of the positive half cell and the negative electrode of the negative half cell. The charger may include a power source and a switch. The system of the fifteenth aspect may further comprise an electrical extraction circuit electrically coupled to the positive electrode of the positive half cell and the negative electrode of the negative half cell. The electrical extraction circuit may include a resistor and a switch.

The positive and negative electrodes may be graphite, carbon, glassy carbon, carbon fiber materials (e.g. non-woven fabric, type: CFT-3000 Ahlstroem, Finland), cellulosic carbon fabrics (e.g. GF-20, Nikon carbon company Limited, Japan), platinized titanium, Pt, Au, Pb, RuO₂E.g. TiO doping₂、RuO₂Or IrO₂A sterically stabilized anode (e.g., positive electrode), a conductive polymer coating, or other suitable electrode of the noble metal or combination thereof.

Detailed Description

In the wholeTheterm polyhalide complex or ion in the specification and claims is a complex or ion of three or more halogen atoms. The polyhalide complex being Br₃ ^-、ClBr₂ ^-And BrCl₂ ^-(see PCT/AU02/01157 incorporated herein by cross-reference for purposes of further illustration).

Throughout the specification, the terms electrolyte and supporting electrolyte are used interchangeably. The electrolyte used in the redox cell of the present invention is preferably an aqueous electrolyte.

50: 50 halogenation of V (IV) and V (III) in improved vanadium halide redox flow batteriesThe solution (referred to as V (3.5+)) serves as the initial feeding solution for the positive half-cell and the negative half-cell. Thus, in contrast to brominated redox flow batteries employing a brominated V (IV) feed solution, during initial charging of the modified cell, the V (III) and V (IV) ions in the negative half-cell are reduced to V according to the following reaction²⁺：

Initial charge reaction of the negative electrode:

whereas in the positive half-cell, the initial charge reaction is:

initial charge reaction of the positive electrode:

then:

or in the presence of bromide/chloride mixed with a supporting electrolyte:

or

The subsequent charge-discharge cycle thus comprises:

at the negative electrode:

and at the positive electrode:

or in the presence of bromide/chloride mixed with a supporting electrolyte:

thus, vanadium halide redox flow batteries and vanadium halide redox batteries employ 0.1 to 5M vanadium (III)/(IV) halide (e.g., vanadium (III) bromide)/(IV) or vanadium (III) bromide/chloride (IV) chloride) solutions in both half-cells. The concentration of vanadium halide (III)/(IV) in the two half-cells may be in the range of 0.1 to 4.5M, 0.1 to 4M, 0.1 to 3.5M, 0.1 to 3M, 0.1 to 2.5M, 0.1 to 2M, 0.1 to 1.9M, 0.1 to 1.75M, 0.1 to 1.5M, 0.1 to 1.25M, 0.1 to 1M, 0.5 to 5M, 1 to 5M, 1.5 to 5M, 1.75 to 5M, 1.9 to 5M, 2 to 5M, 2.25 to 5M, 2.5 to 5M, 2.75 to 5M, 3 to 5M, 3.5 to 5M, 4 to 5M, 4.5 to 5M, 1.75 to 4.5M, 1.75 to 4M, 1.75 to 3.5M, 1.75 to 5M, 1.5M, 1.75 to 5M, 2 to 5M, or 1.75 to 5M. For example, the vanadium halide (III)/(IV) concentration of the two half-cells may be about 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75 or 5M. A 0.1 to 5M solution of vanadium bromide or vanadium bromide/chloride in the supporting electrolyte HBr can be initially placed into the positive and negative half-cells, wherein the vanadium bromide or vanadiumbromide/chloride solution contains approximately 50% v (iii) and 50% v (iv) ions. For example, the electrolyte solution initially placed into the two half-cells of a vanadium halide redox cell may include 0.5 to 5M at 0.5 to 10MOr 0.5 to 5M HBr, or V (III)/V (IV) bromination/chlorination in a supporting electrolyte. The electrolyte solution may also contain chloride ions at a concentration of 0.1 to 5M, 0.5 to 2M in 0.5 to 10M HBr, LiBr, NaBr, KBr, or mixtures thereof. The concentration of chloride ions can be less than or equal to the electrolyte concentration of bromide ions (i.e., Cl if the electrolyte is aqueous HBr at a concentration of 5M)^-The concentration of the ions may be 5M (e.g., in the range of 0.05M to 5M, such as 0.1 to 2M, or 0.2 to 2M, or 0.5 to 2M, or 0.75 to 2M, or 1 to 2M, or 1.5 to 2M, or 1.75 to 2M, or 0.15 to 2.5M, or 0.15 to 3M, or 0.15 to 3.5M, etc.). The reason is that: in the presence of an excess of halide, bromide formed during charging or discharging of the cell forms, for example, ClBr in the electrolyte₂ ^-Or Br₃ ^-Rather than developing to bromide gas in large quantitiesAnd chlorine (which is formed when the concentration of chloride ions in the electrolyte is higher than the concentration of bromide ions) will not form a complex in the electrolyte, but rather will develop into a gas in a non-traditional form (as opposed to bromide complexes in solution) for containment or recycling (by reducing chlorine to chloride ions). When chloride ions are present, there will be a mixture of chloride, bromide, and chloride/bromide vanadium (III) and (IV) in the electrolyte.

In a separate embodiment, the initial feed solution for the positive half-cell is 0.5 to 5M of a halide v (IV) (e.g., vanadium (IV) bromide or vanadium (IV) chloride/bromide) in a supporting electrolyte of 0.5 to 5M HBr, while the initial feed solution for the negative half-cell contains 0.5 to 5M of a halide v (III) (e.g., vanadium (III) bromide or vanadium (III) chloride/bromide) in 0.5 to 5 MHBr. The electrolyte solution may also contain chloride ions at a concentration of 0.05 to 5M, 0.1 to 5M, or 0.5 to 2M in 0.5 to 10M HBr, LiBr, NaBr, KBr, or mixtures thereof. The total bromide ion concentration may be greater than the total chloride ion concentration.

In the case of a high energy density vanadium halide redox cell, since the amount of positive half cell solution is approximately equal to half the amount in the negative half cell, a 0.1 to 5M solution of vanadium halide (e.g., vanadium bromide or vanadium bromide/chloride) containing a ratio of about 2: 1V (iii) to V (iv), referring to V (3.33+), is initially placed in both half cells.

Before its fully discharged or charged state, the vanadium halide cell comprises a negative half-cell having a solution of V (III) and/or V (IV) ions in a supporting electrolyte and a positive half-cell having a solution of V (III) and/or V (IV) ions in a supporting electrolyte, wherein the supporting electrolyte of the negative half-cell is selected from the group consisting of: HBr, NaBr, KBr or mixtures thereof, the supporting electrolyte of the positive half-cell being selected from the group consisting of: HBr, LiBr, NaBr, KBr or mixtures thereof. The discharged positive and negative half-cell electrolytes may also contain chloride ions at a concentration in the range of 0.05 to 5.5M, 0.1 to 5M, or 0.5 to 2M. The total bromide ion concentration may be greater than the total chloride ion concentration.

In another embodiment of the present invention, a high energy density vanadium halide redox flow battery uses a 2: 1 mixture of brominated or brominated/chlorinated v (iii) and v (iv) solutions as the initial feed solutions for the positive and negative half-cells, with the amount of positive half-cell solution being half that of the negative half-cell solution. Thus, in contrast to vanadium bromide redox flow batteries employing equal amounts of V (IV) bromide or 50: 50V (III)/V (IV) feed solution on both sides, during initial charging of the battery containing equal amounts of a 2: 1 mixture of V (III)/V (IV) (referred to as V (3.33+)), the following reactions occur:

initial charge reaction of the negative electrode:

whereas in the positive half-cell, the initial charge reaction is:

initial charge reaction of the positive electrode:

then:

or in the presence of bromide/chloride mixed with a supporting electrolyte:

or

The subsequent charge-discharge cycle thus comprises:

at the negative electrode:

and at the positive electrode:

this shows that the vanadium ions of 1/3 in the negative half cell remain unreacted. However, when only half the amount of V (3.33+) solution is used on the positive side, all vanadium ions in the negative half-cell electrolyte will react during the charge-discharge cycle, and therefore, more bromide ions will be utilized in the positive half-cell.

Thus, a high energy density vanadium halide redox flow battery or redox cell may employ an initial feed solution of 0.1 to 5M vanadium (III)/(IV) halide in two half-cells, which may include v (III) to v (IV) ions in a supporting electrolyte HBr in a molar ratio of about 2: 1, with the amount used in the positive half-cell being equal to twice the amount used in the negative half-cell. The electrolyte solution initially placed into the two half-cells of the vanadium halide redox cell can include 0.5 to 3M of v (iii) bromide/IV or v (iii)/v (IV) bromide/chloride in a supporting electrolyte of, for example, 0.5 to 10M HBr or 0.5 to 5M HBr. The electrolyte solution may also contain chloride ions in a concentration of, for example, 0.1 to 5M or 0.5 to 2M in 0.5 to 10M HBr, LiBr, NaBr, KBr, or mixtures thereof. The total bromide ion concentration may be greater than the total chloride ion concentration.

The supporting electrolyte in each redox flow cell or redox cell can be HBr, NaBr, KBr, or mixtures thereof at concentrations ranging from 0.1 to 12M, or from 2 to 10M. HCl, LiCl, NaClAnd/or KCl may also be added to the electrolyte to form a stable polyhalide with the bromine formed in the positive half cell during charging. The concentration of bromide ions should be greater than the concentration of chloride ions. Vanadium halide redox flow batteries or negative and positive half-cell electrolytes of redox batteries can have concentrations of vanadium bromide (or vanadium bromide/chloride, where vanadium chloride/bromide refers to a mixture of vanadium chloride, vanadium bromide, and vanadium bromochloride that occurs when chloride and bromide ions are present) of 0.1 to 6M, but more typically from 0.5 to 5M or from 1 to 5M, and even more typically from 1 to 4M. Br in fully charged vanadium chloride redox flow battery or positivehalf cell of redox cell₃ ^-、Br₂Cl^-And/or Cl₂Br^-The concentration of the ions may be 0.1 to 5M, 0.5 to 5M, 1 to 3M, or 1 to 2M.

In the cycling of the cell, the electrolyte of the negative half-cell, in the presence of v (iv) and/or v (v) ions, comprises v (ii), v (iii) and/or v (iv) ions, and the positive electrolyte comprises a halogenated/polyhalogenated pair (e.g., a brominated/polyhalogenated pair). In circulation, the negative half-cell electrolyte may contain VBr in a supporting electrolyte₂And/or VBr₃Wherein the supporting electrolyte is selected from the group consisting of HBr, LiBr, NaBr, KBr, or mixtures thereof. The electrolyte may also include HCl, NaCl, KCl, or a mixture thereof. The negative half-cell electrolyte solution can include 0.5 to 5M VBr in 0.1 to 10M HBr or HCl/HBr or LiCl/HBr, NaCl/HBr, or KCl/HBr mixture₃And/or VBr₂. The concentration of bromide ions should be greater than the concentration of chloride ions.

A charged or partially charged positive half-cell of a vanadium halide redox flow battery or redox cell comprises an electrolyte solution of vanadium ions and one or more redox couples selected from the group consisting of: br^-/Br₃ ^-、Br^-/Br₂Cl^-Or mixtures thereof. In the discharged state, the vanadium halide redox flow battery or redox battery contains a positive half-cell electrolyte, wherein the positive half-cell electrolyte includes Br at a total concentration of 1 to 12M^-And Cl^-Vanadium ions in the mixture. The concentration of bromide ions should be greater than the concentration of chloride ions. In the charged or partially charged state, the positive half-cell electrolyte is included in a solution containing 0.5 to 5M Br₃ ^-Or Br₂Cl^-Ions or mixtures thereof.

The vanadium halide redox flow battery or partially charged negative half-cell electrolyte solution of the redox battery may include 0.5 to 5M VBr in a supporting electrolyte₂And/or VBr₃Wherein the supporting electrolyte is HBr, LiBr, NaBr, KBr or their mixture. Negative half-cell electrolyte solutionMay contain Cl at a concentration of 0.1 to 5M^-Ions. The excess bromide and chloride ion concentration in the negative half cell may be 0.1 to 10M or 0.1 to 5M. The concentration of bromide ions should be greater than the concentration of chloride ions.

The vanadium halide redox flow battery or partially charged positive half-cell electrolyte solution of the redox battery may include multiple halide couples + v (iv) and/or v (v) ions in a supporting electrolyte, wherein the supporting electrolyte is HBr, LiBr, NaBr, KBr or mixtures thereof. The positive half-cell electrolyte solution may contain 0.5 to 5M vanadium ions in a mixture of 0.5 to 12M bromide ions and chloride ions. The concentration of bromide ions may be greater than the concentration of chloride ions.

The feed electrolyte solution for both half-cells of a high energy density vanadium halide redox cell may comprise 0.5 to 5M vanadium bromide or bromide/chloride in a supporting electrolyte, wherein the supporting electrolyte is HBr, LiBr, NaBr, KBr or mixtures thereof, the molar ratio of the v (iii) and v (iv) ions of these vanadium bromide or bromide/chloride is 2: 1, the amount of positive half-cells being approximately equal to half the amount of negative half-cells. The ion ratio of V (III) and V (IV) in the feed solution may vary from 1.8: 1 to 2.2: 1, and the ratio of the amounts of negative electrolyte and positive electrolyte may also vary between 1.8: 1 and 2.2: 1. The electrolyte solution may also contain chloride ions at a concentration of 0.1 to 0.5M. The concentration of bromide ions may be greater than the concentration of chloride ions. The electrolyte solution may have an excess of bromide and chloride ions at a concentration of between 0.1 and 10M, or more specifically between 0.1 and 5M.

The supporting electrolyte may be HBr, LiBr, NaBr, KBr or mixtures thereof at concentrations ranging from 0.1 to 12M or from 2 to 10M. HCl, LiCl, NaCl, KCl can also be added to the supporting electrolyte to form a stable polyhalide with the bromine formed in the positive half-cell during charging. The concentration of bromide ions may be greater than the concentration of chloride ions. The concentration of vanadium bromide in the negative half-cell electrolyte and the positive half-cell electrolyte of the high energy density vanadium halide redox flow battery or redox cell may be, for example, 0.1 to 4M, 0.5 to 4M, l to 3.5M, or 1 to 3M. Br in fully charged vanadium halide redox flow battery or positive half cell of redox battery₃ ^-、Br₂Cl^-And/or Cl₂Br^-The concentration of the ions may be, for example, 0.1 to 5M, 0.5 to 4M, 1 to 3.5M, or 1 to 3M.

The electrolyte may also contain a suitable complexing agent to stabilize bromine or polyhalides produced during charging of the vanadium halide redox flow or redox cell. Complexing bromine with a suitable complexing agent such as polyethylene glycol, a tetraalkyl-ammonium halide such as 2-pyrrolidone, or a cyclic structure such as a pyran (pyrollidone) compound having a nitrogen atom in the ring structure will stabilize the bromine and enable oxidation of more bromide ions in solution during charging.

In a separate embodiment of the present invention, a gelled or immobilized vanadium halide redox cell is also disclosed. By immobilizing or gelling the vanadium halide battery electrolyte with a fixing or gelling agent, such as silica, fumed alumina, fumed titanium dioxide or polyacrylamide, the bromine produced can be stabilized so that a larger portion of the bromine ions can be oxidized during charging of the positive half-cell electrolyte.

The ion exchange membrane separates the two half-cell electrolytes or the flow battery, and prevents the two solutions from being injected into the battery or the battery stackAre mixed in large amounts. The ion exchange membrane may be a cation exchange membrane that will allow carrying of H depending on the composition supporting the electrolyte⁺、Li⁺、Na⁺And/or K⁺Charge transfer of the ions. If an anion exchange membrane is used, then H will pass through⁺、Br^-And/or Cl^-The ions undergo charge transfer. The ion exchange membrane may be a cation exchange membrane such as Gore-SelectP-03430 or other Gore-Select membrane, a Flemion membrane, a Selemion CMV membrane, or the like. Other suitable cation or anion exchange membranes may also be used, requiring good chemical stability in the vanadium bromide/bromine or vanadium chloride/bromine solutions, low resistivity and low permeability of vanadium and polybromide or polyhalide ions in the positive half-cell and vanadium ions in the negative half-cell electrolyte. Polybromides refer to complexes having three or more bromine atoms.

The negative and positive electrode materials of the vanadium halide redox flow or redox cell may be porous carbon or graphite, graphite felt, rough or cloth material on a glassy carbon or conductive plastic substrate. The positive electrode material may also be an oxide covered with a thin sheet of titanium metal or an expanded metal mesh. The titanium-based electrode will provide a longer stability against oxidation during charging of the positive half-cell solution. Batteries may be incorporated into battery stacks comprising bipolar electrodes comprising carbon, or graphite felt, rough or cloth material printed or thermally bonded on a metal plastic substrate comprising carbon filled with polyethylene, polypropylene or other thermoplastic polymers which may also be mixed with rubber materials to produce good mechanical properties. Vanadium halide redox flow or redox batteries can also be electrically contacted without the need to add conductive fillers to the plastic substrate by thermally bonding porous carbon or graphite felt to each side of a polyethylene, polypropylene or polymer sheet so that the conductive carbon or graphite felt fibers on each side of the insulating substrate are in contact with each other through the plastic sheet, thereby creating a bipolar electrode.

The two half-cell electrolytes are stored in external tanks and pumped through the cell stack when charging and discharging reactions occur. The electrolyte may be charged by connecting the battery or battery terminals to a suitable power source, and in the case of electric vehicle applications, may also be mechanically refueled by exchanging the discharged solution with a recharging solution at a refueling station.

To discharge the battery pack, the terminals of the stack are connected to a load and electricity is generated by a flow of electrons from the negative terminal to the positive terminal of the battery or battery stack when the circuit is closed. Charging and discharging can be accomplished by turning on the pump and recirculating the electrolyte through the external tank and cell stack, or turning off the pump so that the solution in the stack reacts by itself to discharge. The two solutions can be periodically re-mixed to produce the original V (3.5+) or in the case of a high energy density cell, the original V (3.33+) in both cells. This periodic mixing allows any chemical imbalance created by the transfer of ions through the membrane to be corrected, thereby restoring the capacity of the system. The periodic mixing may be complete or only partial.

In a separate embodiment, the negative half-cell feed solution comprises bromination v (iii) or bromination/chlorination v (iii) in a bromide or bromination/chloride supporting electrolyte, and the positive half-cell feed solution comprises bromination v (iv) or bromination/chlorination v (iii) in a bromination or bromination/chlorination supporting electrolyte. When these solutions were re-mixed to restore the system capacity, the same V (3.5+) or V (3.33+) electrolyte was produced as in the previous example.

In a separate embodiment of the invention, a method of producing a V (3.5+) or V (3.33+) halogenated electrolyte is described. A method of producing a V (3.5+) halogenated electrolyte may involve mixing a V (III) compound with a V (V) compound in a molar ratio of 3: 1 in a solution of HBr, LiBr, NaBr, KBr, or mixtures thereof, and stirring until completely dissolved, thereby producing an approximately 1: 1 mixture of V (III) and V (V) ions. For example, the V (III) compound may be V₂O₃The V (V) compound may be V₂O₅And the ratio of vanadium trioxide to vanadium pentoxide powderExamples may vary from 2.8: 1 to 3.2: 1. The solution may also contain chloride ions. The concentration of bromide ions may be greater than the concentration of chloride ions.

A method of producing a V (3.3+) electrolyte for a high energy density vanadium bromide redox cell may involve mixing a V (iii) compound with a V (V) compound in a molar ratio of about 4.5: 1 in a solution of HBr, LiBr, NaBr, KBr, or mixtures thereof, and stirring until completely dissolved to produce an about 2: 1 mixture of V (iii) and V (iv) ions. The compound of V (III) may be V₂O₃And the V (V) compound may be V₂O₅And the ratio of vanadium trioxide to vanadium pentoxide powder can vary from 4: 1 to 4.9: 1. The solution may also contain chloride ions. The concentration of bromide ions may be greater than the concentration of chloride ions.

The process for producing the electrolyte for a vanadium halide redox cell may also involve mixing the v (iii) compound with the v (iv) compound in a molar ratio of about 2: 1 in a solution of HBr, LiBr, NaBr, KBr or mixtures thereof, and stirring until completely dissolved to produce an about 2: 1 mixture of v (iii) and v (iv) ions. In this process, the V (III) compound may be V₂O₃And the V (IV) compound may be V₂O₄And V is₂O₃And V₂O₄Varies from 1.8: 1 to 2.2: 1. In each of the above processes, the total vanadium ion concentration may be between 0.5 and 5M, andthe total bromide ion concentration may be between 2 and 12M. The solution may also include chloride ions. The concentration of bromide ions may be greater than the concentration of chloride ions.

The supporting electrolyte may be HBr, and the total bromide concentration may be 8 to 12M. The supporting electrolyte may also contain chloride ions at a concentration in the range of 2.5 to 3M.

The powders may be mixed at an elevated temperature of greater than 40 ℃ for a period of 30 minutes or more until all of the powder is completely dissolved.

In a separate embodiment, 2-4M vanadium halide electrolyte may be gelled with 3-6 wt% fumed silica or other suitable gelling agent to produce a gelled or fixed electrolyte VBr redox cell that provides greater stability to bromine produced during charging. In this embodiment, all of the solution is stored in the stack and there is no external tank or pump.

Drawings

Fig. 1 illustrates the preparation and use of brominated V (3.5+) electrolytes as feed solutions for the positive and negative half-cells of a vanadium halide redox flow battery.

Fig. 2 shows the preparation and use of equal amounts of brominated V (3.33+) electrolyte as feed solutions for the positive and negative half-cells of a vanadium redox flow battery. Shows the V in the negative half-cell during discharge²⁺Incomplete reaction of the ions.

Figure 3 shows the effect of using half the amount of brominated V (3.33+) electrolyte in the positive half cell compared to the negative half cell. All V in the negative half cell²⁺The ions react during discharge and twice as many available bromide ions are reversibly oxidized and reduced in the positive half-cell during charge and discharge, respectively.

Figure 4 shows a vanadium bromide redox cell employing an ion exchange membrane (1) to separate the compartments of the negative half-cell and the positive half-cell. Each half cell includes a porous graphite felt or mat that is either a negative (3) flow-through electrode or a positive (2) flow-through electrode, each in electrical contact with an electrically conductive substrate or current collector (4 and 5). Negative and positive electrolyte half-cell solutions are stored in separate external reservoirs (6 and 7) and pumps 8 and 9 are used to draw electrolyte through the respective half-cell where the charge-discharge reaction takes place.

Figure 5 shows a stationary gelled electrolyte redox cell employing membrane (1) to separate the positive half cell and the negative half cell. Each half cell contained a graphite felt porous electrode filled with V (3.5+) vanadium bromide electrolyte, which also contained sufficient fumed silica to form gels in the negative (2) half cell graphite felt electrode and the positive (3) half cell graphite felt electrode when allowed to set. The graphite felt electrode is in electrical contact with a conductive substrate that serves as a current collector for the negative (4) and positive (5) half cells.

FIG. 6 shows the use of Br at 6M^-+2M Cl^-Initial charge and discharge curves for cells supporting a solution of 2M V (3.5+) in electrolyte as the feed electrolyte for the positive and negative half cells. Charge and discharge current 1Amp, electrode area 25cm². The initial charge time was 3.2 hours, and the initial discharge time was 2.2 hours.

FIG. 7 shows a plot of cell voltage versus time for charge-discharge cycles of a vanadium halide redox flow battery containing 60ml of 8M Br in each half cell^-+1.3M Cl^-3M vanadium containing solution. Electrode area 25cm²The charge and discharge current is 2 Amp.

FIG. 8 shows the use of 110ml of 8M Br^-As a typical charge and discharge curve for the feed solution of the two half-cells, the solution of 2M V (3.5+) in the supporting electrolyte of (a). Charge and discharge current 1Amp, electrode area 25cm²。

FIG. 9 is a plot of battery voltage versus time for charge-discharge cycles of a vanadium halide redox flow battery in which the positive half cell contains 55ml of a solution of 8M Br in the solution^-The feed solution initially contained 2M V (3.33+), and in the negative half cell contained 110ml of a solution of 8M Br in the solution^-Contains 2M V (3.33 +). Electrode area 25cm²The charge and discharge current is 1 Amp.

FIG. 10 shows a vanadium bromide static cell test containing 2M vanadium bromide (3.5+) electrolyte gelled with fumed silica.

Fig. 11A shows the charge-discharge curve of a V/Br cell containing 2M V (3.5+) in 8M HBr as the initial feed solution.

FIG. 11B shows the charge-discharge curve of a V/Br cell containing 75 vol% 2M V (3.5+) in 8M HBr +25 vol% polyethylene glycol as the initial feed solution.

FIG. 11C shows the charge-discharge curve of a V/Br cell containing 50 vol% 2M V (3.5+) in 8M HBr +50 vol% polyethylene glycol as the initial feed solution.

FIG. 12 depicts a vanadium halide redox system.

Mode of operation

A2-4M vanadium bromide solution comprising about 50% V (III) ions and 50% V (IV) ions is prepared by mixing vanadium trioxide and vanadium pentoxide powders in a 3: 1 molar ratio at a temperature above 60 deg.C (or within a range such as 60.5-100 deg.C, 62-99 deg.C, 65-95 deg.C, 70-90 deg.C, 70-85 deg.C, 70-80 deg.C or 60.5-85 deg.C) in 6-12M Br^-Or Br^-/Cl^-Support of the solutionIn the electrolyte and reacting them. The resultant V (III)/V (IV) electrolyte solutions are added equally to both sides of the vanadium halide redox flow battery or battery. In the initial charge of the cell, the vanadium bromide (III)/(IV) solution is reduced to produce 2-4M VBr in the negative half-cell₂Whereas in the positive half-cell, the V (III) ions are oxidized to V (IV) and/or V (V), and the bromide ions are oxidized to produce 1-2M Br₃ ^-Or ClBr₂ ^-。

High energy density vanadium halide redox flow batteries involve the use of 2-3M of V (III)/V (IV) solution in each half-cell, which comprises V (III) and V (IV) in about a 2: 1 molar ratio, so that the amount of negative half-cells is about twice that of positive half-cells. During initial charging of a high energy density vanadium bromide redox cell or battery, the vanadium bromide (III)/(IV) solution is reduced to produce 2-3M VBr in the negative half-cell₂Whereas in the positive half-cell, the V (III) ions are oxidized to V (III) and/or V (V), and the bromide ions are oxidized to produce 2-3M Br₃ ^-Or ClBr₂ ^-。

In the discharge of two cells, VBr in the negative half cell₂Is oxidized into VBr₃And in the positive half cell, Br₃ ^-Or ClBr₂ ^-The ions being reduced to Br^-Ions. The cell or stack of cells comprises carbon bonded to a plastic or conductive plastic sheet as substrate materialOr graphite felt electrodes, and the two half-cells are separated by an anion or cation exchange membrane. The membrane comprises Gore Selet P-03430 (cation exchange membrane from w.l.gore) or other cation exchange membranes. The electrodes may also comprise carbon or graphite felt or mat pressed against a glassy carbon or graphite foil substrate. The two half-cell electrolytes are stored in an external tank and pumped through the cell stack during the charging and discharging reactions taking place. The electrolyte may be charged by connecting the terminals of the battery or batteries to a suitable power source, but may also be mechanically refueled by exchanging the discharged solution with a recharging solution at a refueling station.

Fig. 12 depicts a vanadium halide redox flow system 120 that includes a vanadium halide redox cell 121 having a positive half cell 122, a negative half cell 125, and an ionically conductive separator 128, the positive half cell 122 containing a positive half cell solution 123 and a positive electrode 124, the negative half cell 125 containing a negative half cell solution 126 and a negative electrode 127, the ionically conductive separator 128 separating the positive half cell 122 from the negative half cell 125 and contacting the positive solution 123 on a side 128a adjacent the positive half cell 122 and the negative solution 126 on a side 128b adjacent the negative half cell 125. Positive solution reservoir 129 is coupled to positivehalf cell 122 through positive solution supply line 130 and return line 131. The return line 131 has a pump 132. Negative solution reservoir 133 includes a negative solution supply line 134 and a return line 135 coupled between negative solution reservoir 133 and negative half cell 125. Return line 135 has a pump 136. Power supply 137 is electrically coupled to positive electrode 124 at positive half-cell 122 through line 138 and to negative electrode 127 at negative half-cell 125 through line 139, switch 141, and line 140. An electrical extraction circuit 142 (which may be a resistor or the like) is electrically coupled to the positive electrode 124 at the positive half cell 122 through

lines

145 and 138 and to the negative electrode 127 at the negative half cell 125 through line 143, switch 144, line 146 and line 140. The

half cells

122 and 125 and

reservoirs

129 and 133 are tightly gas tight and the positive and

negative electrolyte solutions

123 and 126 may be degassed. The atmosphere above

solutions

123 and 126 in

half cells

122 and 125 and

reservoirs

129 and 133 can be an inert gas such as nitrogen, helium, argon, mixtures thereof, or the like.

In one particular method of operating the system 120, a positive half-cell solution 123 comprising a halide electrolyte, vanadium (III) halide, and vanadium (IV) halide is placed in the positive half-cell 122 and the positive solution reservoir 129, while a negative half-cell solution 126 having the same compounds as the positive half-cell 123, i.e., comprising a halide electrolyte, vanadium (III) halide, and vanadium (IV) halide, is placed in the negative half-cell 125 and the negative solution reservoir 133. The amounts of vanadium (III) halide, vanadium (IV) halide and halide ions in the positive and negative half-

cell solutions

123 and 126 are such that in the first charging step, the vanadium halide redox cell 121 can be specifically treated to have a state of charge selected from the group consisting of a zero state of chargeand a state of charge close to zero, the cell comprising predominantly vanadium (IV) halide in the halide electrolyte of the positive half-cell solution 123 and predominantly halide v (III) in the halide electrolyte of the negative half-cell solution 126. In the positive and

negative solutions

123 and 126, the halide is selected from the group consisting of bromide and a combination of bromide and chloride, and the bromide ion concentration is greater than the chloride ion concentration, and the total halide ion concentration is at least 3 times the total vanadium ion concentration. The positive half-cell solution 123 includes vanadium (III) halide and vanadium (IV) halide, the molar ratio of V (III) to V (IV) in the halogenated electrolyte is from about 0.9: 1 to about 6: 1, the negative half-cell solution 126 includes vanadium (III) halide and vanadium (IV) halide, the molar ratio of V (III) to V (IV) in the halogenated electrolyte is from about 0.9: 1 to about 6: 1, and the amount of negative half-cell solution 126 to the amount of positive half-cell solution 123 is equal to or about equal to the molar ratio of V (III) to V (IV). One particular advantage of forming the positive and negative half-

cell solutions

123 and 126 includes vanadium (III) halide and vanadium (IV) halide in a molar ratio of V (III) to V (IV) of about 1: 1, and wherein the amount of negative half-cell solution 126 to the amount of positive half-cell solution 123 is about 1: 1. Another particular advantage of forming the positive and negative half-

cell solutions

123 and 126 includes vanadium (III) halide and vanadium (IV) halide in a molar ratio of V (III) to V (IV) of about 2: 1, and wherein the amount of negative half-cell solution 126 to the amount of positive half-cell solution 123 is about 2: 1.

The first charging step can be performed by opening switch 144 and closing switch 141 and allowing sufficient current between

electrodes

124 and 127 while activating pumps 132 and 136so that positive half-cell solution 123 recirculates through positive half-cell 123 and negative half-cell solution 126 recirculates through negative half-cell 125 to form primarily vanadium (IV) halide in positive half-cell solution 123 and primarily vanadium (iii) halide in negative half-cell solution 126 without forming polyhalide complexes, wherein cell 121 is at or near zero state of charge. In a second charging step, charging is allowed to continue, so that the redox cell 121 is fully or partially charged, including the polyhalide complex and vanadium (V) ions in the positive half-cell solution 123 and vanadium (II) halide in the negative half-cell solution 126, wherein the molar amount of polyhalide complex and vanadium (V) to the molar amount of vanadium (II) halide is about stoichiometric balance (in the case where the redox cell 121 is fully or partially charged). Once the second charging step is complete (or partially complete), the redox cell 121 can be charged by opening switch 141, closing switch 144, turning on

pumps

132 and 136 so that positive half-cell solution 123 recirculates through positive half-cell 123 and negative half-cell solution 126 recirculates through negative half-cell 125 and electrical energy is drawn by electrical draw circuit 142. For example, once redox cell 121 is fully or partially charged to a zero state of charge or close to a zero state of charge, cell 121 may be recharged by repeating the second charging step described above. One advantage of the redox system of the present invention is that very little halogenated gas is generated above the positive half-cell solution 123 during the first and second charging processes.

In an alternative method of operating the system 120, the main vanadium (IV) halide in the halogenated electrolyte may be initially placed in the positive half-cell 122 and reservoir 129, while the main vanadium (iii) halide in the halogenated electrolyte may be placed in the negative half-cell 125 and reservoir 133, inamounts and capacities set so that the cell 121 is at or near zero state of charge. Next, the battery 121 may be charged according to the second charging step described above and discharged as described above.

Example 1

FIG. 6 shows that 60ml of 6M Br was contained in each half cell^-+2M Cl^-Initial charge-discharge curve of a vanadium halide redox flow battery containing 2MV (3.5+) solution. The cell adopts a Gore Select P-03430 membrane. The battery was initially charged to a voltage of 1.25V and discharged to a lower voltage limit of 0.25V at a constant current of 1.0 Amp. It appears that the ratio of initial charge time to discharge time is about 1.5, indicating that during initial charge, 1.5 electrons per mole of vanadium in the negative half cell are used to convert the V (3.5+) solution to V²⁺And in the positive half cell, at Br^-The ions being oxidized to Br₃ ^-Thereafter, the V (III) ions are oxidized to V (IV). The subsequent charge-discharge cycles give an average charge-to-discharge time ratio between 1.05 and 1.1, corresponding to a coulomb efficiency of 95% to 91%.

Example 2

A cell using a 3M vanadium (III)/(IV) bromide solution as the active material in both half-cells was set up and evaluated as follows:

50: 50 brominated vanadium (III)/vanadium (IV) (designated 3M V (3.5+)) was prepared by dissolving the desired amounts of vanadium trioxide and vanadium pentoxide powders in 8M hydrobromic acid. Hydrobromic acid was also added to make the final solution a chlorine concentration of 1.5M.

Figure 7 shows the cell voltage versus time during charge and discharge cycles for a cell containing 60.0ml of solution in each half cell and employing a Gore Select P-03430 membrane. The battery was charged to a voltage of 1.6V and discharged to the lower voltage limit of 0.25V at a constant current of 2.0 Amp. Assuming complete reaction of the vanadium ions in the negative half cell, the theoretical charge and discharge time was calculated to be 2.4 hours. This is above the applied voltage limit compared to the measured charge and discharge times of 2.1 and 2 hours, respectively, as shown in fig. 7. The coulomb efficiency is therefore considered to be over 95%. The cell was cycled for more than 30 cycles and the drop in capacity was found to be negligible, indicating that the v (iii)/v (iv) feed solution provides a stable electrolyte for the vanadium halide redox flow cell.

Example 3

3M V (3.5+) solution was prepared by mixing V in a 3: 1 molar ratio₂O₃∶V₂O₅The powders are provided in combination as follows:

using V₂O₃The mass of (A): 168.64g

Using V₂O₅The mass of (A): 62.21g

1000ml of 8M HBr are mixed with 150ml of 10M HCl, stirred and heated to approximately 80 ℃. Will V₂O₃The powder was added slowly to the HBr/HCl mixture, followed by the slow addition of V₂O₅And (3) powder. The solution was then heated to about 150 ℃ and held at that temperature for about 1 hour. The final amount was approximately 1010 ml. During the dissolution of the vanadium halide, negligible bromine was detected. However, when the same process was repeated by simultaneously adding vanadium trioxide and vanadium pentoxide powders to the HBr/HCl mixture, bromine gas was observed to form as the vanadium pentoxide oxidized bromide ions to bromine.

Example 4

A 4M vanadium bromide solution for use in a redox flow battery was prepared by the following method:

1.0.5 mol of V₂O₅And 1.5 moles of V₂O₃The powder is placed in two separate containersIn (1).

2.V₂O₅The powder was added to a beaker containing 0.8 liters of a 9-10M solution of HBr and V was added₂O₃The powder was added slowly and stirred continuously. The mixture was stirred for several hours until a blue solution of V (III)/IV bromide was obtained.

3. The solution was filtered and 10M HCl was added to bring the final chloride concentration to 2M before the volume reached 1 liter with the HBr solution.

Example 5

The 4M V (3.5+) solution was prepared by bringing the molar ratio V to 3: 1₂O₃∶V₂O₅The powder is provided by the following reaction:

using V₂O₃The mass of (A): 169.00g

Using V₂O₅The mass of (A): 68.50g

1000ml of 8M HBr are mixed with 150ml of 10M HCl, stirred and heated to about 80 ℃. V is added over a period of 25 minutes₂O₃Powder, followed by slow addition of V over a period of 15 minutes₂O₅Powder, so that the powder dissolves. The solution was then boiled for approximately 2 hours so that the final volume was 750 ml. No bromine was detected during dissolution and boiling.

Example 6

2M V (3.5+) solution was prepared by mixing V in a 3: 1 molar ratio₂O₃∶V₂O₅The powders were provided by mixing as follows:

using V₂O₃The mass of (A): 112.50g

Using V₂O₅The mass of (A): 45.55g

800ml of 8M HBr and 200ml of 10MHCl were stirred together at 60 ℃ with reflux (reluxing). V was added slowly over a period of more than 35 minutes₂O₃Powder, followed by addition of V₂O₅And (3) powder. It took about 20 minutes to add and dissolve the powders. Negligible bromine gas was detected. Heating and stirring were stopped 5 minutes after all the powder had dissolved. The cooled solution was then poured into a 1000ml flask and 63ml of distilled water was required to raise the solution to the 1000ml mark.

FIG. 8 shows a typical charge-discharge curve for a vanadium halide redox flow battery containing 100ml of 8M Br in each half-cell^-There was a solution of 2M V (3.5 +). The cell adopts a Gore Select L-01854 membrane. The battery was initially charged to a voltage of 1.6V and discharged to a lower voltage limit of 0.25V at a constant current of 1.0 Amp. Although not shown in the drawings, initiallyIs approximately 9 hours. This leads to the fact that: during initial charging, in the negative half-cell, 1.5 electrons per mole of vanadium are used to convert the V (3.5+) solution to V²⁺And in the positive half cell, the V (III) ion headIs first oxidized to V (IV) and then Br^-The ions being oxidized to Br₃ ^-. The second charge-discharge cycle gives charge and discharge times of 6 and 5.5 hours, respectively, corresponding to a coulombic efficiency of about 92%. The theoretical capacity of the cell using 110ml of 2M vanadium solution is approximately 5.9 hours, and therefore at 40mA/cm²The utilization rate of the active material at the current density of (3) is more than 93%.

Example 7

A volume of 250ml of a 2M V (3.33+) solution was obtained by chemically dissolving 4.5 to 1 molar ratio of vanadium trioxide and vanadium pentoxide powders in 8M HBr. This involves heating an 8M HBr solution to about 60 deg.C and slowly adding 30.75g of V under reflux₂O₃Powder until most dissolved. Then, by slowly adding 8.2g of V₂O₅Powders, mixed for about one hour and brought to complete dissolution by reflux. Finally, the solution was cooled, filtered and then added to both sides of the same vanadium halide redox flow battery as shown in example 6. However, in this example, 110ml of 2M V (3.3+) solution was added to the negative half cell, while only 55ml of the same solution was added on the positive side.

Fig. 9 shows a plot of voltage versus time for a battery obtained during cycles of charging and discharging the battery at a constant current of 1.0 Amp. Unlike the curve shown in fig. 3, more than one step is observed in the charging curve, which means that the ratio v (iii) in the initial feeding solution v (iv) is not exactly equal to 2: 1, thus creating a slight imbalance during the charging and discharging of the battery. This may lead to the fact that: the vanadium trioxide powder used for the preparation of this solution is partially oxidized to V during storage₂O₄Therefore, the content of v (iv) in the finally prepared solution is higher than desired. This imbalance in the vanadium ion ratio means that the positive side becomes overcharged during each charge, and more bromide ions and tribromide ions are formed than desired, thus resulting in the abnormal discharge behavior shown in fig. 4.

Assuming a 2: 1 ratio of V (III) to V (IV) and complete reaction of the vanadium ions in the negative half cell, the theoretical initial charge time for this cell was calculated to be 8.85 hours. It was compared to the measured initial charge time of 8.8 hours. The charge and discharge times for the subsequent cycles were measured to be 5.2 and 4.6 hours, respectively, above the applied voltage limit, as shown in fig. 9. The coulomb efficiency is therefore considered to be over 88%. In addition, the measured discharge time for this cell represents 84% of the discharge time obtained for the cell in fig. 3, with twice the amount of solution used in the positive half cell in fig. 3.

Example 8

The colloidal vanadium bromide electrolyte was tested in a static cell and its performance was compared to a non-colloidal solution. The following procedure was used to prepare colloidal vanadium bromide solutions:

approximately 50g of a solution containing 2M vanadium (3.5+), 6.4M HBr and 2M HCl was added to a 250ml beaker, and 2.5g (5% wt) of fumed silica (aerosil 300) was added to the beaker. These compounds were stirred for one minute using a hand-held mixer and left for 10 minutes. The gel was transferred to a sealed glass bottle.

To construct a static cell, copper electrodes were adhered to the plastic cell casing. The copper electrode and glassy carbon will then be placed together to form a conductive surface. A rubber frame was stuck on top of the glassy carbon sheet and a piece of carbon felt was cut to fit within the rubber frame. All of these parts are adhered using silicone. This felt is covered with a film, which is also adhered to the rubber frame with silicone. This configuration is repeated and adhered to the opposite face of the film.

Prior to cell construction, the carbon felt was immersed in a V (3.5+) solution with fumed silica in a vacuum oven at room temperature for 25 minutes. The impregnation is carried out before the solution gels. If gelation has occurred, a simple shaking of the solution of gum is carried out to bring it back to the liquid state, thus enabling impregnation of the mat. The amount of solution/glue not absorbed by the mat is measured before the mat is inserted into the rubber frame as described above. The entire battery is bolted together and connected to a power source and recorder.

Figure 10 shows the charge-discharge curve of a static cell employing colloidal vanadium bromide electrolyte.

Example 9

The effect of polyethylene glycol (PEG) as a complexing agent for bromine generated in the positive half cell during charging was evaluated. The cell was assembled using an L-Gore 01854 film and fmi (usa) graphite felt electrode against a glassy carbon substrate and a copper current collector. The charge and discharge cycles of this cell were performed using the following electrolytes:

1) 2M vanadium (3.5+) in 8M HBr

2) Comprises 50ml of PEG and 50ml of a solution containing 2M vanadium (3.5+) in 8M HBr

3) Contains 25ml of PEG and 75ml of a solution containing 2M vanadium (3.5+) in 8M HBr

Before starting the cell, 40ml of the solution to be tested was injected into each of the two reservoirs. The pump was started and the solution was circulated for one hour.

From fig. 11A, 11B and 11C, the average coulombic efficiency for all solutions was approximately 90%. From these results, the following conclusions can be drawn: the addition of PEG to the 2M vanadium bromide solution did not have a significant effect on coulombic efficiency. However, the two batteries with solutions containing PEG had lower average voltage efficiencies than the solutions without any PEG. It is believed that the decrease in voltage efficiency is due to an increase in resistance of the PEG-containing solution, which is caused by an increase in viscosity of the PEG-containing electrolyte solution.

Although the voltage efficiency drops in the presence of 25% and 50% PEG, it is important to note that during cycling, the PEG-containing cells did not exhibit bromine vapor, while the PEG-free cells exhibited significant amounts of bromine vapor in the electrolyte reservoir and tubes. Thus, PEG is very effective in coagulating bromine to prevent or reduce the formation of vapors in the cell. By reducing the concentration of PEG, a reduction is possible.

Claims

1. A vanadium halide redox cell prior to charging comprising:

so that in a first charging step comprising charging the vanadium halide redox cell prior to charging, a vanadium halide redox cell is prepared having a state of charge selected from the group consisting of a zero state of charge and a state of charge close to zero, the cell comprising predominantly vanadium (IV) halide in the positive half-cell solution and predominantly vanadium (iii) halide in the negative half-cell solution.

2. The pre-charge vanadium halide redox cell of claim 1 wherein the amounts of vanadium (III) halide, vanadium (IV) halide, and halide ions in the positive half cell solution and the negative half cell solution are such that:

so that in a second charging step comprising charging the vanadium halide redox cell in a zero state of charge, a charged vanadium halide redox cell is prepared, which comprises a polyhalide complex in a positive half-cell solution and vanadium (II) halide in a negative half-cell solution.

3. The pre-charge vanadium halide redox cell of claim 1 wherein the positive half-cell solution comprises vanadium (III) halide and vanadium (IV) halide in a halide electrolyte, wherein the molar ratio of v (III) to v (IV) is from about 0.9: 1 to about 6: 1; and is

The negative half-cell solution comprises vanadium (III) halide and vanadium (IV) halide, wherein the molar ratio of V (III) to V (IV) is from 0.9: 1 to about 6: 1; and is

Wherein the amount of negative half-cell solution to the amount of positive half-cell solution is equal to or about equal to the molar ratio of V (III) to V (IV).

4. The pre-charge vanadium halide redox cell of claim 3 wherein the positive half cell solution and the negative half cell solution comprise vanadium (III) halide and vanadium (IV) halide in a molar ratio of V (III) to V (IV) of about 1: 1 and wherein the amount of negative half cell solution to the amount of positive half cell solution is about 1: 1.

5. The pre-charge vanadium halide redox cell of claim 3 wherein the positive half cell solution and the negative half cell solution comprise vanadium (III) halide and vanadium (IV) halide in a molar ratio of V (III) to V (IV) of about 2: 1 and wherein the amount of negative half cell solution to the amount of positive half cell solution is about 2: 1.

6. The pre-charge vanadium halide redox cell of claims 1-5 wherein the total halide ion concentration is at least 3 times the total vanadium ion concentration.

7. The pre-charge vanadium halide redox cell of claim 1, 2 or 3 wherein the halide is selected from the group consisting of bromide and a combination of bromide and chloride.

8. The pre-charge vanadium halide redox cell of claim 1, 2, 3, 4 or 5 wherein the halide is selected from the group consisting of bromide and a combination of bromide and chloride wherein the bromide ion concentration is greater than the chloride ion concentration and the total halide ion concentration is at least 3 times the total vanadium ion concentration.

9. A vanadium halide redox cell in a state selected from the group consisting of a zero state of charge and a state of charge close to zero, the vanadium halide redox cell comprising:

a positive half-cell having a positive half-cell solution comprising a halogenated electrolyte and a vanadium halide, the vanadium halide comprising primarily Vanadium (VI) halide;

wherein the amount of vanadium (IV) halide in the positive half-cell solution and the amount of vanadium (III) halide in the negative half-cell solution are set such that the vanadium halide redox cell is in a state of charge selected from the group consisting of a zero state of charge and a state of charge close to zero.

10. The vanadium halide redox cell of claim 9 wherein the total halogen ion concentration is at least 3 times the total vanadium ion concentration.

11. Thevanadium halide redox cell of claim 9 wherein the positive half cell solution does not include a substantial amount of the polyhalide complex at or near zero charge.

12. The vanadium halide redox cell of claim 9, 10 or 11 wherein the halide is selected from the group consisting of bromide and a combination of bromide and chloride.

13. The vanadium halide redox cell of claim 9, 10, or 11 wherein the halide is selected from the group consisting of bromide and a combination of bromide and chloride wherein the concentration of bromide ions is greater than the concentration of chloride ions and wherein the concentration of total halide ions is at least 3 times the concentration of total vanadium ions.

14. A fully charged vanadium halide redox cell comprising:

15. The vanadium halide redox cell of claim 13 wherein the number of moles of polyhalide complex to moles of vanadium (II) halide is about 1: 2.

16. The vanadium halide redox cell of claim 13 wherein the moles of polyhalide complex to moles of vanadium (II) halide are in the range of about 0.7: 2 to about 1.3: 2.

17. The vanadium halide redox cell of claim 14, 15 or 16 wherein the halide is selected from the group consisting of bromide and a combination of bromide and chloride.

18. The vanadium halide redox cell of claim 14, 15 or 16 wherein the halide is selected from the group consisting of bromide and a combination of bromide and chloride wherein the concentration of bromide ions is greater than the concentration of chloride ions and wherein the total concentration of halide ions is at least 3 times the total concentration of vanadium ions.

19. A partially charged vanadium halide redox cell comprising:

wherein the moles of polyhalide complex and vanadium (V) to the moles of vanadium (II) halide are approximately stoichiometrically balanced.

20. The vanadium halide redox cell of claim 19 wherein the number of moles of polyhalide complex to moles of vanadium (II) halide is about 1: 2.

21. The vanadium halide redox cell of claim 19 wherein the moles of polyhalide complex to moles of vanadium (II) halide are in the range of about 0.7: 2 to about 1.3: 2.

22. The vanadium halide redox cell of claims 19, 20 and 21 wherein the halide is selected from the group consisting of bromide and a combination of bromide and chloride.

23. The vanadium halide redox cell of claim 19, 20, or 21 wherein the halide is selected from the group consisting of bromide and a combination of bromide and chloride wherein the concentration of bromide ions is greater than the concentration of chloride ions and wherein the total concentration of halide ions is at least 3 times the total concentration of vanadium ions.

24. The vanadium halide redox cell of claims 1, 9, 14 or 19 wherein the halide further comprises bromide and the halide electrolyte further comprises a complexing agent for bromine.

25. The vanadium halide redox cell of claims 1, 9, 14 or 19 wherein the halide electrolyte is fixed or gelled.

26. The vanadium halide redox cell of claims 1, 9, 14 or 19 wherein the halide electrolyte is fixed or gelled and wherein the fixing or gelling agent is fumed silica.

27. A method of producing an electrolyte for a vanadium halide redox cell, comprising:

the V (III) compound and the V (V) compound are dissolved in a solution of HBr, LiBr, NaBr, KBr, or mixtures thereof in a molar ratio of about 3: 1 to produce a mixture of V (III) and V (IV) ions in solution of about 50: 50.

28. The method of claim 27, wherein the V (III) compound is V₂O₃And V (V) the compound is V₂O₅。

29. A method ofproducing an electrolyte for a vanadium halide redox cell, comprising:

equal moles of V (III) and V (IV) compounds are dissolved in a solution of HBr, LiBr, NaBr, KBr, or a mixture thereof to produce an approximately 50: 50 mixture of V (III) and V (IV) ions in solution.

30. The method of claim 29, wherein the V (III) compound is V₂O₃And the V (IV) compound is V₂O₄。

31. The method of any one of claims 27 to 30, wherein the solution further comprises chloride ions.

32. A method of producing an electrolyte for a vanadium halide redox cell, comprising:

the V (III) compound and the V (V) compound were dissolved in a 4.5: 1 molar ratio in a solution of HBr, LiBr, NaBr, KBr or a mixture thereof to produce a 2: 1 mixture of V (III) and V (IV) ions.

33. The method of claim 32, wherein the V (III) compound is V₂O₃And V (V) the compound is V₂O₅。

34. A method of producing an electrolyte for a vanadium halide redox cell, comprising:

a2: 1 molar ratio of V (III) compound and V (IV) compound is dissolved in a solution of HBr, LiBr, NaBr, KBr, or a mixture thereof to produce a 2: 1 mixture of V (III) and V (IV) ions.

35. The method of claim 34, wherein the V (III) compound is V₂O₃And the V (IV) compound is V₂O₄。

36. The method of any one of claims 27, 29, 32 or 34, wherein the total vanadium ion concentration is between 0.5 and 5M and the total bromide ion concentration is between 2 and 12M.

37. The method of any one of claims 27, 29, 32 or 34, wherein the electrolyte is HBr and the total bromide concentration is 2 to 12M.

38. A method according to any one of claims 27, 29, 32 or 34, wherein the electrolyte further comprises chloride ions at a concentration of 0.5 to 3M.