High-stability flow battery electrolyte and preparation method thereof

Abstract

The invention provides a high-stability flow battery electrolyte and a preparation method thereof, organic molecules are added into a positive electrode solution of the high-stability flow battery electrolyte, and the organic molecules are organic molecules with the decomposition potential of 1.0 V or above. The positive electrode solution is a vanadium-containing electrolyte, and the vanadium concentration is 1.5-2.5 mol / L. And the positive electrode solution is an H2SO4 system electrolyte and / or an HCl system electrolyte. The organic molecule is one or a mixture of more of chloroethanol, chloroacetaldehyde, chloroacetic acid, acrylic acid, n-pentanoic acid and CCl4. Aiming at the defects that the existing electrolyte is easy to precipitate at a high temperature under a high SOC and oxidizes an electrode due to overcharge, the invention provides an organic matter molecule with proper oxygen reduction potential, so that the organic matter molecule reacts under the high SOC and plays a protection role, and the problem that the electrolyte is unstable due to the high SOC in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to liquid flow battery electrolyte technology, and in particular to a high-stability liquid flow battery electrolyte and a preparation method thereof. Background Art

[0002] All-vanadium, Fe-Cr, Na-S, Zn-Br and other metal ion flow batteries are currently developing strong momentum of green environmental protection energy storage batteries, all of which are redox energy storage flow batteries with different valence ions as positive and negative active materials dissolved in supporting electrolytes in a liquid circulating flow state. Among them, all-vanadium and other flow batteries have been expanded and applied in renewable energy storage, power grid peak regulation, backup power supply and other fields, and the installed capacity is increasing by GW every year.

[0003] The electrolyte is the storage carrier of electrical energy in the all-vanadium liquid flow battery system and an important component of the vanadium battery. It determines the energy density of the battery system and directly affects the stability of the battery system.

[0004] However, since the flow battery is charged and discharged based on the redox of positive and negative ion pairs, its disadvantage is that under high SOC (charging rate) and high temperature, the redox pairs are easily precipitated from the solution, blocking the carbon felt electrode and making it lose conductivity. The precipitates block the flow channel and storage tank, causing the battery system to collapse.

[0005] In addition, when the battery is charged to a high SOC, due to the reduction of reaction substrates, short-term overcharging will cause oxidation damage to the electrode plates, causing the plates to lose conductivity and causing the single-cell voltage to increase until it burns out.

[0006] In this way, in order to avoid the above defects, the existing processing methods have to implement restrictive operating conditions, add sensitive control systems to reduce charging SOC, add external thermal management equipment, etc. These measures significantly increase the complexity of battery operation and the cost of the entire system.

[0007] Therefore, there is an urgent need to improve existing redox flow battery systems.

[0008] For all-vanadium batteries, in 2013, the Pacific Northwest Laboratory in the United States published a study that provided a solution based on Cl- and SO4 2- Combined with the redox flow battery solution as the supporting electrolyte, the introduction of Cl- can significantly improve the stability of vanadium ions in the solution, and can increase the upper limit of the operating temperature of the traditional flow redox battery from ≦38℃ to ≦45℃ (forming a stable neutral species VO2Cl(H2O)2). At the same time, when the solution is in a high SOC state, high concentration VO 2+ It reacts with Cl- to generate Cl2, which can avoid the strong oxidizing VO under overcharge to a certain extent. 2+ Oxidation of the electrode.

[0009] Alternatively, a method of strictly limiting the battery SOC can be adopted, that is, the system charge and discharge SOC range is maintained in the range of 30-70%, which can also prevent battery electrode oxidation to a limited extent. However, at this time, the electrolyte utilization rate is low, which has a greater impact on the overall operating cost of the system.

[0010] 1) The existing pure H2SO4 system has poor temperature resistance, and low temperature and low SOC operation leads to low total energy density of the system (<20Wh / L);

[0011] 2) The difficulty of operating HCl electrolyte and the increase in operating costs;

[0012] Although the use of HCl-containing electrolyte technology has improved the system's high-temperature resistance and energy density (~32Wh / L), the introduction of high-concentration Cl- also brings risks: the precipitation of a large amount of Cl2 causes serious corrosion of battery-related materials, requiring the use of high-cost corrosion-resistant materials, while increasing the environmental risks of the system and placing higher demands on operators. Therefore, the reasonable control of chlorine gas production during battery operation is an issue that needs to be urgently addressed. Summary of the invention

[0013] The purpose of the present invention is to solve the problem that under high SOC and high temperature of the existing electrolyte system, the redox couple is easy to precipitate out from the solution, blocking the carbon felt electrode to make it lose conductivity, and the precipitate blocks the flow channel and storage tank, causing the battery system to collapse. A high-stability liquid flow battery electrolyte is proposed. The liquid flow battery electrolyte is a high-temperature stable all-vanadium (V) electrolyte that has a protective effect on the electrode. n+ ) electrolyte. Under high SOC and high temperature, the organic molecules in the electrolyte can decompose to produce secondary metabolites until they are completely oxidized to CO2, which plays a role in protecting the high temperature stability of the electrolyte and the electrode.

[0014] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising", etc. and similar meanings, as well as closed-ended "composed of", "composed of", etc. and similar meanings.

[0015] To achieve the above object, the technical solution adopted by the present invention is: a high-stability liquid flow battery electrolyte, wherein organic molecules are added to the positive electrode solution, and the organic molecules are organic molecules with a decomposition potential of more than 1.0V.

[0016] Furthermore, the decomposition potential of the organic molecule is preferably 1-1.25V.

[0017] Furthermore, the decomposition potential of the organic molecule is more preferably 1.05-1.15V.

[0018] Furthermore, the cathode solution is an H2SO4 system electrolyte and / or an HCl system electrolyte.

[0019] Furthermore, the concentration of H2SO4 in the cathode solution is 1.0-3.0 mol / L.

[0020] Furthermore, the HCl concentration in the cathode solution is 2.0-5.0 mol / L.

[0021] Furthermore, the cathode solution is a vanadium-containing electrolyte, and the vanadium concentration is 1.5-2.5 mol / L.

[0022] Furthermore, in the positive electrode solution of the H2SO4 system electrolyte, the vanadium concentration is 1.5-1.9 mol / L.

[0023] Furthermore, the vanadium concentration in the positive electrode solution of the HCl system electrolyte is 1.6-2.4 mol / L.

[0024] Furthermore, the organic molecule is a mixture of one or more of chloroethanol, chloroacetaldehyde, chloroacetic acid, acrylic acid, n-valeric acid and CCl4.

[0025] Furthermore, when the organic molecule is a mixture of one or more of chloroethanol, chloroacetaldehyde and chloroacetic acid, the decomposition potential of the mixture is 1.1±0.05V, and the decomposition potential of chloroethanol is 1.13V.

[0026] Furthermore, when the organic molecule is a mixture of one or more of chloroethanol, chloroacetaldehyde and chloroacetic acid, the concentration of the organic molecule added to the cathode solution is 0.1-0.3 mol / L, preferably 0.15-0.25 mol / L.

[0027] Furthermore, when the organic molecule is a mixture comprising one or more of acrylic acid, n-valeric acid and CCl4, the decomposition potential of the mixture is 1.2±0.05V.

[0028] Furthermore, when the organic molecule is a mixture of one or more of acrylic acid, n-valeric acid and CCl4, the concentration of the organic molecule added to the cathode solution is 0.1-0.2 mol / L, preferably 0.12-0.16 mol / L.

[0029] Furthermore, when the organic molecule is a mixture of multiple species including acrylic acid, n-valeric acid and CCl4, adding two or more substances together can slow down the oxidation rate of one of the substances, avoiding excessive current density causing a violent reaction of the additives to generate a large number of bubbles and a rapid decrease in concentration.

[0030] Another object of the present invention is to disclose a method for preparing a high-stability liquid flow battery electrolyte, comprising the following steps: adding organic molecules to a H2SO4 and / or HCl electrolyte containing vanadium, stirring until completely dissolved, and adding HCl or H2SO4 and water to make the volume to the desired concentration.

[0031] Furthermore, the stirring temperature is 25-55° C., and the stirring time is 0.5-4 h.

[0032] The invention discloses a high-stability liquid flow battery electrolyte and a preparation method thereof. The liquid flow battery electrolyte of the invention is a high-temperature stable all-vanadium (V n+ ) electrolyte. Specifically, the present invention has the following advantages compared with the prior art:

[0033] 1) When the flow battery is charged, as the positive electrode V 5+ The concentration gradually increases, and the positive electrode reaction potential gradually increases. 5+ When the concentration reaches a certain value (SOC>85%), the absolute potential of the positive electrode of the vanadium battery will be>1.25V. At this time, if the positive electrode solution is at a high temperature>40℃, the risk of precipitation and crystallization is very high; when the electrolyte SOC>80%, the VO2 in the positive electrode solution available for reaction is 2+ Insufficient, at this time when the input current is not reduced or the solution flow rate is insufficient (concentration polarization is not reduced), the carbon felt and plate as conductors will replace VO 2+ Oxidation reaction occurs and it burns and loses its conductive function.

[0034] Under high SOC, organic molecules of a specific concentration in the electrolyte of the high-stability liquid flow battery of the present invention begin to participate in the reaction to buffer the damage caused by insufficient substrate to the solution and electrodes. When the SOC of the positive electrode vanadium electrolyte is greater than 85% (positive electrode potential greater than 1.2V), the organic molecules in the electrolyte of the high-stability liquid flow battery of the present invention begin to decompose and produce secondary metabolites until they are completely oxidized to CO2, which plays a role in maintaining the high temperature stability of the electrolyte and protecting the electrodes.

[0035] 2) The decomposition potential of the organic molecules added to the electrolyte of the high-stability liquid flow battery of the present invention is preferably 1-1.25V, more preferably 1.05-1.15V. If the decomposition potential of the organic molecules is too high, for example, when an organic molecule with a decomposition potential of 1.6V is selected, the reaction potential of vanadium at the positive electrode is only 1.0-1.4V. After the vanadium oxidation reaction is completed, the reaction potential of the organic matter has not yet been reached. At this time, the excess current begins to oxidize the carbon felt. In this case, the organic matter cannot play a compensatory reaction to protect the carbon felt electrode and stabilize the electrolyte; for example, when the decomposition potential of the organic molecules is too low, for example, when an organic molecule with a decomposition potential of <0.8V is selected, the positive electrode vanadium ion (1.0-1.4V) has not started to react, and the organic matter with a lower redox potential is more likely to undergo oxidation reaction and complete the reaction first, which does not play a protective role when the vanadium ion reaches the end point of the reaction.

[0036] 3) It has been tested that under the same charge and discharge conditions, within the same time period (within 200 charge and discharge cycles), the high-stability liquid flow battery electrolyte of the present invention to which organic molecules (such as chlorohydrin, aldehydes or acrylic substances) are added is compared with the blank control example, and the increase in the surface resistance of the carbon felt electrode and the bipolar plate is 30-50% lower than that of the control group.

[0037] 4) According to experimental tests, under the same SOC and temperature conditions, the electrolyte with organic molecules added in the present invention is compared with the blank control electrolyte, and the precipitation time at a high temperature of 45°C is prolonged by >30%.

[0038] 5) The high-stability liquid flow battery electrolyte added with organic molecules of the present invention can effectively control the resistivity of the plate after multiple charge and discharge cycles under the action of small organic molecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a comparison diagram of energy decay of the high stability liquid flow battery electrolyte of Example 1 and the battery of Control Group 1;

[0040] Figure 2 Surface corrosion diagrams of bipolar plates of high-stability flow battery electrolyte of Example 4 (left side in the figure) and control group 4 (right side in the figure) after long-term charge and discharge operation. DETAILED DESCRIPTION

[0041] The present invention is further described below with reference to the examples. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0042] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0043] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0044] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0045] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0046] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0047] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 15-25°C.

[0048] In this manual, the reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0049] Example 1

[0050] This embodiment discloses a high-stability liquid flow battery electrolyte, which contains SO4 2- =4.3mol / L, V n+ =1.72mol / L and chloroacetaldehyde = 0.15mol / L. (where n represents the sum of V ions of different valence states, i.e., the total vanadium of the positive and negative electrodes is 1.72mol / L)

[0051] The preparation method is as follows: add chloroacetaldehyde organic molecules to H2SO4 electrolyte containing 3.5-valent V ions, stir for 2 hours at 30°C until completely dissolved, and add H2SO4 and water to make up to the set concentration.

[0052] Comparative Example 1

[0053] This comparative example discloses a vanadium redox flow battery electrolyte, which is substantially the same as Example 1, except that it does not contain chloroacetaldehyde.

[0054] The various properties of Example 1 and Comparative Example 1 are tested below.

[0055] Table 1 Effect of charge and discharge on the resistivity of electrode plates

[0056]

[0057] From the data of Example 1, it can be seen that under the same operating conditions and electrolyte temperature, after 100 charge and discharge cycles, the resistivity of the battery electrode plate and the carbon felt electrode loaded with the high-stability liquid flow battery electrolyte of this example is maintained at a low level. The experimental results show that the addition of chloroacetaldehyde organic molecules can enable the electrolyte to obtain effective protection for the electrodes under high SOC conditions.

[0058] Example 2

[0059] This embodiment discloses a high-stability liquid flow battery electrolyte, which contains V n+ =2.22mol / L, SO4 2- =2.3mol / L, Cl-=4.6mol / L, chloroethanol=0.15mol / L. (where n represents the sum of ions of different valence states, i.e., the total vanadium of the positive and negative electrodes is 2.22mol / L)

[0060] The preparation method is as follows: in a solution containing 3.5 valent V n+ Add chloroethanol organic molecules to the H2SO4 and HCl electrolyte, stir at 30℃ for 1h until completely dissolved, and add HCl, H2SO4 and water to make up to the set concentration.

[0061] Comparative Example 2

[0062] This comparative example discloses a vanadium redox flow battery electrolyte which is substantially the same as Example 2 except that it does not contain chloroethanol.

[0063] The various properties of Example 2 and Comparative Example 2 are tested below.

[0064] Table 2 Effect of charge and discharge on the resistivity of electrode plates

[0065]

[0066] It can be seen from the data of Example 2 that under the same operating conditions and electrolyte temperature, after 100 charge and discharge cycles, the resistivity of the battery electrode plates and carbon felt electrodes loaded with the high-stability liquid flow battery electrolyte of this example is maintained at a low level. The experimental results show that the addition of chloroethanol organic molecules can enable the electrolyte to obtain effective protection for the electrodes under high SOC conditions.

[0067] Example 3

[0068] This embodiment discloses a high-stability liquid flow battery electrolyte, which contains H2SO4=2.0 mol / L, HCl=5.5 mol / L, V n+=1.65mol / L, acrylic acid 0.15mol / L, n-valeric acid 0.1mol / L. (where n represents the sum of ions of different valence states, i.e., the total vanadium of the positive and negative electrodes is 1.65mol / L)

[0069] The preparation method is as follows: in a solution containing 3.5 valent V n+ Acrylic acid and n-valeric acid were added to the H2SO4 and HCl electrolytes respectively, stirred at 40°C for 0.5h until completely dissolved, and HCl, H2SO4 and water were added to make up to the set concentration.

[0070] Comparative Example 3-1

[0071] This comparative example discloses a vanadium redox flow battery electrolyte, which is substantially the same as Example 3, except that it does not contain acrylic acid and n-valeric acid.

[0072] The various properties of Example 3 and Comparative Example 3-1 are tested below.

[0073] Table 3 Effect of charge and discharge on the resistivity of electrode plates

[0074]

[0075] As shown in Table 3, under the same charge and discharge conditions and in the same time period, the surface resistance increase of the bipolar plate in this embodiment is about 50% lower than that of the electrolyte in Comparative Example 3-1 by introducing acrylic acid and n-valeric acid organic molecules into the positive electrode solution. It can be seen that under the protection of acrylic acid and n-valeric acid organic molecules, the resistivity of the plate is effectively controlled after multiple charge and discharge cycles, and the high temperature stability of the positive electrode solution is improved.

[0076] Comparative Example 3-2

[0077] This comparative example discloses a vanadium redox flow battery electrolyte which is substantially the same as Example 3 except that it contains only n-valeric acid.

[0078] The various properties of Example 3 and Comparative Example 3-2 are tested below.

[0079] Table 3 Effect of charge and discharge on the resistivity of electrode plates

[0080]

[0081] As shown in Table 3, under the same charge and discharge conditions and in the same time period, in Control Example 3-2, only n-valeric acid organic molecules were introduced into the positive electrode solution. After 200 charge and discharge operations, the resistivity increase of the bipolar plate was lower than that of the electrolyte in Control Example 3-1, but higher than that in Example 3. Similarly, the high temperature 45°C stabilization time was 25% longer than that in Control Example 3-1, but lower than that in Example 3. It can be seen that the mixed addition of acrylic acid and n-valeric acid is better than the addition of n-valeric acid alone.

[0082] Example 4

[0083] This embodiment discloses a high-stability liquid flow battery electrolyte, which contains 0.1 mol / L acrylic acid, 0.05 mol / L carbon tetrachloride (CCl4), V n+ =1.75mol / L, SO4 2- =4.3mol / L. (where n represents the sum of ions of different valence states, i.e. the total vanadium in both the positive and negative electrodes is 1.75mol / L)

[0084] Acrylic acid and CCl4 were added to the above 3.5-valent H2SO4 electrolyte respectively, stirred at 30°C for 3 h until completely dissolved, and HCl and water were added to make up to the set concentration.

[0085] Comparative Example 4

[0086] This comparative example discloses a flow battery electrolyte which is substantially the same as Example 4 except that it does not contain acrylic acid and carbon tetrachloride.

[0087] The various properties of Example 4 and Comparative Example 4 are tested below.

[0088] Table 4 Comparison of static high temperature stability of positive electrode high SOC solution

[0089]

[0090] *The above stability time refers to the time when the solution has visible precipitation.

[0091] Table 5 Comparison of static low temperature stability of negative electrode trivalent solutions

[0092]

[0093] As shown in Table 4, under the same cathode solution, the same SOC and temperature conditions, the precipitation time of Example 4 was extended by 60% compared with that of Control Example 4. It can be seen that after adding acrylic acid and CCl4, the compensatory oxidation of acrylic acid and CCl4 in the solution at high SOC slowed down the VO2 + The ions precipitate V2O5 at high temperatures. At the same time, at low temperatures of -15°C, the presence of additives has no effect on the low-temperature stability of the solution.

[0094] The various performance testing methods of Examples 1-4 and Comparative Examples 1-4 are as follows:

[0095] 1) Charge and discharge operation mode:

[0096] All charging and discharging modes of the present invention are: constant current charging-current density 110mA / cm 2To 1.6V voltage; Constant voltage charging: Constant voltage 1.6V charging until the battery OCV is up to 1.54V; Constant current discharge: Current density 110mA / cm 2 The constant current discharge is to a voltage of 1 V. The system power used is 2 kW, and the electrolyte volume is 60 L for both the positive and negative electrodes.

[0097] 2) The average operating temperature of the battery system is ≤45°C.

[0098] 3) Temperature resistance experiment: High and low temperature stability test of positive and negative electrode solutions. After the battery is fully charged, the positive electrode solution (5-valent) is placed in a 55°C water bath to observe the precipitation. After the battery is fully discharged, the negative electrode solution (3-valent) is placed in a -15°C constant temperature box to observe the crystallization.

[0099] like Figure 1 As shown, when the battery system was at 45 degrees Celsius and underwent 80 high SOC charge and discharge cycles, the experimental group containing stabilizers acrylic acid and carbon tetrachloride maintained 84% of the discharge capacity, but the control group without stabilizer only maintained 32%. This shows that the stabilizer has a good stabilizing effect on the electrolyte, and the electrolyte did not show precipitation or other phenomena that affect battery performance.

[0100] like Figure 2 The following are the surface morphology pictures of the bipolar plates after disassembly of two batteries in Example 4. After the battery was at 45 degrees Celsius and experienced 80 high SOC charge and discharge cycles, the battery plates containing the combination of acrylic acid and CCl4 stabilizer were only slightly oxidized, while the control group had severe surface deformation. The resistivity of the former was 0.15mΩ·cm, while the latter increased to 1.3mΩ·cm.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-stability liquid flow battery electrolyte, characterized in that: The positive electrode solution is added with organic molecules, wherein the organic molecules have a decomposition potential of 1.0V or more.

2. The high-stability liquid flow battery electrolyte according to claim 1, characterized in that: The cathode solution is a vanadium-containing electrolyte, and the vanadium concentration is 1.5-2.5 mol / L.

3. The high stability liquid flow battery electrolyte according to claim 1, characterized in that: The cathode solution is an H2SO4 system electrolyte and / or an HCl system electrolyte.

4. The high-stability liquid flow battery electrolyte according to claim 3, characterized in that: The concentration of H2SO4 in the cathode solution is 1.0-3.0 mol / L; And / or, the HCl concentration in the cathode solution is 2.0-5.0 mol / L.

5. The high-stability liquid flow battery electrolyte according to claim 1, characterized in that: The organic molecules are a mixture of one or more of chloroethanol, chloroacetaldehyde, chloroacetic acid, acrylic acid, n-valeric acid and CCl4.

6. The high-stability liquid flow battery electrolyte according to claim 5, characterized in that: The organic molecules are a mixture comprising acrylic acid, n-valeric acid and CCl4.

7. The high-stability liquid flow battery electrolyte according to claim 6, characterized in that: When the organic molecule is a mixture of one or more of chloroethanol, chloroacetaldehyde and chloroacetic acid, the concentration of the organic molecule added to the cathode solution is 0.1-0.3 mol / L.

8. The high-stability liquid flow battery electrolyte according to claim 6, characterized in that: When the organic molecule is a mixture of one or more of acrylic acid, n-valeric acid and CCl4, the concentration of the organic molecule added to the cathode solution is 0.1-0.2 mol / L.

9. A method for preparing a high-stability liquid flow battery electrolyte according to any one of claims 1 to 8, characterized in that: The following steps are involved: Add organic molecules to the H2SO4 and / or HCl electrolyte containing V, stir until completely dissolved, and add HCl or H2SO4 and water to make up to the required concentration.

10. The method for preparing a high-stability liquid flow battery electrolyte according to claim 9, characterized in that: The stirring temperature is 25-55°C, and the stirring time is 0.5-4h.

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