A low-temperature resistant liquid flow battery electrolyte and its application

Abstract

The present invention discloses a low-temperature resistant electrolyte for a liquid flow battery and its application, belonging to the technical field of electrochemical energy storage. By adding a certain amount of additives to the electrolyte of a zinc-bromine liquid flow battery, the additives being choline chloride or a mixture of choline chloride and N-methyl-N-ethylmorpholinium bromide, the assembled zinc-bromine liquid flow battery can stably operate for a long time at a current density of 40 mA cm-2 under the condition of -10 °C, and maintain normal charge and discharge of the battery under the condition of -20 °C. It can prevent the solidification of the charging products at the positive electrode of the zinc-bromine liquid flow battery, broaden the temperature window of the battery, expand its scope of use, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and particularly relates to a low-temperature resistant zinc-bromine flow battery electrolyte and its application. Background Art

[0002] With the gradual depletion of non-renewable resources represented by fossil energy and the environmental pollution problems brought about during their use, the utilization and development of renewable resources have become a global consensus. However, due to problems such as the intermittency and instability of renewable resources, it is necessary to improve their effective utilization rate. Energy storage technology, as the "bank" of energy, stores the energy generated by renewable resources and converts it into stable electric energy for transmission, thereby solving the problem of difficult grid connection of renewable resources. Large-scale energy storage technologies are generally divided into two categories: physical energy storage and electrochemical energy storage. Physical energy storage such as compressed air energy storage and pumped-storage energy storage has high requirements for the geographical environment, and its application range is greatly limited. Among electrochemical energy storage, flow batteries have the advantages of good safety, long life, low cost, independent design of capacity and power, and being unaffected by the environmental location, making them an ideal large-scale energy storage technology.

[0003] There are various types of flow batteries. Among them, zinc-bromine flow batteries have received extensive attention due to their high theoretical energy density (430 Wh / kg), stable operation, long life, and abundant raw materials with low cost. During charging, a large amount of Br2 is generated in zinc-bromine flow batteries, and additives need to be used to fix it in the electrolyte to reduce bromine volatilization and corrosion. However, the introduction of additives causes the complexation products to solidify at low temperatures, resulting in a sharp increase in internal polarization of the battery and causing battery failure. This has restricted the wide application of zinc-bromine flow batteries. Research and development of new low-temperature resistant zinc-bromine flow battery electrolyte additives have become an important topic that needs to be studied urgently. Summary of the Invention

[0004] To solve the above technical problems, the present invention aims to provide a new low-temperature resistant electrolyte and its application in zinc-bromine flow batteries.

[0005] The specific technical solution adopted by the present invention is as follows:

[0006] An aqueous electrolyte, wherein the electrolyte contains bromide ions and an additive, and the additive is choline chloride (ChCl) or a mixture of choline chloride (ChCl) and N-methyl-N-ethyl morpholinium bromide (MEM).

[0007] Further, the total concentration of the additive is 0.1 - 1.5 mol / L -1 , preferably 0.5 - 1.5 mol / L -1 .

[0008] Further, the molar ratio of N-methyl-N-ethylmorpholinium bromide (MEM) to choline chloride (ChCl) in the additive is 0-2:1, preferably 0-1:1, more preferably 0-1:2.

[0009] Further, the source of bromide ions in the electrolyte is ZnBr2, and the concentration of ZnBr2 is 0.1-3 mol / L -1 , preferably 1-2 mol / L -1 .

[0010] Further, the electrolyte also contains KCl, and the concentration of KCl is 0.1-3.5 mol / L -1 , preferably 2-3 mol / L -1 .

[0011] On the other hand, the present invention provides the application of the above aqueous electrolyte and / or additive in a zinc-bromine flow battery.

[0012] Further, the aqueous electrolyte and / or additive is applied to the electrolyte of the zinc-bromine flow battery to fix Br2 generated during charging and reduce the volatilization and corrosion of Br2, and the application temperature is -20 to 30 °C.

[0013] Further, the zinc-bromine flow battery is a single-flow battery, the electrolyte on the negative electrode side circulates, and the electrolyte on the positive electrode side does not flow.

[0014] Further, the zinc-bromine flow battery mainly consists of a carbon positive electrode, a membrane and a carbon negative electrode.

[0015] Further, the carbon positive electrode is selected from one or more of carbon felt, activated carbon, graphite, graphene, carbon nanotubes and framework carbon, preferably carbon felt.

[0016] Further, the membrane is selected from one of Daramic porous membrane and Nafion membrane, preferably Daramic porous membrane.

[0017] Further, the carbon negative electrode is selected from one or more of carbon felt, activated carbon, graphite, graphene, carbon nanotubes and framework carbon, preferably carbon felt.

[0018] The beneficial effects of the present invention compared with the prior art are as follows:

[0019] 1. The electrolyte of the present invention can prevent the bromine complex product during charging of the zinc-bromine flow battery from solidifying at low temperature, and the zinc-bromine flow battery can stably operate for a long time at a current density of 40 mA / cm² -2 under the condition of -10 °C, and the battery can also maintain normal charge and discharge when the temperature is -20 °C, broadening the temperature window of the zinc-bromine flow battery and expanding its application range.

[0020] 2. The additive of the present invention is ChCl or a mixture of ChCl and MEM. The higher the content of ChCl, the better the low-temperature performance of the battery. The increase in the content of MEM can improve the coulombic efficiency of the battery at room temperature. By adding an appropriate amount of additive to the electrolyte of the zinc-bromine flow battery and adjusting the concentration of the additive and the ratio of the mixed additive under different low-temperature environments, the long-life and high-performance operation of the battery at normal and low temperatures can be achieved. Brief Description of the Drawings

[0021] To more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments will be briefly introduced below.

[0022] Figure 1 Battery performance of the zinc-bromine flow batteries of Examples 1-6 at different temperatures (0°C, -5°C, -10°C, -15°C, and -20°C), where a to f represent Examples 1 to 6 respectively;

[0023] Figure 2 Battery performance of the zinc-bromine flow batteries of Comparative Examples 1-6 at different temperatures (0°C, -5°C, -10°C, -15°C, and -20°C), where a to f represent Comparative Examples 1 to 6 respectively;

[0024] Figure 3 Battery cycle performance of Examples 1-6 at -10°C; a to f represent Examples 1 to 6 respectively;

[0025] Figure 4 Voltage-time change curves of Comparative Examples 1-6 at -10°C; a to f represent Comparative Examples 1 to 6 respectively;

[0026] Figure 5 Battery cycle performance of Examples 1-6 at room temperature; a to f represent Examples 1 to 6 respectively;

[0027] Figure 6 Battery cycle performance of Comparative Examples 1-6 at room temperature; a to f represent Comparative Examples 1 to 6 respectively;

[0028] Figure 7 Battery cycle performance diagram of Example 5 at -20°C. Detailed Embodiments

[0029] The present invention will be described in detail below with reference to the embodiments. However, the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, without creative efforts, obtaining other similar embodiments will fall within the protection scope of the present invention.

[0030] Example 1:

[0031] Prepare a mixed electrolyte of 2 mol / L ZnBr2, 3 mol / L KCl, and 0.6 mol / L choline chloride (ChCl), and assemble a zinc-bromine flow battery for testing.

[0032] To characterize the low-temperature resistance performance of the above-prepared electrolyte, a zinc-bromine flow battery was assembled as the test object. The battery is a single-flow battery, with the electrolyte on the negative electrode side circulating and the electrolyte on the positive electrode side not flowing. The positive and negative electrode materials are both carbon felt, the separator is a Daramic porous membrane, and the test current density is 40 mA cm -2 。

[0033] Example 2:

[0034] Prepare a mixed electrolyte of 2 mol / L ZnBr2, 3 mol / L KCl, and 0.8 mol / L choline chloride (ChCl), and assemble a zinc-bromine flow battery for testing.

[0035] The test of the low-temperature resistance performance of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Example 2 is used for testing.

[0036] Example 3:

[0037] Prepare a mixed electrolyte of 2 mol / L ZnBr2, 3 mol / L KCl, and 1.0 mol / L choline chloride (ChCl), and assemble a zinc-bromine flow battery for testing.

[0038] The test of the low-temperature resistance performance of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Example 3 is used for testing.

[0039] Example 4:

[0040] Prepare a mixed electrolyte of 2 mol / L ZnBr2, 3 mol / L KCl, and 1.2 mol / L choline chloride (ChCl), and assemble a zinc-bromine flow battery for testing.

[0041] The test of the low-temperature resistance performance of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Example 4 is used for testing.

[0042] Example 5:

[0043] Prepare a mixed electrolyte of 2 mol / L ZnBr2, 3 mol / L KCl, 0.2 mol / L 1-ethyl-2-methylmorpholinium bromide (MEM), and 0.8 mol / L ChCl (the molar ratio of MEM:ChCl is 1:4), and assemble a zinc-bromine flow battery for testing.

[0044] The low-temperature resistance performance test of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Example 5 is used for the test.

[0045] Example 6:

[0046] Prepare a mixed electrolyte of 2 mol / L ZnBr2, 3 mol / L KCl, 0.4 mol / L MEM and 0.6 mol / L ChCl (the molar ratio of MEM:ChCl is 2:3), and assemble a zinc-bromine flow battery for testing.

[0047] The low-temperature resistance performance test of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Example 6 is used for the test.

[0048] Comparative Example 1:

[0049] Prepare a mixed electrolyte of 2 mol / L ZnBr2, 3 mol / L KCl and 1.0 mol / L 1-ethyl-2-methylpyrrolidinium bromide (MEP), and assemble a zinc-bromine flow battery for testing.

[0050] The low-temperature resistance performance test of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Comparative Example 1 is used for the test.

[0051] Comparative Example 2:

[0052] Prepare a mixed electrolyte of 2 mol / L ZnBr2, 3 mol / L KCl and 1.0 mol / L 1-ethyl-2-methylmorpholinium bromide (MEM), and assemble a zinc-bromine flow battery for testing.

[0053] The low-temperature resistance performance test of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Comparative Example 2 is used for the test.

[0054] Comparative Example 3:

[0055] Prepare a mixed electrolyte of 2 mol / L ZnBr2, 3 mol / L KCl, 0.2 mol / L 1-ethyl-2-methylpyrrolidinium bromide (MEP) and 0.8 mol / L ChCl (the molar ratio of MEP:ChCl is 1:4), and assemble a zinc-bromine flow battery for testing.

[0056] The low-temperature resistance performance test of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Comparative Example 3 is used for the test.

[0057] Comparative Example 4:

[0058] Prepare a mixed electrolyte containing 2 mol / L ZnBr2, 3 mol / L KCl, 0.2 mol / L 1-ethyl-2-methylpyridinium bromide (BCA15), and 0.8 mol / L ChCl (the molar ratio of BCA15:ChCl is 1:4), and assemble a zinc-bromine flow battery for testing.

[0059] The low-temperature resistance performance test of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Comparative Example 4 is used for testing.

[0060] Comparative Example 5:

[0061] Prepare a mixed electrolyte containing 2 mol / L ZnBr2, 3 mol / L KCl, 0.6 mol / L MEM, and 0.4 mol / L ChCl (the molar ratio of MEM:ChCl is 3:2), and assemble a zinc-bromine flow battery for testing.

[0062] The low-temperature resistance performance test of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Comparative Example 5 is used for testing.

[0063] Comparative Example 6:

[0064] Prepare a mixed electrolyte containing 2 mol / L ZnBr2, 3 mol / L KCl, 0.8 mol / L MEM, and 0.2 mol / L ChCl (the molar ratio of MEM:ChCl is 4:1), and assemble a zinc-bromine flow battery for testing.

[0065] The low-temperature resistance performance test of the prepared electrolyte is the same as that of the electrolyte in Example 1, except that the electrolyte prepared in Comparative Example 6 is used for testing.

[0066] Table 1: Coulombic efficiency of Examples 1-6 and Comparative Examples 1-6

[0067]

[0068] Note: M represents mol / L; BCA15 represents 1-ethyl-2-methylpyridinium bromide.

[0069] Figure 1 For the variable-temperature cycle efficiency of zinc-bromine single-flow batteries using the electrolytes of Examples 1 to 6 at 0 to (-20)°C, it can be seen that Examples 2 to 5 have stable Coulombic efficiency, voltage efficiency, and energy efficiency, and the efficiency of Example 6 decreases slightly. Although Example 1 cannot maintain normal efficiency at -20°C, it remains stable and has a relatively high efficiency above -15°C. Relatively speaking,Figure 2 Comparative Examples 1-6 showed extremely poor performance at low temperatures. Even though Comparative Example 3 had slightly more stable performance at -15°C, it could not ensure long-term cycling of the battery at low temperatures and had a short lifespan (see Figure 4 ). Figure 3 Among them, except for Example 4, the battery could cycle nearly 200 times under the condition of constant temperature at -10°C. The reason for the slightly worse cycling performance of Example 4 was that the high concentration of the additive decreased the conductivity of the electrolyte. Among Comparative Examples 1-6, except for Comparative Example 3, the other comparative examples could only complete a few cycles at -10°C, further indicating that the condition for the zinc-bromine single-flow battery to operate at low temperatures was to use ChCl with a suitable concentration alone as an additive, or to select MEM and ChCl with an appropriate mixing ratio as an additive. Comparative Examples 1-2 showed that the commonly used MEP or MEM alone could not meet the low-temperature operation of the battery, and Comparative Examples 3-4 showed that when used in combination, only the mixture of MEM and ChCl was unique, and the other mixing strategies could not solve the problem of solidification of the positive electrode product of the zinc-bromine flow battery during charging. Moreover, MEM and ChCl were not simply mixed, but had a definite mixing ratio. When the proportion of MEM was too high, its coulombic efficiency at room temperature was high while its low-temperature performance was poor; when the proportion of ChCl was too high, its low-temperature lifespan was long while the coulombic efficiency of the battery at room temperature was low (see Figure 5 , 6 and Table 1). Therefore, an appropriate mixing ratio should be selected according to actual needs. Figure 7 It was further demonstrated that this mixed additive could also maintain the normal operation of the battery at a lower temperature (-20°C).

[0070] Generally speaking, in order to ensure the normal operation of the zinc-bromine single-flow battery at low temperatures, it was necessary to use ChCl or a mixture of ChCl and MEM as an additive to maintain the low-temperature performance of the battery. However, when ChCl was used alone, its coulombic efficiency at room temperature was slightly insufficient. Therefore, it was necessary to select a suitable additive and the mixing ratio of the additive according to the actual usage situation. For example, in the northwest of China, cold and low-temperature weather accounted for a large proportion of the year, so it was preferred to use ChCl alone as an additive; in the southeast of China, the temperature changed greatly, being cold in winter and hot in summer, so choosing an appropriate mixing ratio of MEM and ChCl as the additive of the battery could meet its high-efficiency and long-life operation. At a temperature of 0 to (-20)°C, the total concentration of the additive was in the range of 0.6 - 1.2 mol / L. As the temperature decreased, the higher the total concentration of the additive and the higher the proportion of choline chloride, the more excellent the comprehensive performance; when the temperature was -20°C, using pure choline chloride with a concentration of 1.0 - 1.2 mol / L had the best comprehensive performance.

[0071] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and 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. Application of an aqueous electrolyte in a zinc-bromine flow battery, characterized in that, The described aqueous electrolyte is applied to the electrolyte of a zinc-bromine flow battery, and the application temperature of the electrolyte is -20~0°C; The electrolyte contains bromide ions and additives, and the additives are a mixture of choline chloride (ChCl) and N-methyl-N-ethylmorpholinium bromide (MEM); The molar ratio of N-methyl-N-ethylmorpholinium bromide (MEM) to choline chloride (ChCl) is 1:4 or 2:

3.

2. The application according to claim 1, wherein The total concentration of the additive is 0.4 - 1.4 mol / L -1 .

3. The application according to claim 2, characterized in that The total concentration of the additive is 0.6 - 1.2 mol / L -1 .

4. The application according to claim 1, characterized in that The source of bromide ions in the electrolyte described above is ZnBr2, and the concentration of ZnBr2 is 0.1 - 3 mol / L -1 .

5. The application according to claim 4, characterized in that, The concentration of ZnBr2 is 1 - 2 mol / L -1 .

6. The application according to claim 1, characterized in that, The electrolyte also contains KCl, and the concentration of KCl is 0.1 - 3.5 mol / L -1 .

7. The application according to claim 6, wherein The concentration of KCl is 2 - 3 mol / L -1 .

8. The application according to claim 1, characterized in that, The described zinc-bromine flow battery is a single-flow battery, and the electrolyte on the negative electrode side circulates, while the electrolyte on the positive electrode side does not flow.

9. The application according to claim 1, characterized in that, The zinc-bromine flow battery mainly consists of a carbon positive electrode, a membrane, and a carbon negative electrode.

10. The application according to claim 9, characterized in that, The carbon positive electrode is selected from one or more of carbon felt, activated carbon, graphite, graphene, carbon nanotubes, and framework carbon; the membrane is selected from one of Daramic porous membrane and Nafion membrane; the carbon negative electrode is selected from one or more of carbon felt, activated carbon, graphite, graphene, carbon nanotubes, and framework carbon.

11. The application according to claim 10, wherein The carbon positive electrode is selected from carbon felt; the membrane is selected from Daramic porous membrane; the carbon negative electrode is selected from carbon felt.

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