Ionic liquid-based active material, preparation method thereof, and lithium-bromine flow battery

Abstract

The present invention proposes an ionic liquid-based active material and a preparation method thereof and a lithium-bromine flow battery, which belongs to the technical field of lithium-bromine flow batteries and is used to solve the technical problems of active particle agglomeration and limited electron transport in existing lithium slurry flow batteries. The present invention mixes pyrrole ionic liquid and lithium bromide and reacts them to prepare a lithium-bromine flow battery and its ionic liquid-based active material. The present invention proposes a lithium-based flow battery, which combines the advantages of high energy density and high average output voltage of lithium batteries, and avoids the disadvantages caused by solid particles in lithium slurry batteries. The ionic liquid-based active material provided by the present invention is liquid at room temperature or higher temperature and can be used directly as an electrolyte without the addition of other organic solvents. Compared with other types of lithium battery electrolytes, it is more environmentally friendly and safer. The use of cheap microporous membranes greatly reduces the cost of batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-bromine flow batteries, and in particular relates to an ionic liquid-based active material and a preparation method thereof, and a lithium-bromine flow battery. Background Art

[0002] With the continuous growth of global energy demand and the rapid development of renewable energy, long-duration energy storage technology has become crucial for addressing the instability and intermittency of energy supply. Since the concept of flow batteries was proposed in 1974, scholars in Australia, Japan, Canada, the United Kingdom, the United States, and other countries have proposed various systems: aqueous flow, all-organic flow, lithium slurry flow, and organic targeted flow batteries. Lithium batteries, with their high energy density and high average output voltage, are currently the predominant technology for energy storage applications. Their active materials are stored within each cell. Unlike lithium-ion batteries, the active materials in flow batteries are stored in external tanks. Pumps and pipelines transport the active materials to the stack for redox reactions, achieving power and energy decoupling. Lithium slurry batteries combine the advantages of lithium batteries and flow batteries, offering high output voltage and energy density, with the active materials stored in external tanks. They are considered a promising large-scale energy storage technology. However, the active material of lithium slurry batteries is not dissolved in the electrolyte, but dispersed in the organic electrolyte in the form of particles. The active particles have movements such as convection, dispersion and re-agglomeration. The connectivity between particles is constantly changing, and electron transport is limited and complex. Therefore, there are problems such as easy sedimentation, high viscosity, poor conductivity and complex fluid behavior, which limit its commercial application.

[0003] Patent publication number CN 105514531 A discloses a lithium-ion-halogen flow battery. The electrolyte of the battery is composed of a lithium halide as an active material, a lithium salt as a supporting electrolyte, a halogen complexing agent, and a non-aqueous solvent. The lithium halide is one or more of lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; the halogen complexing agent is one or more of a quaternary ammonium bromide, nitrogen methyl ethyl pyrrolidine bromide, and nitrogen methyl ethyl pyridine bromide; the supporting electrolyte lithium salt is one or more of LiBF4, LiClO4, LiFP6, LiAsF6, LiN(SO2CF3)2, and LiSO2CF3; and the non-aqueous solvent includes ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate among esters; and one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, tetraglyme, DMSO, and an ionic liquid among ethers. In this patent, a halogen element complexing agent is used to form a complex with a halogen element. Summary of the Invention

[0004] The present invention provides an ionic liquid-based active material, a preparation method thereof, and a lithium-bromine flow battery, which overcome the problems of active particle agglomeration and limited electron transport in existing lithium slurry flow batteries.

[0005] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] An ionic liquid-based active substance with the following structural formula:

[0007] , where R is -CH2CH(CH3)2, -C n H 2n+1 One of (n≥4), x=0.1~1.

[0008] A method for preparing an ionic liquid-based active substance comprises the following steps: mixing a pyrrole ionic liquid and lithium bromide and reacting the mixture to obtain the ionic liquid-based active substance.

[0009] The structural formula of the pyrrole ionic liquid is as follows:

[0010]

[0011] Wherein, R is -CH2CH(CH3)2, -C n H 2n+1 One of (n≥4).

[0012] Preferably, the pyrrole ionic liquid is one or more of N-methyl-N-butylpyrrole bromide, N-methyl-N-isobutylpyrrole bromide, N-methyl-N-pentylpyrrole bromide, N-methyl-N-hexylpyrrole bromide, and N-methyl-N-heptylpyrrole bromide.

[0013] The molar ratio of the pyrrole ionic liquid to lithium bromide is 1:(0.1~1).

[0014] The molar ratio of the pyrrole ionic liquid to lithium bromide is 1:(0.5-1).

[0015] The reaction temperature is 40-70° C. and the reaction time is 24-72 hours.

[0016] A lithium-bromine flow battery comprises a battery module, a positive electrode electrolyte storage tank, a negative electrode electrolyte storage tank, a circulation pump and a circulation pipeline; the battery module comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte; the electrolyte is an ionic liquid-based active substance.

[0017] The positive electrode and the negative electrode are both selected from carbon felt or carbon cloth; the separator is a microporous membrane; and all connecting parts need to be sealed.

[0018] The positive and negative electrode reactions in the lithium-bromine flow battery are as follows:

[0019] positive electrode:

[0020]

[0021] negative electrode:

[0022] .

[0023] The operating temperature of the lithium-bromine flow battery is 25-60° C. The obtained ionic liquid-based active material is liquid in the range of 25-60° C. and serves as both the active material and the electrolyte of the lithium-bromine flow battery without the addition of other solvents.

[0024] Beneficial effects of the present invention: The present invention proposes a lithium-bromine flow battery that not only takes advantage of the high energy density and high average output voltage of lithium batteries, but also avoids the disadvantages of solid particles in lithium slurry batteries. The selected pyrrole ionic liquid has a relatively negative cathode limiting potential, which can be used in the negative electrode Li + The resulting lithium-bromine flow battery ionic liquid-based active material remains stable within the redox potential range of 0.1% to 0.1% Li, and reversibly complexes Br2 molecules generated at the positive electrode. The resulting lithium-bromine flow battery ionic liquid-based active material is liquid at room temperature or higher, and can be used directly as an electrolyte without the addition of other organic solvents. Compared to other types of lithium battery electrolytes, it is more environmentally friendly and safer. The use of inexpensive microporous membranes significantly reduces battery costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 It is a structural schematic diagram of the present invention.

[0027] Figure 2 Schematic diagram of the battery module. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0029] Example 1

[0030] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0031] Lithium bromide (0.5 mol) and N-methyl-N-butylpyrrole bromide (1 mol) were mixed and heated to 60°C under nitrogen until a clear, transparent, and uniform target liquid appeared. The product was washed three times with dichloromethane (100 mL × 3) and vacuum dried at 60°C for 24 h to obtain the desired lithium-bromine flow battery ionic liquid-based active material [BMPyr]Li 0.5 Br 1.5 The water content was measured with a Karl Fischer titrator and was 8 ppm.

[0032] The structure of lithium-bromine flow battery is as follows Figure 1 As shown, it includes a battery module, a positive electrode electrolyte storage tank, a negative electrode electrolyte storage tank, a circulation pump and a circulation pipeline; the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank are connected to the battery module through the circulation pipeline; the circulation pump is set on the circulation pipeline to circulate the positive and negative electrolytes, and the connection parts between all components are sealed to prevent the electrolyte from contacting the outside air. The battery module includes a positive electrode, a negative electrode, a diaphragm and an electrolyte. Specifically, as Figure 2 As shown, the battery module includes end plates at both ends of the positive and negative electrodes, and a sealing gasket frame, a current collector, a sealing ring, a bipolar plate, an electrode frame, an electrode and a diaphragm are sequentially arranged between the end plates, and an electrolyte outflow port and an electrolyte inflow port are provided on the end plates. In this embodiment, a sealing gasket frame and a sealing ring made of nitrile rubber material are placed between the end plate and the current collector, and at the electrolyte inlet and outlet of the battery module. The electrode frame is also made of nitrile rubber material to ensure the sealing of the battery. A microporous membrane is used as a diaphragm to separate the positive and negative electrode chambers of the battery, and carbon felt is used as the positive and negative electrodes. The electrode area is 4cm 2 [BMPyr]Li is directly used as the positive and negative electrolytes. 0.5 Br 1.5 The battery module charge and discharge current is 20mA / cm 2 The electrolyte flow rate is 5 mL / min. The battery has a coulombic efficiency of 90%, an energy efficiency of 55%, and a voltage efficiency of 61%.

[0033] Example 2

[0034] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0035] Lithium bromide (1 mol) and N-methyl-N-isobutylpyrrole bromide (1 mol) were mixed and heated to 60°C under nitrogen until a clear, transparent, and homogeneous target liquid appeared. The product was then washed three times with dichloromethane (100 mL x 3) and vacuum-dried at 60°C for 24 hours to obtain the desired lithium-bromine flow battery ionic liquid-based active material [BisoMPyr]LiBr2. The water content was measured using a Karl Fischer titrator and was 9 ppm.

[0036] The positive and negative electrode compartments of the battery are separated by a microporous membrane, and carbon felt is used as the positive and negative electrodes, with an electrode area of ​​4 cm 2 [BisoMPyr]LiBr2 was used as the positive and negative electrolytes. Nitrile rubber was placed at all battery connections to ensure the battery's tightness. The battery was placed in a temperature-controlled box at a test temperature of 50°C and a charge and discharge current of 20 mA / cm 2 The electrolyte flow rate is 5 mL / min. The battery has a coulombic efficiency of 95%, an energy efficiency of 65%, and a voltage efficiency of 68%.

[0037] Example 3

[0038] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0039] Lithium bromide (0.7 mol) and N-methyl-N-heptylpyrrole bromide (1 mol) were mixed and heated to 50°C under nitrogen until a clear, transparent, and uniform target liquid appeared. The product was washed three times with dichloromethane (100 mL × 3) and vacuum dried at 60°C for 24 h to obtain the desired lithium-bromine flow battery ionic liquid-based active material [C7MPyr]Li 0.7 Br 1.7 The water content was measured with a Karl Fischer titrator and was 8 ppm.

[0040] The positive and negative electrode compartments of the battery are separated by a microporous membrane, and carbon felt is used as the positive and negative electrodes, with an electrode area of ​​4 cm 2 [C7MPyr]Li is directly used as the positive and negative electrolytes. 0.7 Br 1.7 All battery connections are covered with nitrile rubber to ensure the battery's tightness. The battery is placed in a temperature-controlled box, the test temperature is 60°C, and the charge and discharge current is 20mA / cm 2 The electrolyte flow rate is 5 mL / min. The battery has a coulombic efficiency of 98%, an energy efficiency of 70%, and a voltage efficiency of 71%.

[0041] Example 4

[0042] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0043] Lithium bromide (1 mol) and N-methyl-N-heptylpyrrole bromide (1 mol) were mixed and heated to 50°C under nitrogen until a clear, transparent, and homogeneous target liquid appeared. The product was then washed three times with dichloromethane (100 mL x 3) and vacuum-dried at 60°C for 24 hours to obtain the desired lithium-bromine flow battery ionic liquid-based active material [C7MPyr]LiBr2. The water content was measured using a Karl Fischer titrator and was 7 ppm.

[0044] The positive and negative electrode compartments of the battery are separated by a microporous membrane, and carbon felt is used as the positive and negative electrodes, with an electrode area of ​​4 cm 2 [C7MPyr]LiBr2 was used as the positive and negative electrolytes. Nitrile rubber was placed at all battery connections to ensure the battery's tightness. The battery was placed in a temperature-controlled box at a test temperature of 70°C and a charge and discharge current of 20 mA / cm 2 The electrolyte flow rate is 5 mL / min. The battery has a coulombic efficiency of 92%, an energy efficiency of 47%, and a voltage efficiency of 51%.

[0045] Comparative Example 1

[0046] Lithium bromide (1 mol) and N-methyl-N-ethylpyrrole bromide (1 mol) were mixed and heated to 110°C under nitrogen until a clear, transparent, and homogeneous liquid was formed. The product was then washed three times with dichloromethane (100 mL x 3) and vacuum-dried at 60°C for 24 hours to obtain the desired lithium-bromine flow battery ionic liquid active material [EMPyr]LiBr2. The water content was measured using a Karl Fischer titrator and was 6 ppm.

[0047] The positive and negative electrode compartments of the battery are separated by a microporous membrane, and carbon felt is used as the positive and negative electrodes, with an electrode area of ​​4 cm 2 [EMPyr]LiBr2 was used as the positive and negative electrolytes. Nitrile rubber was placed at all battery connections to ensure the battery's tightness. The battery was placed in a temperature-controlled box at a test temperature of 70°C and a charge and discharge current of 20 mA / cm 2 The electrolyte flow rate is 5 mL / min. The coulombic efficiency of the battery is 50%, the energy efficiency is 10%, and the voltage efficiency is 20%.

[0048] Comparative Example 2

[0049] Lithium bromide (1 mol) and 1-butyl-3-methylimidazolium bromide (1 mol) were mixed and heated to 70°C under nitrogen until a clear, transparent, and homogeneous target liquid appeared. The product was washed three times with dichloromethane (100 mL x 3) and vacuum-dried at 60°C for 24 hours to obtain the desired lithium-bromine flow battery ionic liquid-based active material [BMIm]LiBr2. The water content was measured using a Karl Fischer titrator and was 9 ppm.

[0050] The positive and negative electrode compartments of the battery are separated by a microporous membrane, and carbon felt is used as the positive and negative electrodes, with an electrode area of ​​4 cm 2 [BMIm]LiBr2 was used as the positive and negative electrolytes. Nitrile rubber was placed at all battery connections to ensure the battery's tightness. The battery was placed in a temperature-controlled box at a test temperature of 60°C and a charge and discharge current of 20 mA / cm 2 The electrolyte flow rate is 5 mL / min. The battery has a coulombic efficiency of 30%, an energy efficiency of 7%, and a voltage efficiency of 23%.

[0051] In Examples 1 to 4, the coulombic efficiency is greater than 90%, while in Comparative Example 1, since the cathode limiting potential of N-methyl-N-ethylpyrrole bromide is about -2V, it is impossible to Li + / Li redox potential range, so during the cycle, the electrolyte structure is irreversibly destroyed and the battery efficiency is low. Similarly, the cathode limiting potential of 1-butyl-3-methylimidazolium bromide in Comparative Example 2 is also about -2V, and the electrochemical window of most imidazolium ionic liquids is between Li + / Li redox potential range cannot remain stable, so this technical solution discovered a more stable pyrrole ionic liquid.

[0052] Example 5

[0053] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0054] Lithium bromide (0.5 mol) and N-methyl-N-butylpyrrole bromide (1 mol) were mixed and heated to 70°C under nitrogen until a clear, transparent, and uniform target liquid appeared. The product was washed three times with dichloromethane (100 mL × 3) and vacuum dried at 60°C for 24 h to obtain the desired lithium-bromine flow battery ionic liquid-based active material [BMPyr]Li 0.5 Br 1.5 .

[0055] Example 6

[0056] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0057] Lithium bromide (0.1 mol) and N-methyl-N-butylpyrrole bromide (1 mol) were mixed and heated to 60°C under nitrogen until a clear, transparent, and uniform target liquid appeared. The product was washed three times with dichloromethane (100 mL × 3) and vacuum dried at 60°C for 24 h to obtain the desired lithium-bromine flow battery ionic liquid-based active material [BMPyr]Li 0.1 Br 1.1 .

[0058] Example 7

[0059] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0060] Lithium bromide (1 mol) and N-methyl-N-butylpyrrole bromide (1 mol) were mixed and heated to 60°C under nitrogen until a clear, transparent, and uniform target liquid appeared. The product was washed three times with dichloromethane (100 mL × 3) and vacuum-dried at 60°C for 24 h to obtain the desired lithium-bromine flow battery ionic liquid-based active material [BMPyr]LiBr2.

[0061] Example 8

[0062] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0063] Lithium bromide (0.5 mol) and N-methyl-N-isobutylpyrrole bromide (1 mol) were mixed and heated to 60°C under nitrogen until a clear, transparent, and uniform target liquid appeared. The product was washed three times with dichloromethane (100 mL × 3) and vacuum dried at 60°C for 24 h to obtain the desired lithium-bromine flow battery ionic liquid-based active material [BisoMPyr]Li 0.5 Br 1.5 .

[0064] Example 9

[0065] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0066] Lithium bromide (1 mol) and N-methyl-N-isobutylpyrrole bromide (1 mol) were mixed and heated to 40°C under nitrogen until a clear, transparent, and uniform target liquid appeared. The product was washed three times with dichloromethane (100 mL × 3) and vacuum dried at 60°C for 24 h to obtain the desired lithium-bromine flow battery ionic liquid-based active material [BisoMPyr]LiBr2.

[0067] Example 10

[0068] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0069] Lithium bromide (0.1 mol) and N-methyl-N-heptylpyrrole bromide (1 mol) were mixed and heated to 50°C under nitrogen until a clear, transparent, and uniform target liquid appeared. The product was washed three times with dichloromethane (100 mL × 3) and vacuum dried at 60°C for 24 h to obtain the desired lithium-bromine flow battery ionic liquid-based active material [C7MPyr]Li 0.1 Br 1.1 .

[0070] Example 11

[0071] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0072] Lithium bromide (1 mol) and N-methyl-N-heptylpyrrole bromide (1 mol) were mixed and heated to 50°C under nitrogen until a clear, transparent, and uniform target liquid appeared. The product was washed three times with dichloromethane (100 mL × 3) and vacuum dried at 60°C for 24 h to obtain the desired lithium-bromine flow battery ionic liquid-based active material [C7MPyr]LiBr2.

[0073] Example 12

[0074] A method for preparing an ionic liquid-based active substance comprises the following steps:

[0075] Lithium bromide (0.5 mol) and N-methyl-N-heptylpyrrole bromide (1 mol) were mixed and heated to 50°C under nitrogen until a clear, transparent, and uniform target liquid appeared. The product was washed three times with dichloromethane (100 mL × 3) and vacuum dried at 60°C for 24 h to obtain the desired lithium-bromine flow battery ionic liquid-based active material [C7MPyr]Li 0.5 Br 1.5 .

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An ionic liquid-based active material, characterized in that The structural formula is as follows: , where R is -CH2CH(CH3)2 or -C n H 2n+1 , n=4~7, x=0.1~1.

2. The method for preparing the ionic liquid-based active material according to claim 1, characterized in that: The method comprises the following steps: mixing a pyrrole ionic liquid and lithium bromide and reacting them to obtain an ionic liquid-based active substance; the structural formula of the pyrrole ionic liquid is as follows: Wherein, R is -CH2CH(CH3)2 or -C n H 2n+1 , n=4~7.

3. The method for preparing an ionic liquid-based active substance according to claim 2, wherein: The molar ratio of the pyrrole ionic liquid to lithium bromide is 1:(0.1~1).

4. The method for preparing an ionic liquid-based active substance according to claim 3, wherein: The molar ratio of the pyrrole ionic liquid to lithium bromide is 1:(0.5-1).

5. The method for preparing an ionic liquid-based active substance according to claim 4, characterized in that: The reaction temperature is 40-70° C. and the reaction time is 24-72 hours.

6. A lithium-bromine flow battery, characterized in that It comprises a battery module, a positive electrode electrolyte storage tank, a negative electrode electrolyte storage tank, a circulation pump and a circulation pipeline that are sealed and connected to each other; the battery module comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte; it is characterized in that the electrolyte is the ionic liquid-based active material according to claim 1.

7. The lithium-bromine flow battery according to claim 6, characterized in that: The positive electrode and the negative electrode are both selected from carbon felt or carbon cloth; and the separator is a microporous membrane.

8. The lithium-bromine flow battery according to claim 7, characterized in that: The positive and negative electrode reactions in the lithium-bromine flow battery are as follows: positive electrode: negative electrode: 。 9. The lithium-bromine flow battery according to claim 8, characterized in that: The operating temperature of the lithium-bromine flow battery is 25-60°C.

Images