Application of carnitine hydrochloride in zinc-bromine flow battery electrolyte, zinc-bromine flow battery electrolyte and battery

Abstract

The invention belongs to the technical field of zinc-bromine flow batteries, and particularly relates to application of carnitine hydrochloride in a zinc-bromine flow battery electrolyte, the zinc-bromine flow battery electrolyte and a battery. According to the invention, the carnitine hydrochloride with high hydrophilicity is used as the bromine complexing agent to be applied to the zinc-bromine flow battery electrolyte to form a homogeneous electrolyte, so that the problem that the traditional bromine complexing agent is easy to generate phase separation is solved; the carnitine hydrochloride is applied to the electrolyte of the zinc-bromine flow battery, so that cross diffusion of bromine can be inhibited, and the cycling stability of the battery is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of zinc-bromine flow battery technology, specifically relating to the application of carnitine hydrochloride in zinc-bromine flow battery electrolyte, zinc-bromine flow battery electrolyte and battery. Background Technology

[0002] With increasingly severe energy and environmental challenges, the transformation to a green and low-carbon energy structure has become particularly important. While renewable energy sources such as wind and solar power possess enormous development potential, they still face a series of problems, including instability, randomness, and indirectness. Therefore, promoting innovation and research and development of efficient energy storage technologies has become a key pathway to achieving sustainable development goals. Among numerous energy storage technologies, flow batteries stand out due to their unique power-capacity decoupling architecture, excellent long cycle life, and environmentally friendly characteristics, becoming the preferred technology for constructing medium- to large-scale energy storage systems. Within the flow battery family, zinc-bromine flow batteries (ZBFB) have successfully attracted widespread attention from the energy storage industry due to their high theoretical energy density of up to 430 Wh / kg, low-cost active materials, and excellent cycle stability.

[0003] Despite significant progress in the practical application of zinc-bromine flow batteries, many challenges remain. Among these are the challenges related to the Br2 / Br2 ratio on the positive electrode side. - The slow redox kinetics limit the battery's operating current and power density. Furthermore, bromine cross-diffusion causes severe self-discharge, reducing coulombic efficiency and accelerating capacity decay. To address these challenges, researchers have delved into key components of zinc-bromine flow batteries, such as membranes, electrodes, and electrolytes. Membrane and electrode modification has improved battery performance to some extent; however, the strong oxidizing and corrosive properties of bromine restrict membrane selection, and electrode modification methods are typically complex and costly, hindering commercialization. Therefore, electrolyte optimization has become an effective strategy for improving battery performance. In particular, the addition of bromine complexing agents (BCAs) to suppress bromine cross-diffusion is a simple, easy-to-implement, and highly operable method. Traditional BCAs (such as 1-methyl-1-ethylpyrrolidine bromide) and Br... (2n+1) - The formed BCA-Br (2n+1) - Molten salts possess high density and strong hydrophobicity, enabling them to separate from the aqueous phase and form an oil phase. However, during battery charge-discharge cycles, this phase separation can lead to the deposition of oil or solid products on the membrane surface, increasing the battery's internal resistance. As the reaction progresses, these products may clog porous electrodes, creating dead reaction zones and severely impairing battery performance, resulting in rapid capacity decay and poor cycle stability in zinc-bromine flow batteries. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide an application of carnitine hydrochloride in a zinc-bromine flow battery electrolyte, a zinc-bromine flow battery electrolyte, and a battery. This invention uses highly hydrophilic carnitine hydrochloride as a bromine complexing agent in a zinc-bromine flow battery electrolyte to form a homogeneous electrolyte, solving the phase separation problem caused by traditional bromine complexing agents. Furthermore, the application of carnitine hydrochloride in the zinc-bromine flow battery electrolyte can suppress bromine cross-diffusion and effectively improve battery cycle stability.

[0005] This invention provides an application of carnitine hydrochloride in the electrolyte of a zinc-bromine flow battery.

[0006] This invention provides a zinc-bromine flow battery electrolyte, comprising an active material, a supporting electrolyte, a bromine complexing agent, and water; The bromine complexing agent is carnitine hydrochloride.

[0007] Preferably, the concentration of the bromine complexing agent in the electrolyte of the zinc-bromine flow battery is 0.1~0.6 mol / L.

[0008] Preferably, the active material includes a positive electrode active material and / or a negative electrode active material, wherein the positive electrode active material is a bromide ion salt and the negative electrode active material is a zinc ion salt.

[0009] Preferably, the bromide salt includes one or more of zinc bromide, potassium bromide, sodium bromide, and ammonium bromide.

[0010] Preferably, the zinc ion salt includes one or more of zinc bromide, zinc chloride, and zinc sulfate.

[0011] Preferably, the concentration of active material in the electrolyte of the zinc-bromine flow battery is 0.5~2 mol / L.

[0012] Preferably, the supporting electrolyte is potassium bromide.

[0013] Preferably, the concentration of the supporting electrolyte in the zinc-bromine flow battery electrolyte is 1~4 mol / L.

[0014] The present invention also provides a zinc-bromine flow battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the electrolyte is the zinc-bromine flow battery electrolyte described in the above technical solution.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides an application of carnitine hydrochloride in the electrolyte of a zinc-bromine flow battery. This invention uses highly hydrophilic carnitine hydrochloride as a bromine complexing agent in the zinc-bromine flow battery electrolyte to form a homogeneous electrolyte, solving the problem of phase separation that is common with traditional bromine complexing agents. Furthermore, the application of carnitine hydrochloride in the zinc-bromine flow battery electrolyte can suppress bromine cross-diffusion and effectively improve the cycle stability of the battery. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The performance data are obtained from electrolyte tests in Examples 1-4 and Comparative Example 1; Figure 2 The results show the long-cycle discharge capacity of the electrolytes in Example 3 and Comparative Examples 1-2; Figure 3 The first charge-discharge curves for the electrolytes of Example 3 and Comparative Example 2 are shown below. Figure 4 The results are the coulombic efficiency obtained from electrolyte tests in Example 3 and Comparative Example 2. Figure 5 The energy efficiency results are those obtained from electrolyte tests in Example 3 and Comparative Example 2. Figure 6 The voltage efficiency results are those obtained from electrolyte tests in Example 3 and Comparative Example 2. Figure 7 The results show the long-cycle discharge capacity of the electrolytes in Example 5 and Comparative Examples 3-4; Figure 8 The first charge-discharge curves are for the electrolytes of Example 5 and Comparative Example 3. Detailed Implementation

[0018] This invention provides an application of carnitine hydrochloride in the electrolyte of a zinc-bromine flow battery.

[0019] In this invention, carnitine hydrochloride (CH) is added to the electrolyte as a bromine complexing agent. Carnitine hydrochloride has hydrophilic hydroxyl and carboxyl groups, and its structural formula is shown below: ; Carnitine hydrochloride (CH), as a hydrophilic bromine complexing agent, can form a homogeneous electrolyte, inhibit the cross-diffusion of bromine, effectively improve the cycle stability of the battery, and solve the problem of phase separation that traditional bromine complexing agents are prone to.

[0020] This invention provides a zinc-bromine flow battery electrolyte, comprising an active material, a supporting electrolyte, a bromine complexing agent, and water; The bromine complexing agent is carnitine hydrochloride.

[0021] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0022] In this invention, the electrolyte of the zinc-bromine flow battery is a positive electrode and / or a negative electrode electrolyte.

[0023] In this invention, the active material includes a positive electrode active material and / or a negative electrode active material. The positive electrode electrolyte contains the positive electrode active material, and the negative electrode electrolyte contains the negative electrode active material. The positive electrode active material is a bromide ion salt, which preferably includes one or more of zinc bromide, potassium bromide, sodium bromide, and ammonium bromide, and more preferably zinc bromide (ZnBr2). The negative electrode active material is preferably a zinc ion salt, which preferably includes one or more of zinc bromide, zinc chloride, and zinc sulfate, and more preferably zinc bromide (ZnBr2).

[0024] In this invention, the concentration of active material in the electrolyte of the zinc-bromine flow battery is preferably 0.5~2 mol / L, specifically 0.5 mol / L, 1 mol / L or 2 mol / L.

[0025] In this invention, the supporting electrolyte is preferably potassium bromide (KBr), and the concentration of the supporting electrolyte in the zinc-bromine flow battery electrolyte is preferably 1~4 mol / L, specifically 1 mol / L, 2 mol / L, 3 mol / L, or 4 mol / L. The supporting electrolyte can improve the ionic conductivity of the electrolyte.

[0026] In this invention, the concentration of the bromine complexing agent in the electrolyte of the zinc-bromine flow battery is preferably 0.1~0.6 mol / L, specifically 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, or 0.6 mol / L. Compared to using 1-methyl-1-ethylpyrrolidine bromide (MEP) as the bromine complexing agent, this invention uses carnitine hydrochloride as the bromine complexing agent, which can form a homogeneous electrolyte, inhibit the cross-diffusion of bromine, and effectively improve the cycle stability of the battery.

[0027] The present invention also provides a zinc-bromine flow battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the electrolyte is the zinc-bromine flow battery electrolyte described in the above technical solution.

[0028] In this invention, the diaphragm is preferably a porous polyethylene membrane or a Nafion 117 membrane.

[0029] In this invention, the zinc-bromine flow battery preferably adopts a symmetrical flow battery structure, specifically: with the separator as the center on both sides of the positive and negative electrodes, the following components are arranged in sequence: positive electrode plate, rubber pad, copper current collector, graphite plate, positive electrode frame, 33×33mm carbon felt, separator, 33×33mm carbon felt, negative electrode frame, graphite plate, copper current collector, rubber pad, and negative electrode plate. The zinc-bromine flow battery is assembled with positive and negative electrode electrolyte storage tanks and a pump through pipelines.

[0030] To further illustrate the present invention, the application of carnitine hydrochloride provided by the present invention in the electrolyte of zinc-bromine flow batteries, the zinc-bromine flow battery electrolyte, and the battery are described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0031] In the embodiments or comparative examples of the present invention, the solvent of the electrolyte is water, and M refers to mol / L; Assembly of a single cell: A symmetrical flow battery structure is adopted. With the membrane material (separator) as the center on both sides of the positive and negative electrodes, the following components are arranged in sequence: positive electrode plate, rubber pad, copper current collector, graphite plate, positive electrode frame, 33×33mm carbon felt, separator, 33×33mm carbon felt, negative electrode frame, graphite plate, copper current collector, rubber pad, and negative electrode plate. The zinc-bromine flow battery is assembled with positive and negative electrolyte storage tanks and a peristaltic pump through pipelines.

[0032] In Examples 1-4 and Comparative Examples 1-2, the porous polyethylene membrane used had a thickness of 800 μm and was sourced from Zhengzhou Youchu New Energy Technology Co., Ltd. The peristaltic pump operates at 60 mL / min. -1 The positive and negative electrolytes are circulated at a certain flow rate. In the charge-discharge test, the capacity cutoff method is used. The electrolyte is charged to 60% SOC (state of charge), with a charging cutoff voltage of 2.4 V and a discharging cutoff voltage of 0.5 V.

[0033] Example 1 The electrolyte consists of 1 M ZnBr2 + 2 M KBr + 0.2 M carnitine hydrochloride (CH), and the diaphragm is a porous polyethylene membrane.

[0034] At 60 mA·cm -2 Charge and discharge tests were conducted, and the average values ​​of coulombic efficiency (CE), energy efficiency (EE), and voltage efficiency (VE) were taken for the first 30 cycles. The values ​​of CE, EE, and VE were 86.56%, 69.16%, and 78.96%, respectively.

[0035] Example 2 The electrolyte consists of 1 M ZnBr2 + 2 M KBr + 0.3 M carnitine hydrochloride (CH), and the diaphragm is a porous polyethylene membrane.

[0036] At 60 mA·cm -2 Charge and discharge tests were conducted, and the average values ​​of coulombic efficiency (CE), energy efficiency (EE), and voltage efficiency (VE) were taken for the first 30 cycles. The values ​​of CE, EE, and VE were 89.74%, 65.91%, and 75.99%, respectively.

[0037] Example 3 The electrolyte consists of 1 M ZnBr2 + 2 M KBr + 0.4 M carnitine hydrochloride (CH), and the diaphragm is a porous polyethylene membrane.

[0038] At 60 mA·cm -2 Charge and discharge tests were conducted, and the average values ​​of coulombic efficiency (CE), energy efficiency (EE), and voltage efficiency (VE) were taken for the first 30 cycles. The values ​​of CE, EE, and VE were 92.57%, 74.79%, and 80.68%, respectively.

[0039] Example 4 The electrolyte consists of 1 M ZnBr2 + 2 M KBr + 0.5 M carnitine hydrochloride (CH), and the diaphragm is a porous polyethylene membrane.

[0040] At 60 mA·cm -2 Charge and discharge tests were conducted, and the average values ​​of coulombic efficiency (CE), energy efficiency (EE), and voltage efficiency (VE) were taken for the first 30 cycles. The values ​​of CE, EE, and VE were 88.74%, 68.03%, and 74.68%, respectively.

[0041] Comparative Example 1 The electrolyte consists of 1 M ZnBr2 + 2 M KBr, and the diaphragm is a porous polyethylene membrane.

[0042] At 60 mA·cm -2 Charge and discharge tests were conducted, and the average values ​​of coulombic efficiency (CE), energy efficiency (EE), and voltage efficiency (VE) were taken for the first 30 cycles. The values ​​of CE, EE, and VE were 76.22%, 64.28%, and 84.93%, respectively.

[0043] Figure 1 The data presented are performance data obtained from electrolyte tests in Examples 1-4 and Comparative Example 1. The data from Examples 1-4 and Comparative Example 1 show that using carnitine hydrochloride (CH) as a bromine complexing agent can effectively improve coulombic efficiency, with the highest efficiency observed at a CH concentration of 0.4 M. This may be because lower CH concentrations result in lower ability to complex polybrominates, while higher CH concentrations enhance polarization, thus reducing voltage efficiency.

[0044] Comparative Example 2 The electrolyte consists of 1 M ZnBr2 + 2 M KBr + 0.4 M 1-methyl-1-ethylpyrrolidine bromide (MEP), and the diaphragm is a porous polyethylene membrane.

[0045] At 60 mA·cm -2 Long-cycle testing will then be conducted.

[0046] Figure 2 For long-cycle discharge capacity results, Figure 3 The first charge-discharge curves are shown, where CH corresponds to Example 3, MEP corresponds to Example 2, and Additive free corresponds to Example 1.

[0047] Example 3 achieved a first-cycle coulombic efficiency of 91.67%, effectively cycling up to 260 cycles without capacity decay. Comparative Example 2 showed a first-cycle coulombic efficiency of only 63.05%, unstable cycling, and continuous capacity decay during operation, failing to cycle beyond 110 cycles. Comparative Example 1 (without a complexing agent) only cycled 20 times before both charge and discharge capacities began to decay. Compared to the addition of the traditional bromine complexing agent 1-methyl-1-ethylpyrrolidine bromide (MEP) and the absence of a bromine complexing agent, the addition of CH in this invention solves the problems of rapid capacity decay and poor cycling stability, and inhibits bromine cross-diffusion.

[0048] Figure 4 The results are the coulombic efficiency obtained from electrolyte tests in Example 3 and Comparative Example 2. Figure 5 The energy efficiency results are those obtained from electrolyte tests in Example 3 and Comparative Example 2. Figure 6 The voltage efficiency results are obtained from electrolyte tests in Example 3 and Comparative Example 2.

[0049] The coulombic efficiency, energy efficiency, and voltage efficiency of Example 3 are stable and better than those of Comparative Example 2 during the cycling process. The coulombic efficiency and energy efficiency of Comparative Example 2 fluctuate more strongly during the cycling process and gradually weaken as the cycling progresses.

[0050] Example 5 The electrolyte consists of 1 M ZnBr2 + 2 M KBr + 0.4 M carnitine hydrochloride (CH), and the diaphragm is a more selective Nafion 117 membrane.

[0051] At 20 mA·cm -2 Long-cycle testing will then be conducted.

[0052] Comparative Example 3 The electrolyte consists of 1 M ZnBr2 + 2 M KBr + 0.4 M 1-methyl-1-ethylpyrrolidine bromide (MEP), and the diaphragm is a more selective Nafion 117 membrane.

[0053] At 20 mA·cm -2 Long-cycle testing will then be conducted.

[0054] Comparative Example 4 The electrolyte consists of 1 M ZnBr2 + 2 M KBr, and the separator is a more selective Nafion 117 membrane.

[0055] At 20 mA·cm -2 Long-cycle testing will then be conducted.

[0056] Figure 7 The results show the long-cycle discharge capacity of the electrolytes in Example 5 and Comparative Examples 3-4. Figure 8 The first charge-discharge curves of the electrolytes in Example 5 and Comparative Example 3 are shown, where CH corresponds to Example 5, MEP corresponds to Comparative Example 3, and Additive free corresponds to Comparative Example 4.

[0057] Example 5 achieved a first-cycle coulombic efficiency of 92.65% and remained effective for 250 cycles without capacity decay. Comparative Example 3 had a first-cycle coulombic efficiency of only 70.95%, exhibited unstable cycling in the early stages, and experienced rapid capacity decay after 150 cycles. Comparative Example 4 (i.e., without complexing agent) showed capacity decay after less than 20 cycles.

[0058] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. Use of carnitine hydrochloride in zinc-bromine flow battery electrolyte.

2. A zinc-bromine flow battery electrolyte characterized in that, The electrolyte comprises an active substance, a supporting electrolyte, a bromine complexing agent and water. The bromine complexing agent is carnitine hydrochloride.

3. The zinc-bromine flow battery electrolyte of claim 2, wherein, The concentration of the bromine complexing agent in the zinc-bromine flow battery electrolyte is 0.1-0.6 mol / L.

4. The zinc-bromine flow battery electrolyte of claim 2, wherein, The active substance comprises a positive active substance and / or a negative active substance, the positive active substance is a bromide salt, and the negative active substance is a zinc ion salt.

5. The zinc-bromine flow battery electrolyte of claim 4, wherein, The bromide salt comprises one or more of zinc bromide, potassium bromide, sodium bromide and ammonium bromide.

6. The zinc-bromine flow battery electrolyte of claim 4, wherein, The zinc ion salt comprises one or more of zinc bromide, zinc chloride and zinc sulfate.

7. The zinc-bromine flow battery electrolyte of claim 2 or 4, wherein, The concentration of the active substance in the zinc-bromine flow battery electrolyte is 0.5-2 mol / L.

8. The zinc-bromine flow battery electrolyte of claim 2, wherein, The supporting electrolyte is potassium bromide.

9. The zinc-bromine flow battery electrolyte of claim 2 or 8, wherein, The concentration of the supporting electrolyte in the zinc-bromine flow battery electrolyte is 1-4 mol / L.

10. A zinc-bromine flow battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The electrolyte is the zinc-bromine flow battery electrolyte according to any one of claims 2-9.

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