High-current-density zinc-bromine flow battery, negative electrode electrolyte and preparation method of high-current-density zinc-bromine flow battery

Abstract

The invention belongs to the field of batteries, and provides a high-current-density long-circulation zinc-bromine flow battery negative electrode electrolyte and battery preparation. The battery comprises a positive electrode, a negative electrode, a diaphragm, positive and negative electrolyte, a current collector and an end plate, the diaphragm is a cation exchange membrane; and the negative electrode electrolyte comprises a metal salt, a supporting electrolyte, an organic carboxylate complexing agent and deionized water. The organic carboxylate complexing agent disclosed by the invention can be adsorbed on a porous electrode, and by increasing zinc deposition sites, inhibiting two-dimensional interface diffusion and promoting zinc mass transfer, zinc dendrites are relieved, and the zinc-bromine flow battery with high current density and long circulation stability is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of zinc-bromine liquid flow batteries, and in particular relates to an aqueous negative electrode electrolyte and a zinc-bromine liquid flow battery. Background Art

[0002] While the use of fossil energy has promoted global development, it has also brought about problems such as environmental degradation and the greenhouse effect. In order to achieve coordinated development of the economy and the environment, my country has vigorously developed new energy sources such as solar energy and wind energy, and has applied them on a large scale in the power sector. However, new energy sources such as solar energy and wind energy have problems with intermittent and fluctuating power generation, which cannot perfectly meet electricity demand. Therefore, there is an urgent need to develop medium- and long-term energy storage technologies.

[0003] Zinc-bromine flow batteries (Zn-Br) hold promise as a medium- to long-term energy storage technology due to their abundant raw materials, low cost, and relatively high energy density. However, uneven zinc deposition on the negative electrode leads to the formation of zinc dendrites, which is particularly severe at high current densities. This affects the battery's cycling stability and limits its practical application. Therefore, developing modification strategies to promote uniform zinc deposition at high current densities is crucial for the development of Zn-Br flow batteries.

[0004] The electrochemical reduction of zinc goes through three processes. First, the zinc ions in the main body of the solution diffuse to the electrode interface through mass transfer. Then the zinc ions are desolvated and reduced to zinc atoms by electrons on the electrode. Finally, the zinc atoms nucleate and grow. Due to the uneven distribution of nucleation sites at the electrode interface and the fact that the electrochemical rate of zinc ions is higher than the diffusion rate, a large concentration polarization is caused, which in turn leads to uneven zinc deposition, resulting in dendrites that affect the battery cycle life. Therefore, we can achieve uniform zinc deposition by regulating one or both of the above processes. At present, strategies have been developed to alleviate zinc dendrites, including electrode modification, diaphragm modification, and electrolyte management.

[0005] In recent years, several innovative approaches to modifying zinc-based flow battery electrodes have demonstrated significant progress. Researchers have used magnetron sputtering to pre-deposit metallic tin (Sn) onto carbon felt, effectively manipulating zinc deposition behavior. The Sn layer provides homogeneous nucleation sites for uniform zinc deposition. Its favorable hydrogen evolution potential suppresses the hydrogen evolution side reaction, reducing the Coulombic efficiency loss caused by hydrogen evolution corrosion. Experimental data show that the cycling stability of the Sn-modified electrode is significantly improved compared to that of pristine carbon felt batteries. Furthermore, researchers have used pulsed laser deposition to construct a bismuth oxide (Bi2O3) functional layer on the carbon felt surface. This modified layer exhibits dual regulatory mechanisms: First, the high nucleation site density of Bi2O3 improves the spatial uniformity of zinc deposition during the initial stages, reducing the local electric field strength and thus the hydrogen evolution reaction; second, the strong Bi-Zn interaction inhibits the surface migration of zinc atoms, promoting the formation of a dense deposition layer. At a high current density of 60 mA cm⁻², the Bi2O3-modified system achieved 200 stable cycles, far exceeding the lifespan of the control.

[0006] In zinc-bromine flow battery systems, the separator is not only a core component that maintains the ion exchange pathway between the positive and negative electrodes but also plays a crucial role in preventing physical contact and short circuits between the electrodes. Its physical and chemical properties have a crucial impact on system performance. Currently, mainstream commercial separators are mainly cation-selective membranes and porous dielectric membranes. Research has shown that because the electrode-separator interface is a thermodynamically advantageous region for preferential zinc deposition, the metal deposition morphology can be manipulated through separator interface engineering. One research work innovatively employed a polyethersulfone / sulfonated polyetheretherketone (PEEK) dual-layer composite porous matrix and introduced a montmorillonite-modified layer on its surface. This design is innovative in two ways: the montmorillonite material's high mechanical stability and surface negative charge create a synergistic effect—its electrostatic hysteresis weakens the uneven migration of zinc ions parallel to the separator, significantly suppressing dendrite formation. Furthermore, the material's stress-strain resistance effectively mitigates damage to the separator caused by dendrites resulting from uneven zinc deposition during cycling. Furthermore, a research team has proposed the application of a polyethylene glycol (PEG)-functionalized coating on the interface of a conventional polyolefin porous separator. Experiments have confirmed that the modified layer optimizes the deposition process through two physicochemical mechanisms: on the one hand, the complexation effect between the PEG group and Zn²+ can regulate the concentration gradient distribution of metal ions near the interface and promote uniform nucleation; on the other hand, the steric hindrance effect generated by the high-density PEG chains can limit the surface two-dimensional diffusion path of the deposited zinc crystal nuclei, reduce the generation of zinc clusters, and thus realize a high-areal-capacity zinc-based liquid flow battery.

[0007] Despite breakthroughs in electrode and separator modification, these processes require pre-modification of the electrodes or separators, which is complex and costly. Furthermore, the modified layer can easily fall off or be covered by deposited zinc during battery cycling, making subsequent zinc deposition impossible to control. Electrolytes, on the other hand, connect electrodes and transport ions, so regulating them can more effectively mitigate zinc dendrites.

[0008] At present, the main electrolyte management methods are to use high-concentration electrolyte or add organic additives. For example, some research uses 1 M Zn(TFSI)2 and 20 M LiTFSI as electrolyte. The high concentration of TFSI anions will participate in the solvation structure of zinc ions to form Zn(TFSI)6 4- Complexes, thereby reducing the amount of solvent water, and then slowing down the dehydrogenation reaction, which leads to a decrease in the coulombic efficiency of the battery and promotes the formation of zinc dendrites. However, high-concentration electrolytes will reduce the conductivity of the solution, resulting in severe polarization, affecting its application at high current density, and adding low-concentration additives can effectively avoid this. For example, some researchers have achieved uniform deposition of zinc by adding D-arabinose (DA) to the blank electrolyte. Experimental and theoretical calculations show that DA additives can be preferentially adsorbed on the electrode, thereby increasing the initial deposition sites and promoting uniform deposition of zinc. Battery test results show that compared with the blank sample symmetrical battery, the symmetrical battery containing DA additives has a higher capacitance at 10 mA cm -2 Under the test conditions, it still ran stably for more than 700 hours, and the cycle life was greatly improved. In addition, some researchers introduced 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) into the electrolyte as an electrolyte additive to achieve uniform distribution of zinc ions. The research work found that the 18-crown-6 additive increased the migration number of zinc ions, thereby promoting the uniform distribution of zinc ion concentration at the electrode interface and stabilizing the electric field at the zinc negative electrode interface. The experimental results showed that the 18-crown-6 additive had a significant effect on the precipitation cell at 1 mA cm -2 The battery can be stably cycled for more than 1700 h at a current density of 100 mA cm, while the blank symmetric battery fails in less than 100 h. -2 However, little research has been conducted on achieving uniform zinc deposition. This is likely because regulating only one stage of the zinc deposition process is insufficient for achieving uniform zinc deposition at high current densities. Therefore, it is necessary to develop novel additives that can simultaneously optimize zinc deposition and mass transfer, thereby achieving long cycle life and stable zinc-bromine flow batteries at high current densities. Summary of the Invention In order to alleviate the generation of zinc dendrites under high current density, the present invention provides an aqueous negative electrode electrolyte and a zinc-bromine flow battery preparation.

[0009] To achieve the above object, the present invention adopts the following technical solutions: A high current density zinc-bromine flow battery comprises a positive electrode, a negative electrode, a separator, positive and negative electrode electrolytes, a current collector, and an end plate. The positive and negative electrodes are porous electrodes, the separator is a cation exchange membrane, the negative electrode electrolyte comprises zinc salt, potassium salt and organic carboxylate additives, the current collector is a titanium plate, and the end plate is a stainless steel end plate.

[0010] Furthermore, the positive and negative electrodes are carbon felt electrodes, and the size of the carbon felt is 3*3-5*5 cm.

[0011] Furthermore, the diaphragm is Nafion212.

[0012] A negative electrode electrolyte for a high current density zinc-bromine flow battery comprises a zinc salt, a potassium salt and an additive.

[0013] Furthermore, the zinc salt concentration is 1-4 mol / L.

[0014] Furthermore, the potassium salt is potassium bromide.

[0015] Furthermore, the potassium salt concentration is 2-5 mol / L.

[0016] Furthermore, the additive is an organic carboxylate compound; the organic carboxylate compound is diethylenetriamine pentaacetic acid pentasodium (DTPA-Na).

[0017] Furthermore, the concentration of the additive is 0.01-0.1 mol / L.

[0018] Furthermore, the concentration of the additive is 0.05 mol / L.

[0019] A method for preparing a zinc-bromine flow battery comprises the following steps: Preparation of positive and negative electrodes: Cut the carbon felt into a shape with a length and width of 3*3 cm.

[0020] Preparation of negative electrode electrolyte: DTPA-Na was dissolved in an aqueous solution containing zinc bromide and potassium bromide.

[0021] The method for preparing the negative electrode electrolyte of the present invention comprises the following steps: Dissolve 112.61 g ZnBr2 and 80.25 g KBr in 100 mL deionized water, then stir evenly, and dilute to 250 mL with a volumetric flask to obtain a Blank electrolyte; dissolve 112.61 g ZnBr2, 80.25 g KBr and 1.25815-12.5815 g DTPA-Na in 100 mL deionized water, then stir evenly, and dilute to 250 mL with a volumetric flask to obtain electrolytes containing different concentrations of DTPA-Na.

[0022] Battery Assembly: Assemble the end plates, current collectors, positive and negative electrodes, and separator in sequence. Then, circulate the electrolyte stored in the reservoir into the battery via a peristaltic pump. Connect the battery to the Xinwei test system and perform constant current charge and discharge tests at room temperature in a fume hood. Unless otherwise specified, charging is cutoff by capacity, and discharging is cutoff by voltage.

[0023] Compared with the existing technology, the present invention has the following beneficial effects: This invention proposes a high-current-density, long-cycle zinc-bromine flow battery anode electrolyte and a battery preparation method. These solutions effectively mitigate zinc dendrite growth at high current densities and improve battery cycle stability. By introducing diethylenetriamine pentaacetic acid sodium salt (DTPA-Na) as a highly efficient and multifunctional additive, the invention offers the following advantages: (1) DTPA-Na participates in the solvation structure of zinc ions, and then DTPA-Zn species are preferentially adsorbed at the electrode interface, increasing the zinc deposition sites; (2) During zinc deposition, DTPA adsorbed on the interface can restrain the two-dimensional diffusion of zinc and reduce the formation of zinc clusters; (3) DTPA has a strong interaction with zinc ions and can optimize the concentration gradient at the electrode interface. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The cyclic voltammograms of the examples of the present invention and the comparative example are shown in FIG.

[0024] Figure 2 3 and 4 are zinc deposition morphologies of the embodiments of the present invention and the comparative example.

[0025] Figure 3 The XRD patterns of the embodiments of the present invention and the comparative examples are shown in FIG.

[0026] Figure 4 It is the CA diagram of the embodiment of the present invention and the comparative example.

[0027] Figure 5 The NMR and XPS diagrams of the examples of the present invention and the comparative examples are shown.

[0028] Figure 6 COMSOL simulations of the embodiments of the present invention and comparative examples.

[0029] Figure 7 The symmetrical battery cycle performance of the embodiment of the present invention and the comparative example.

[0030] Figure 8 The figure shows the cycle performance of zinc-bromine flow batteries of the embodiments of the present invention and the comparative example. Specific implementation methods The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope of the present invention and its application.

[0031] An embodiment of the present invention provides a negative electrode electrolyte and battery preparation for a high current density long cycle zinc-bromine liquid flow battery, including positive and negative electrodes, a separator, an electrolyte, a current collector, and an end plate. The positive and negative electrodes are 3*3 cm carbon felt electrodes, the separator is Nafion212, the current collector is a titanium plate, the end plate is a stainless steel plate, and the negative electrode electrolyte includes a zinc salt, a potassium salt, and an organic carboxylate additive.

[0032] The present invention provides a negative electrode electrolyte and battery preparation for high-current-density, long-cycle zinc-bromine flow batteries. To address the problem of uneven zinc deposition at high current densities, the present invention introduces pentasodium diethylenetriamine pentaacetate (DTPA-Na) as an electrolyte additive. DTPA-Na participates in the solvation structure of zinc ions, forming DTPA-Zn species that subsequently adsorb on the electrode, increasing initial deposition sites. During charging, DTPA adsorbed on the electrode inhibits two-dimensional zinc diffusion at the interface and the formation of zinc clusters. DTPA adsorbed on the electrode also promotes zinc mass transfer. Both zinc-symmetric batteries and zinc-bromine flow batteries using electrolytes containing this additive exhibit excellent cycling performance at high current densities. This invention provides new insights for the practical application of high-current-density, long-cycle zinc-bromine flow batteries.

[0033] The following further describes specific examples and comparative examples of the present invention.

[0034] Example 1 Weigh 112.61 g ZnBr2, 89.25 g KBr and 6.29 g DTPA-Na in deionized water to prepare a 250 mL mixed solution to obtain the zinc-bromine flow battery electrolyte for use.

[0035] Example 2 Weigh 112.61 g ZnBr2, 89.25 g KBr and 3.75 g DTPA-Na in deionized water to prepare 250 mL of a mixed solution to obtain the zinc-bromine flow battery electrolyte for later use.

[0036] Example 3 Weigh 112.61 g ZnBr2, 89.25 g KBr and 8.81 g DTPA-Na in deionized water to prepare 250 mL of a mixed solution to obtain the zinc-bromine flow battery electrolyte for later use.

[0037] Comparative Example 4 Weigh 112.61 g ZnBr2 and 89.25 g KBr in deionized water to prepare 250 mL of a mixed solution to obtain the zinc-bromine flow battery electrolyte for later use.

[0038] Performance Testing Cyclic voltammetry (CV) testing: A glassy carbon electrode was used as the working electrode, a platinum wire electrode as the counter electrode, and a saturated Ag / AgCl solution as the reference electrode. The prepared electrolytes from each example and comparative example were poured into a beaker and connected to an electrochemical workstation. The voltage window was -1.5 to 0 V, and the scan rate was 50 mV / s.

[0039] Figure 1 The cyclic voltammograms of Example 1 and Comparative Example 4 show that after the introduction of the DTPA-Na additive, the reduction peak potential of zinc shifts positively, while the oxidation peak potential shifts negatively, indicating that the presence of DTPA-Na improves the reversibility of zinc deposition / stripping, which is beneficial to the subsequent battery cycle stability.

[0040] Morphology characterization of deposited zinc (SEM): SEM characterization of zinc deposited on carbon felt was performed after charging with a zinc symmetric battery.

[0041] Figure 2 The morphology of zinc deposited on carbon felt after charging the battery using the electrolytes of Example 1 and Comparative Example 4 is compared. The zinc deposited in the comparative example exhibits a disordered flaky structure, while the zinc deposited in the example exhibits a layered stacked structure, which facilitates uniform zinc deposition.

[0042] Crystallographic analysis of deposited zinc (XRD): XRD analysis of zinc deposited on carbon felt after charging with a zinc symmetric battery Figure 3 This figure compares the XRD results of zinc deposited on carbon felt after charging the battery using the electrolytes of Example 1 and Comparative Example 4. The (002) / (101) ratio ranges from 0.37 to 0.98, indicating that the presence of the DTPA-Na additive causes zinc to preferentially deposit on the (002) crystal plane.

[0043] Chronoamperometry (CA) test: zinc symmetric cells were assembled and the electrolytes of the embodiment and comparative example were used at -0.2V (Vs. Zn 2+ CA test was carried out at an overpotential of 1.5 % (Zn / 2).

[0044] Figure 4The CA test results, using the electrolyte in Comparative Example 4, show that the current increases with time, indicating unrestricted two-dimensional interfacial diffusion, which leads to the formation of zinc clusters and, in turn, zinc dendrites. In contrast, the current in Example 1 remains stable, indicating that the additive effectively limits two-dimensional interfacial diffusion, facilitating uniform zinc deposition.

[0045] NMR and XPS analysis: The electrolytes of the examples and comparative examples were subjected to NMR analysis, and the carbon felt was immersed in the electrolytes of the examples and comparative examples, and then subjected to XPS analysis.

[0046] Figure 5 a is 1 The H NMR results showed that after adding the additive, the nuclear magnetic peak of D2O moved to the high field. This was because the additive participated in the solvation structure of zinc ions, subsequently producing more free water and enhancing the proton shielding effect. Figure 5 b is the XPS analysis. The Zn 2P peak of the carbon felt immersed in the electrolyte of the embodiment is shifted positively by 0.5 eV compared with the comparative example, which indicates that the species adsorbed on the carbon felt is DTPA-Zn. In addition, the Zn signal is stronger than that of the comparative example, indicating that the concentration of zinc ions adsorbed on the carbon felt is higher, which is beneficial to increase the initial deposition sites of zinc.

[0047] COMSOL simulation: Simulation of the change of zinc ion concentration at the electrode interface with time during the charging process of carbon felt modified with and without DTPA-Na.

[0048] Figure 6 ab are COMSOL simulation comparisons of unmodified and modified carbon felt, respectively, indicating that the presence of additives is beneficial to promoting the mass transfer of zinc ions and reducing the concentration gradient of zinc ions on the electrode interface.

[0049] Zn||Zn symmetric cell: The electrolytes of Example 1 and Comparative Example 4 were used to assemble symmetric cells, and then the electrolytes were charged at 80 mA / cm 2 and 20 mAh / cm 2 Long cycle test was performed.

[0050] Figure 7 The symmetrical battery of the electrolyte of Example 4 and Example 1 has a voltage curve fluctuation at 185 cycles compared to the comparative example, while the symmetrical battery of the example remains stable within 530 cycles, indicating that the presence of the additive is beneficial to improving the battery stability.

[0051] Zinc-bromine flow battery: The zinc-bromine flow battery was assembled with the electrolytes of Example 1 and Comparative Example 4, and then the electrolytes were charged at 80 mA / cm 2 and 20 mAh / cm 2 Long cycle test was performed.

[0052] Figure 8 ab are symmetrical batteries with electrolytes of Comparative Example 4 and Example 1, respectively. Compared with the comparative example which had a short circuit at 70 cycles, the battery of the example remained stable within 320 cycles, indicating that the presence of the additive is conducive to improving the battery stability.

[0053] The above results show that the zinc-bromine flow battery negative electrode electrolyte containing DTPA-Na additive and the battery preparation method provided by the present invention can effectively improve the cycle stability of the battery and have good application prospects.

[0054] The above describes the basic principles, main features, and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the foregoing embodiments. The foregoing embodiments and description merely illustrate the principles of the present application. Various changes and modifications are possible without departing from the spirit and scope of the present application, and such changes and modifications fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the appended claims and their equivalents.

Claims

1. A high current density zinc-bromine flow battery, characterized in that: It includes a positive electrode, a negative electrode, a diaphragm, positive and negative electrode electrolytes, a current collector and an end plate; the positive and negative electrodes are porous electrodes; the diaphragm is a cation exchange membrane; the negative electrode electrolyte includes zinc salt, potassium salt and additives; the current collector is a titanium plate; and the end plate is a stainless steel end plate.

2. A high current density zinc-bromine flow battery according to claim 1, characterized in that: The porous electrode is carbon felt, and the size of the carbon felt is 3*3-5*5 cm.

3. A high current density zinc-bromine flow battery according to claim 1, characterized in that: The cation exchange membrane is Nafion212.

4. A negative electrode electrolyte for a high current density zinc-bromine flow battery according to any one of claims 1 to 3, characterized in that: Includes zinc salts, potassium salts and additives.

5. The negative electrode electrolyte according to claim 4, wherein: The zinc salt is zinc bromide; the concentration of the zinc salt is 1-4 mol / L.

6. The negative electrode electrolyte according to claim 4, wherein: The potassium salt is potassium bromide; the concentration of the potassium salt is 2-5 mol / L.

7. The negative electrode electrolyte according to claim 4, characterized in that The additive is an organic carboxylate compound; the organic carboxylate compound is diethylenetriamine pentaacetic acid pentasodium (DTPA-Na).

8. The negative electrode electrolyte of the zinc-bromine flow battery according to claim 1, wherein The concentration of the additive is 0.01-0.1 mol / L.

9. The negative electrode electrolyte according to claim 4, characterized in that The concentration of the additive is 0.05 mol / L.

10. The method for preparing a negative electrode electrolyte according to any one of claims 4 to 9, wherein: The steps include: Dissolve ZnBr2 and KBr in deionized water, then stir evenly, and dilute to 250 mL with a volumetric flask to obtain a Blank electrolyte; dissolve ZnBr2, KBr and DTPA-Na in deionized water, then stir evenly, and dilute to 250 mL with a volumetric flask to obtain electrolytes containing different concentrations of DTPA-Na.

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