Application of acetylurea in neutral zinc-manganese flow battery, positive electrode electrolyte of neutral zinc-manganese flow battery and battery

Abstract

The invention relates to the field of batteries, and discloses application of acetylurea in a neutral zinc-manganese flow battery, a positive electrode electrolyte of the neutral zinc-manganese flow battery and the battery. According to the invention, acetylurea is added into the positive electrode electrolyte of the neutral zinc-manganese flow battery, and a dynamic hydrogen bond network is formed between molecules of acetylurea and water molecules while the acetylurea regulates and controls the deposition behavior of manganese, so that the microstructure and interface properties of the electrolyte are further optimized, and ion migration and charge transfer are promoted together; and the problems of low intrinsic conductivity and active substance loss caused by manganese deposition are effectively improved. Under the current density of 20 mA cm, the zinc-manganese flow battery adopting the positive electrode electrolyte provided by the invention can realize coulombic efficiency gt after 360 times of circulation; and the energy efficiency is stabilized to be more than 78%.

Description

Technical Field

[0001] This invention relates to the field of batteries, specifically to the application of acetourea in neutral zinc-manganese flow batteries, as well as the positive electrode electrolyte and battery of neutral zinc-manganese flow batteries. Background Technology

[0002] Neutral zinc-manganese flow batteries, as an important branch of aqueous flow batteries, are considered one of the most promising technologies for long-term energy storage due to their resource advantages, intrinsic safety characteristics, environmental friendliness, and theoretical energy density. However, despite the significant potential of zinc-manganese flow batteries in recent years, the commercialization of neutral zinc-manganese flow batteries still faces the following core bottlenecks: the battery operates in a neutral pH environment, but the intermediate product Mn³⁺ generated under these conditions undergoes a spontaneous disproportionation reaction, as follows:

[0003] This reaction not only directly consumes high-valence Mn³⁺, but also generates additional dead manganese precipitate on the electrode surface, forming a vicious cycle of active material consumption and deposition layer deterioration.

[0004] Traditional systems suppress Mn³⁺ disproportionation by adding complexing agents, but the strong coordination between the complexing agent and Mn²⁺ simultaneously hinders Mn²⁺ oxidation, leading to a 15%-20% decrease in charging capacity. The Mn²⁺ oxidation reaction occurring at the positive electrode during charging is as follows:

[0005] The generated MnO2 deposit layer has two major defects: First, its intrinsic conductivity is low, which leads to a surge in ohmic polarization on the electrode surface; second, the deposit layer has a loose structure, and only a portion of the MnO2 can be effectively dissolved during discharge. The undissolved dead manganese adheres to the electrode surface in the form of insulating particles, causing permanent loss of active material. Summary of the Invention

[0006] This invention aims to overcome the problem of MnO2 deposition caused by the oxidation of Mn²⁺ in existing additives, and provides an application of acetourea in neutral zinc-manganese flow batteries, as well as the positive electrode electrolyte and the battery itself. By adding acetourea to the positive electrode electrolyte of a neutral zinc-manganese flow battery, this invention significantly improves the aforementioned problems.

[0007] To achieve the above objectives, the first aspect of this invention provides an application of acetourea in a neutral zinc-manganese flow battery. While regulating manganese deposition behavior, the dynamic hydrogen bond network formed between acetourea molecules and water molecules further optimizes the microstructure and interfacial properties of the electrolyte, jointly promoting ion migration and charge transfer, effectively improving the problems of low intrinsic conductivity and loss of active material caused by manganese deposition.

[0008] Preferably, the acetourea is an additive used as the positive electrode electrolyte in a neutral zinc-manganese flow battery.

[0009] A second aspect of this invention provides a positive electrode electrolyte for a neutral zinc-manganese flow battery, wherein the positive electrode electrolyte comprises a solvent, a solute, and an additive, wherein the additive is acetylurea. By adding acetylurea to the positive electrode electrolyte, the dynamic hydrogen bond network formed between acetylurea molecules and water molecules, while regulating manganese deposition behavior, further optimizes the microstructure and interfacial properties of the electrolyte, jointly promoting ion migration and charge transfer, and effectively improving the problems of low intrinsic conductivity and loss of active material caused by manganese deposition.

[0010] Preferably, the concentration of acetylurea is 0.05-0.1 mol / L, based on the total amount of the positive electrode electrolyte. The concentration of acetylurea can be 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, or any value between any two of these values.

[0011] Preferably, the solute comprises a manganese salt and a supporting electrolyte, wherein the supporting electrolyte comprises potassium ions and / or sodium ions. Using the above scheme, the active manganese salt, the supporting electrolyte, and the specific functional additive acetourea can form a synergistic effect at the molecular level, fundamentally improving the reversibility and kinetic performance of the Mn²⁺ / MnO₂ electrochemical process on the positive electrode side. Specifically, the manganese salt provides the active material, the supporting electrolyte provides the conductive channel, improves the conductivity of the electrolyte and maintains the osmotic pressure balance between the positive and negative electrodes, and acetourea regulates manganese deposition. Thus, the electrolyte provided by this invention achieves a performance breakthrough through the synergistic mechanism of its components, specifically manifested in the following aspects: (1) Acetourea undergoes a mild coordination reaction with Mn²⁺ in the electrolyte. This dynamic coordination effect has two advantages: first, it regulates the nucleation and growth process of MnO2 at the atomic scale, inducing the formation of a more porous and conductive deposition layer structure, which facilitates complete dissolution during discharge and effectively inhibits the loss of active material and capacity decay caused by the accumulation of dead manganese; second, by partially occupying the coordination sites of Mn²⁺, it slows down the formation and disproportionation reaction rate of intermediate valence state Mn³⁺, and improves the controllability of the reaction pathway.

[0012] (2) The supporting electrolyte not only effectively prevents acidic or alkaline corrosion of battery current collectors and other components, extending equipment life, but more importantly, it provides an ideal and stable reaction window for the Mn²⁺ / MnO2 redox couple. At the same time, alkali metal ions such as K⁺ and / or Na⁺ ensure that the electrolyte has excellent ionic conductivity, guaranteeing the ion transport efficiency of the battery under high-rate charge and discharge conditions and reducing ohmic polarization.

[0013] This application also unexpectedly discovered that the active manganese salt, supporting electrolyte, and acetourea additive do not simply have a cumulative effect, but rather produce a significant synergistic effect. Experiments showed that when the supporting electrolyte concentration is below 1 mol / L (e.g., 0.5 mol / L in Example 6), insufficient ionic conductivity significantly affects battery performance, further demonstrating the crucial role of the component concentration ratio in the synergistic mechanism. While regulating manganese deposition behavior, acetourea, through the dynamic hydrogen bond network formed between its molecules and water molecules, further optimizes the electrolyte's microstructure and interfacial properties, jointly promoting ion migration and charge transfer. This multi-component synergistic mechanism is the core of achieving long cycle life and high rate performance in batteries.

[0014] Preferably, the potassium ions are derived from one or more of potassium sulfate, potassium chloride, and potassium nitrate.

[0015] This application does not restrict the source of sodium ions; any commonly used sources in the field are acceptable, such as sodium chloride, sodium sulfate, sodium nitrate, etc.

[0016] Preferably, the concentration of the supporting electrolyte is 0.5-3.0 mol / L, based on the total amount of the positive electrode electrolyte.

[0017] Preferably, the concentration of the supporting electrolyte is 1-2.5 mol / L, based on the total amount of the positive electrode electrolyte. The concentration of the supporting electrolyte can be 0.5 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 3 mol / L, or any value between any two of these values.

[0018] Preferably, the concentration of the manganese salt is 0.2-0.5 mol / L, based on the total amount of the positive electrode electrolyte. The concentration of the manganese salt can be 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, or any value between any two of these values.

[0019] Preferably, the manganese salt is selected from one or more of manganese sulfate, manganese chloride, and manganese acetate.

[0020] Preferably, the solvent is deionized water.

[0021] Preferably, based on the total amount of hydrogen bonds in the positive electrode electrolyte, the OH stretching vibration peak in the electrolyte is located at 3000-3200 cm⁻¹. -1 The amount of strong hydrogen bonds is not less than 28%, preferably not less than 30%, more preferably 30-31%, and the OH stretching vibration peak is located at 3400-3600 cm⁻¹. -1 The amount of weak hydrogen bonds does not exceed 68%.

[0022] A third aspect of this invention provides a neutral zinc-manganese flow battery, comprising the positive electrode electrolyte described in the second aspect of this invention. The battery provided by this application significantly improves cycle stability and rate performance, offering an efficient, economical, and environmentally friendly solution to address the bottlenecks in the commercial application of zinc-manganese systems.

[0023] The electrolyte provided by this invention has the following advantages compared with the prior art: (1) The present invention designs an electrolyte additive system in a targeted manner. Its core mechanism is that acetylurea dynamically regulates the deposition morphology and electronic structure of manganese dioxide through reversible insertion and extraction.

[0024] (2) The neutral zinc-manganese redox flow battery provided by the present invention has multiple advantages in engineering applications: the electrolyte system avoids highly toxic components, the additives are low-cost and easy to prepare on a large scale, and there is no risk of combustion or explosion during the operation of the entire battery, thus achieving the technical characteristics of being green, pollution-free, low-cost, safe and environmentally friendly.

[0025] At 20mA cm - At current density, zinc-manganese redox flow batteries using this electrolyte can achieve a coulombic efficiency of >98.3% after 360 cycles, with an energy efficiency stable at over 78%. Attached Figure Description

[0026] Figure 1 A schematic diagram of the assembled battery system; Figure 2 Electron micrographs of the electrode deposition microstructure: (a) Neutral zinc-manganese flow batteries without acetourea after 50 μm and (b) 100 μm cycles; (c) Neutral zinc-manganese flow batteries with acetourea added to the positive electrode electrolyte after 50 μm and (d) 100 μm cycles. Figure 3 For 20mA cm -2 Current density, charging to 10 mAh cm⁻¹ -2 Figure 1 shows the cycle performance results of neutral zinc-manganese flow batteries with and without acetourea under the specified conditions. Figure 4 For 10-60 mA cm -2 Current density, 10 mAh cm⁻¹-2 Figure 1 shows the coulombic efficiency and energy efficiency results of rate performance tests on neutral zinc-manganese flow batteries with and without acetourea at a fixed areal capacity. Figure 5 For 10-60 mA cm -2 Current density, 10 mAh cm⁻¹ -2 The time-voltage results of rate performance testing of neutral zinc-manganese flow batteries with and without acetourea at a fixed areal capacity are shown in the figure. Figure 6 The percentage of hydrogen bond network in electrolytes with and without acetourea. Detailed Implementation

[0027] The specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] Furthermore, the term "and / or" in the specification and claims is used to describe the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0030] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0031] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the test methods and testing equipment used in the following embodiments are conventional test methods and testing equipment in the art.

[0032] Example 1 Weigh out 1.6901 g of manganese sulfate monohydrate, 0.2041 g of acetylurea, and 2.982 g of potassium chloride, dissolve them in deionized water, mix them in a beaker, and then pour the mixture into a 20 ml volumetric flask and mix thoroughly to obtain the positive electrode electrolyte. The concentration of manganese sulfate is 0.5 mol / L, the concentration of acetylurea is 0.1 mol / L, and the concentration of potassium chloride is 2 mol / L (to ensure that the osmotic pressure of the positive and negative electrodes is consistent).

[0033] Example 2 Weigh out 0.3380 g of manganese sulfate monohydrate, 0.1020 g of acetylurea and 3.7275 g of potassium chloride, dissolve them in deionized water and mix in a beaker. Then pour the mixture into a 20 ml volumetric flask and mix thoroughly to obtain the positive electrode electrolyte. The concentration of manganese sulfate is 0.1 mol / L, the concentration of acetylurea is 0.05 mol / L and the concentration of potassium chloride is 2.5 mol / L.

[0034] Example 3 Weigh out 1.2584 g of manganese chloride tetrahydrate, 0.2041 g of acetylurea and 2.982 g of potassium chloride, dissolve them in deionized water and mix in a beaker. Then pour the mixture into a 20 ml volumetric flask and mix thoroughly to obtain the positive electrode electrolyte. The concentration of manganese chloride is 0.5 mol / L, the concentration of acetylurea is 0.1 mol / L and the concentration of potassium chloride is 2 mol / L.

[0035] Example 4 Weigh out 1.7302 g of anhydrous manganese acetate, 0.2041 g of acetylurea and 2.982 g of potassium chloride, dissolve them in deionized water and mix in a beaker. Then pour the mixture into a 20 ml volumetric flask and mix thoroughly to obtain the positive electrode electrolyte. The concentration of manganese acetate is 0.5 mol / L, the concentration of acetylurea is 0.1 mol / L and the concentration of potassium chloride is 2 mol / L.

[0036] Example 5 Weigh out 1.6901 g of manganese sulfate monohydrate, 0.2041 g of acetylurea and 2.3376 g of sodium chloride, dissolve them in deionized water and mix in a beaker. Then pour the mixture into a 20 ml volumetric flask and mix thoroughly to obtain the positive electrode electrolyte. The concentration of manganese sulfate is 0.5 mol / L, the concentration of acetylurea is 0.1 mol / L and the concentration of sodium chloride is 2 mol / L.

[0037] Example 6 The procedure was carried out as described in Example 1, except that 0.7455 g of potassium chloride was weighed, thereby increasing the K content in the positive electrode electrolyte. + The concentration is 0.5 mol / L.

[0038] Example 7 The procedure was carried out as described in Example 1, except that 5.2185 g of potassium chloride was weighed, thereby increasing the K content in the positive electrode electrolyte. + The concentration was 3.5 mol / L.

[0039] Comparative Example 1 The procedure was carried out in accordance with Example 1, except that acetylurea was not added to the neutral zinc-manganese flow battery.

[0040] Test case Assembled into a battery, the principle of the battery is as follows: Figure 1 As shown. A neutral zinc-manganese redox flow battery system is constructed based on the positive electrode electrolyte prepared according to the present invention. The core structure of this system consists of the following functional units: a storage tank for storing the negative electrode electrolyte (denoted as storage tank 1), a storage tank for storing the positive electrode electrolyte (denoted as storage tank 2), a peristaltic pump for driving the circulation of the negative electrode electrolyte (denoted as peristaltic pump 3), a peristaltic pump for driving the circulation of the positive electrode electrolyte (denoted as peristaltic pump 4), a membrane assembly for isolating ion conduction from the electrolyte (denoted as membrane 5), a negative electrode (denoted as electrode 6) and a positive electrode (denoted as electrode 7) for undertaking electrochemical reactions.

[0041] The 20ml positive electrode electrolyte storage tank 2 prepared in this application contains the positive electrode electrolyte formulated according to the present invention. Its composition includes a manganese salt as an active material, acetylurea to regulate the hydrogen bond network of the electrolyte solution, and a supporting electrolyte that plays a role in ion conduction and osmotic pressure regulation. The supporting electrolyte enhances the electrolyte conductivity by providing migrating ions and maintains the osmotic pressure balance between the positive and negative electrode electrolytes using the principle of ion strength matching, ensuring the stability of the electrolyte volume and ion environment during battery cycling. 20 ml of negative electrode electrolyte is stored in negative electrode electrolyte storage tank 1. The formulation is an aqueous solution system of 0.5 mol / L zinc acetate and 2 mol / L potassium chloride. The preparation process of this negative electrode electrolyte is as follows: accurately weigh 1.835 g of high-purity zinc acetate (purity ≥99.0%) and 2.982 g of potassium chloride (analytical grade) and transfer them to a clean beaker; add an appropriate amount of deionized water to dissolve them. After the solid is completely dispersed, transfer the solution to a 20 mL volumetric flask; rinse the beaker repeatedly with deionized water and transfer the washings to the volumetric flask, and finally dilute to the mark; achieve uniform mixing of the system by vortexing or magnetic stirring to complete the preparation of the negative electrode electrolyte.

[0042] Both the negative and positive electrodes of this battery system utilize carbon felt as the electrocatalyst and current conduction carrier, with an effective reaction area of ​​3 cm × 3 cm. The membrane assembly used to separate the positive and negative electrolytes employs a commercially available Nafion 115 proton exchange membrane. The processing flow is as follows: (1) Acid treatment: The diaphragm is completely immersed in 1M sulfuric acid solution and reacted in a constant temperature water bath at 80℃ for 1 hour to remove inorganic impurities and activate the surface hydroxyl groups. (2) Water washing: After taking it out, rinse it repeatedly with deionized water at least 3 times until the pH of the rinsing solution is ≈7; (3) Oxidation treatment: Transfer to 5% hydrogen peroxide solution and treat at 80°C for 1 hour to decompose organic pollutants; (4) Alkali treatment: Place in 1M potassium hydroxide / sodium hydroxide solution and treat at 80℃ for 1 hour to neutralize residual oxidants and adjust surface charge density. After all steps are completed, rinse with deionized water until neutral for later use. The membrane has a geometric dimension of 4 cm × 4 cm and its function is based on the selective permeation principle of sulfonic acid groups: on the one hand, it realizes proton (H⁺) conduction to maintain charge balance; on the other hand, it uses the microporous structure of the membrane to limit cross-contamination of active materials and ensure the long-term cycle stability of the battery.

[0043] During battery operation, the electrolyte on the positive electrode side is delivered to the reaction site of the positive electrode 7 via a peristaltic pump 4. The active materials in the positive electrode electrolyte undergo corresponding electrochemical reactions on the electrode surface, and the reaction residue is also returned to the positive electrode electrolyte storage tank 2 via a reflux pipeline. The circulation process of the negative electrode electrolyte is the same as that of the positive electrode. Because a membrane 5 is set between the positive and negative electrodes, only protons (H⁺) or supporting electrolyte ions (K⁺ / Na⁺) are allowed to pass through, thus physically isolating the positive and negative electrode electrolytes and preventing direct mixing of active materials that could lead to side reactions. This provides a stable ionic environment for the continuous electrochemical reaction.

[0044] 1. Battery systems were assembled using electrolytes from Example 1 and Comparative Example 1, respectively. Charge-discharge performance tests were conducted on the batteries at room temperature, starting with a 5mA cm⁻¹ charge / discharge test. -2 The current is used for constant current charging until the capacity reaches 2mAh cm⁻¹. -2 Then at 5mAcm -2 A constant current discharge was applied until the voltage reached 0.4V, then a 20mA cm⁻¹ discharge was applied. -2 The current is constant-current charging is performed until the capacity reaches 10mAh cm⁻¹. -2 Then at 20mA cm -2 A constant current discharge was applied until the voltage reached 0.4V. After 360 cycles under these conditions, the microstructure of the electrode deposition was characterized, and the results are as follows: Figure 2 As shown. Figure 2(a) and (b) show the microstructure of the electrodes of the battery without acetourea after cycling. As can be seen from the figures, a large amount of unevenly aggregated manganese dioxide deposits are attached to the carbon fiber surface, appearing as coarse, loose granular or flaky aggregates. These undissolved manganese dioxide deposits gradually accumulate during cycling, not only hindering the effective utilization of active materials and leading to a decrease in battery coulombic efficiency, but also potentially detaching from the electrode surface and clogging the positive electrode channel of the flow battery, affecting the long-term stable operation of the system. In stark contrast, from... Figure 2 As observed in (c) and (d), the electrode surface morphology obtained in the electrolyte system with added acetourea is significantly improved. The carbon fiber surface is clean after cycling, with no obvious manganese dioxide residue or aggregation observed, indicating that the deposited manganese dioxide can achieve highly reversible dissolution during discharge. These morphological differences directly demonstrate that the introduction of acetourea effectively optimizes the deposition / dissolution process of manganese dioxide, significantly improving its electrochemical reversibility, thereby contributing to improved battery cycle stability and battery efficiency.

[0045] This invention reveals an innovative mechanism of action of acetourea as a functional additive in neutral zinc-manganese flow batteries. The core of this mechanism lies in constructing a reversible dynamic coordination mechanism to systematically optimize the deposition-dissolution behavior and electronic structure of MnO2 at the molecular scale. Specifically, during charging, acetourea molecules form coordination intermediates with Mn²⁺ through their functional groups, jointly participating in the electrochemical deposition reaction on the electrode surface. The coordination of acetourea avoids the intermediate byproduct Mn²⁺. 3+ The formation of Mn ²⁺ A uniform MnO2 layer is directly formed on the electrode in one step. This mechanism effectively guides the deposition of MnO2 in a more loose and stable manner, greatly improving the thoroughness and reversibility of its stripping reaction. In summary, acetourea, by constructing a dynamically reversible coordination system, systematically optimizes the deposition morphology, crystal structure, and charge transport behavior of MnO2 at the molecular level, thereby synergistically improving the cycle stability and rate performance of zinc-manganese redox flow batteries.

[0046] 2. At 20 mA cm -2 At current density, 10 mAh cm -2 Performance tests were conducted on the flow battery at a fixed areal capacity, and the results are shown in [Figure number missing]. Figure 3 Blank CE is the positive electrolyte from Comparative Example 1, and Ace CE is the positive electrolyte from Example 1.

[0047] according to Figure 3The cycle performance test results shown demonstrate that acetourea additive plays a crucial role in enhancing the overall electrochemical performance of zinc-manganese flow batteries. Specifically, the battery without acetourea exhibits significant performance degradation after fewer than 80 cycles, corresponding to the downward trend of the short triangle in the graph, indicating poor electrochemical reversibility and insufficient cycle stability. However, after introducing an appropriate amount of acetourea, the battery's coulombic efficiency remained above 95% throughout the entire test, as shown by the red (EE) and green (CE) lines in the graph, exhibiting excellent cycle retention and reaction reversibility. These results clearly demonstrate that the addition of acetourea effectively enhances the structural reversibility of the manganese-based cathode material during the deposition-dissolution process, suppresses irreversible loss of active materials and the occurrence of side reactions, thereby significantly improving the overall cycle life and operational stability of the battery.

[0048] 3. At 10-60 mA cm -2 Different current densities, charging to 10 mAh cm -2 The rate performance test results of zinc-manganese neutral flow batteries with and without acetourea under the specified conditions are shown in the figure. Figure 4 and Figure 5 .in, Figure 4 The graph shows the average coulombic efficiency and average energy efficiency after 10 cycles at different current densities. Figure 5 This is a graph showing the voltage-time results.

[0049] right Figure 4 and Figure 5 Comprehensive analysis shows that the acetourea additive plays a crucial role in improving the electrochemical performance of this system. From... Figure 4 The left side of the chart shows coulombic efficiency, and the right side shows energy efficiency data. It can be seen that the battery with added acetourea exhibits a significant advantage during cycling. The battery without acetourea has a relatively low coulombic efficiency, mainly due to the non-uniformity of manganese dioxide during the deposition-dissolution process, which easily leads to localized blockage of the electrode surface and a decrease in mass transfer efficiency, resulting in energy loss and maintaining a low overall energy efficiency. In contrast, the battery with added acetourea effectively solves the above problems, achieving an energy efficiency of up to 80%. Coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) focus on the ratio of energy storage and release processes in the energy storage device.

[0050] (1) (2) (3) Among them, C discharge This indicates the battery's discharge capacity during cycling, while C... charge This indicates the charging capacity. Additionally, V... dischargeThis indicates the battery's discharge voltage, V. charge This indicates the charging voltage.

[0051] This fully demonstrates the positive effect of the additive on improving battery cycle stability and electrochemical reaction reversibility.

[0052] from Figure 5 Further observation of the charge-discharge voltage curves reveals that the introduction of acetourea significantly enhances the voltage stability of the battery operation. In the battery system with added acetourea, the voltage plateau remains stable even under high current density charge-discharge, without significant fluctuations. In contrast, the voltage curve of the system without added acetourea exhibits larger polarization fluctuations and plateau tilt. This result directly confirms the stabilizing effect of acetourea on the electrolyte system, helping to suppress side reactions and ensure stable battery operation at high rates. In summary, the introduction of acetourea, by optimizing the deposition behavior of manganese dioxide, improving mass transfer at the electrode interface, and stabilizing the operating voltage, collectively contributes to the synergistic improvement of the cycle performance and rate performance of zinc-manganese redox flow batteries.

[0053] At room temperature, tests were conducted using a LabRAM HR Evolution confocal Raman microspectroscopy system equipped with a 633 nm excitation source, and the collected data were obtained. Figure 6 The Raman spectra shown are as follows. (In the figure, Blank is the electrolyte of Comparative Example 1, and Ace is the electrolyte of Example 1.) After the addition of acetourea, the proportion of strong hydrogen bonds in the solution increased from 27.42% to 30.41%, while the proportion of weak hydrogen bonds decreased from 70.67% to 67.48%.

[0054] Here, we define strong and weak hydrogen bonds based on Raman spectral characteristics: a strong hydrogen bond is defined as an OH stretching vibration peak located at 3000-3200 cm⁻¹. -1 Strong hydrogen bonds have high binding energies, reflecting a tight interaction network between water molecules and acetourea molecules; weak hydrogen bonds are characterized by OH stretching vibration peaks located at 3400-3600 cm⁻¹. -1 Hydrogen bonds are of a limited range and have low binding energies, primarily characterizing the weak interactions between water molecules themselves or with ions.

[0055] The increased proportion of strong hydrogen bonds indicates that acetourea enhances intermolecular interactions, which directly optimizes the electrolyte microstructure and thus improves ion migration efficiency. This hydrogen bond network reconstruction, along with the optimization of deposition morphology and improved cycling performance, mutually reinforces the mechanism by which acetourea achieves performance enhancement through interfacial micro-regulation.

[0056] The experimental data above fully verify the significant advantages of the proposed positive electrode electrolyte in neutral zinc-manganese flow batteries. Specifically, acetourea molecules, through their unique coordination effect, effectively activate the reaction kinetics of the Mn²⁺ / MnO₂ couple: on the one hand, acetourea can form dynamic coordination bonds with Mn²⁺, significantly reducing the charge transfer energy barrier of Mn²⁺ oxidation and MnO₂ reduction, thereby accelerating the electrochemical reaction process. More importantly, the microstructure of this deposition layer exhibits porous and loose characteristics due to the coordination intermediate structure of acetourea, effectively avoiding the "dead manganese" accumulation problem caused by traditional dense MnO₂ layers. During discharge, the loose structure is more conducive to electrolyte penetration and ion diffusion, significantly reducing the loss of active materials.

[0057] The electrolyte system of this invention successfully achieves a synergistic improvement in high-rate performance and cycle stability: after 360 cycles, the coulombic efficiency still reaches 98.3%, which fully demonstrates its practical value in long-term energy storage scenarios.

[0058] Using the same method, cyclic tests were further conducted on other embodiments under test conditions of a current density of 20 mAcm⁻². -2 Under a window voltage of 1.98V and a temperature of 25℃±1℃, record the number of cycles when the coulombic efficiency is at its lowest of 95%, and the number of cycles at 10 mA cm⁻¹. -2 and 60 mA cm -2 Current density, charging to 10 mAh cm⁻¹ -2 The average energy density and average coulombic efficiency after 10 cycles are shown in Table 1.

[0059] Table 1

[0060] The contents not described in detail in this specification are existing technologies known to those skilled in the art, and will not be elaborated upon here.

[0061] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. Application of acetourea in neutral zinc-manganese flow batteries.

2. The application according to claim 1, wherein, The acetourea is used as an additive in the positive electrode electrolyte of a neutral zinc-manganese flow battery.

3. A positive electrode electrolyte for a neutral zinc-manganese flow battery, characterized in that, The positive electrode electrolyte includes a solvent, a solute, and an additive, wherein the additive is acetylurea.

4. The positive electrode electrolyte according to claim 3, wherein, Based on the total amount of the positive electrode electrolyte, the concentration of acetylurea is 0.05-0.1 mol / L.

5. The positive electrode electrolyte according to claim 3 or 4, wherein, The solute includes a manganese salt and a supporting electrolyte, wherein the supporting electrolyte includes potassium ions and / or sodium ions.

6. The positive electrode electrolyte according to claim 5, wherein, The potassium ions are derived from one or more of potassium sulfate, potassium chloride, and potassium nitrate.

7. The positive electrode electrolyte according to claim 5, wherein, Based on the total amount of the positive electrode electrolyte, the concentration of the supporting electrolyte is 0.5-3.0 mol / L.

8. The positive electrode electrolyte according to claim 5, wherein, Based on the total amount of the positive electrode electrolyte, the concentration of the manganese salt is 0.2-0.5 mol / L.

9. The positive electrode electrolyte according to claim 3 or 8, wherein, The manganese salt is selected from one or more of manganese sulfate, manganese chloride, and manganese acetate.

10. A neutral zinc-manganese flow battery, characterized in that, Includes the positive electrode electrolyte as described in any one of claims 3-9.

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