A bipolar plate for zinc-based flow batteries and its preparation method

Abstract

This invention discloses a bipolar plate for zinc-based flow batteries and its preparation method, belonging to the field of battery electrode material preparation technology. This invention adds ferroelectric nanoparticles to the bipolar plate composition and controls the ratio. By applying a high-voltage corona discharge, it promotes the formation of uniform and switchable polarization within the ferroelectric phase of the bipolar plate to guide ordered zinc ion migration. This is significant for solving the dendrite problem generated during zinc electrodeposition in zinc-based flow batteries during cycling, providing a practical strategy for the stable operation of zinc-based flow batteries, and further offering opportunities for zinc-based flow batteries with controllable zinc electrodeposition for large-scale energy storage applications.

Description

Technical Field

[0001] This invention belongs to the field of battery electrode preparation technology, and relates to a bipolar plate for zinc-based flow batteries and its preparation method. Background Technology

[0002] Against the backdrop of the international push for low-carbon and clean energy development, renewable energy sources such as wind and solar power have seen continuous growth in recent years. However, the dependence of these renewable energy sources on weather, time, and geographical conditions leads to intermittent and unstable energy production, thus affecting their widespread application. Currently, using electrochemical energy storage devices is an effective way to improve grid stability and efficiency, and it has wide applications in portable electronic devices and backup power supplies, thus it can also be used to achieve stable renewable energy power generation. In large-scale energy storage, electrochemical energy storage offers greater flexibility and portability compared to pumped hydro storage and compressed air technologies. Furthermore, in electrochemical energy storage, aqueous redox flow batteries (RFBs) offer lower costs and higher safety compared to more mature lithium-ion and sodium-ion battery systems. Therefore, RFBs have great potential in realizing large-scale grid-scale energy storage.

[0003] Since the advent of the first flow battery, flow battery technology has developed for over fifty years, evolving into more than ten types of RFBs. Although vanadium redox flow batteries have the highest commercialization rate and more mature technology, zinc-bromine flow batteries (ZBFBs) stand out due to their low cost, high safety, high battery potential (1.85V), and high theoretical energy density (440Wh / kg). -1 This makes it one of the strongest competitors among RFBs. Currently, zinc-bromine flow batteries have achieved practical applications at the megawatt level and are in the demonstration application stage, with very promising commercial application prospects. ZBFBs consist of a positive electrode chamber and a negative electrode chamber separated by an ion-exchange membrane, and a storage tank connected to the positive and negative electrode chambers. The positive and negative electrode electrolytes containing the active material ZnBr2 are stored in the storage tank. Redox reactions (e.g., negative electrode: ZnBr2) are carried out by continuously pumping circulating electrolyte to the negative and positive electrodes. 2+ / Zn, positive electrode: Br - The zinc-bromine flow battery (ZBFBs) can convert electrical energy into chemical energy by adjusting the area and thickness of the membrane electrode assembly (MEA) to change its power. Therefore, the power and energy of the ZBFB can be independently designed by adjusting the assembly to achieve the optimal combination of capacity and power.

[0004] In summary, zinc-bromine flow batteries exhibit excellent application potential, but their practical commercial application is hindered by several issues, particularly the presence of zinc dendrites and "dead zinc" on the negative electrode side. During charging, zinc ions in the electrolyte migrate towards the negative electrode, electrodepositing metallic zinc on its surface. Discharging corresponds to the dissolution of zinc. However, even after discharge, residual zinc remains on the negative electrode surface, failing to participate in the electrochemical reaction. This leads to the deposition and accumulation of metallic zinc on the negative electrode during recharging, forming zinc dendrites. After multiple charge-discharge cycles, these dendrites grow and may even puncture the separator, causing a short circuit and battery failure. Furthermore, the weak bonding between the protruding zinc dendrites and the substrate can cause them to detach due to the impact of the flowing electrolyte, resulting in significant capacity loss and even damage to the cycle pump. Simultaneously, zinc electrochemically deposited during charging may remain on the separator, rarely participating in the electrochemical reactions during charge-discharge cycles, accumulating to form "dead zinc," leading to increased internal resistance and reduced energy efficiency.

[0005] Many solutions have been proposed to address the problems of zinc dendrite growth and dead zinc at the negative electrode, mainly including: adding electrolyte additives, controlling electrolyte flow rate and volume, and modifying the bipolar plate formulation. Among these, bipolar plate formulation modification is one of the most direct and effective approaches. On the one hand, modified bipolar plates can regulate the homogenization of the surface electric field and reduce the nucleation barrier for zinc ions; on the other hand, modified bipolar plates can induce the oriented deposition of zinc, thereby preventing the formation of zinc dendrites and dead zinc. This invention prepares a ferroelectric phase modified bipolar plate for zinc-based flow batteries. The preparation method is simple, low-cost, and easy to mass-produce. It pioneers a novel bipolar plate for zinc-based flow batteries, largely solving the problems of zinc dendrite growth and hydrogen evolution corrosion at the negative electrode, and providing valuable guidance for the design and development of commercially viable zinc-based flow batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a bipolar plate for zinc-based flow batteries and its preparation method in the field of battery electrode material preparation technology. This invention incorporates selected ferroelectric nanoparticles, such as lithium niobate, into the bipolar plate formulation through a mixing process. The mixture is then extruded into sheets and subjected to high-voltage corona polarization treatment. This induces uniform and switchable electrode polarization within the ferroelectric phase, forming a protective layer that guides orderly zinc ion migration. This addresses the problem of zinc dendrites growing and piercing the separator, leading to short-circuit failure. It also reduces the shedding of deposited zinc from the bipolar plate surface, preventing the formation of dead zinc and thus mitigating battery capacity decay caused by active material loss. Furthermore, it suppresses side reactions between the deposited zinc surface and the electrolyte. This invention, based on a modified formulation of ferroelectric phases such as lithium niobate, effectively suppresses zinc dendrite growth and hydrogen evolution corrosion side reactions in zinc-based flow batteries. It provides a practical strategy for the future development of stable zinc-based flow batteries and further opens up opportunities for zinc-based flow batteries with controllable zinc electrodeposition for large-scale energy storage applications.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] High-density polyethylene, conductive carbon black, conductive graphite, and ferroelectric nanoparticles are mixed. The resulting mixture is then subjected to intensive mixing, with an appropriate compatibilizer added during the mixing process to obtain a viscous slurry. This slurry is extruded, calendered into sheets, and cooled to obtain a bipolar plate filled with ferroelectric nanoparticles. The resulting bipolar plate is then placed in a corona polarization device, where a high-voltage corona discharge is applied to polarize the ferroelectric nanoparticles. The electric field direction points from the surface of the bipolar plate towards the distance. This high-voltage corona polarization induces uniform and switchable polarization to guide the orderly migration of zinc ions.

[0009] Specifically, a method for preparing a bipolar plate for a zinc-based flow battery includes the following steps:

[0010] (1) Ferroelectric nanoparticles are mixed with high-density polyethylene, conductive carbon black and conductive graphite in a certain proportion.

[0011] (2) The mixture obtained in step (1) is subjected to internal kneading and kneading. An appropriate amount of compatibilizer is added during the kneading process to obtain a thick slurry. Then, it is extruded and calendered into sheets by a single screw or twin screw and cooled to obtain a bipolar plate filled with ferroelectric nanoparticles.

[0012] (3) The bipolar plate obtained in step (2) is placed in a corona polarization device. A high-voltage corona is applied to induce polarization of the ferroelectric nanoparticles, resulting in a bipolar plate for zinc-based flow batteries. High-voltage corona polarization induces uniform and switchable polarization within the ferroelectric phase to guide ordered zinc ion migration. The uniformity of the ferroelectric phase plays a crucial role in the performance of the bipolar plate. Non-uniform ferroelectric phase polarization leads to uneven cell distribution on the bipolar plate surface during battery operation, increasing the likelihood of zinc dendrite growth. Switchable corona polarization facilitates the directional control of zinc ion migration.

[0013] In the above technical solution, further, the ferroelectric nanoparticles in step (1) are one or more ferroelectric nanoparticles such as lithium niobate, potassium dihydrogen phosphate, barium titanate, zinc ferrite, zinc iron titanate, and strontium ferrite.

[0014] Furthermore, in step (1), the particle size of the ferroelectric nanoparticles is between 10-50 nm. The selection of the particle size takes into account various factors such as performance, raw material cost, process loss, and overall cost. Excessively large particle sizes (greater than 50 nm) will increase processing time and energy loss in subsequent processes such as mixing and extrusion, while also reducing the uniformity and repeatability of the prepared bipolar plates, resulting in poor battery performance such as coulombic efficiency. Conversely, excessively small particle sizes (less than 10 nm) of ferroelectric nanoparticles have excessively high raw material costs, and the performance of the bipolar plates prepared using them is close to that prepared using ferroelectric nanoparticles with the optimal particle size (10-50 nm). Therefore, considering all factors, the optimal particle size is selected as 10-50 nm.

[0015] In step (1), the mass percentage of ferroelectric nanoparticles in the mixture is controlled to be 1%-5%, preferably 2%-4%. An excessively high mass percentage will not further improve performance and will increase raw material costs, while an excessively low mass percentage will not significantly improve the electrochemical performance of the bipolar plate. The mass percentage of high-density polyethylene is 35%-45%. The appropriate addition of high-density polyethylene ensures that the bipolar plate has good strength and a smooth and stable molding process. The mass percentage of conductive carbon black is 26%-36%, and the mass percentage of conductive graphite is 10%-30%. The addition of conductive carbon black and conductive graphite is to improve the conductivity of the bipolar plate. The control of the mass percentage comprehensively considers performance and raw material cost factors.

[0016] The compatibilizer added in step (2) is YY-501 (Lubtop), with a mass ratio of 0.5%-1.5%, which increases the dispersion ability of ferroelectric nanoparticles in the mixture;

[0017] The mixing temperature in step (2) is 180-220℃. At this temperature, the raw materials melt well and have good fluidity. The mixing time is 20-40 minutes.

[0018] In step (2), the thickness of the ferroelectric nanoparticles filled with bipolar plates extruded and calendered by the screw is 0.7-1 mm, preferably 0.8 mm. The preferred thickness provides good welding performance of the bipolar plates, which is beneficial for the expansion and assembly of the fuel cell stack.

[0019] The polarization electric field strength in step (3) is 1.5-3 kV mm. -1 The electric field direction is from the surface of the bipolar plate to the distance, and the polarization time is 1-3 hours. The polarization electric field strength is relatively important. If the polarization electric field strength is too low, it will not be possible to successfully induce uniform switchable polarization inside the ferroelectric phase in the bipolar plate. If the polarization electric field strength is too high, it may cause the bipolar plate to break down.

[0020] In the preparation of ferroelectric modified bipolar plates, this invention uses lithium niobate (LiNbO3) as an example. The LiNbO3 protective layer is treated with corona polarization to induce uniform and switchable polarization, guiding ordered zinc ion migration. Simultaneously, the Li metal nodes in the LiNbO3 structure make the electric field on the zinc surface more uniform, resulting in smaller fluctuations in the electric field on the negative electrode surface and a more uniform surface current density during charging and discharging, thus leading to more uniform zinc deposition / dissolution. Furthermore, lithium niobate has a higher affinity for Zn, lowering the Zn nucleation barrier. This not only increases the zinc deposition rate but also promotes uniform Zn deposition, reduces zinc dendrite growth, and improves the cycle stability of zinc-based flow batteries. Similar to lithium niobate, the other ferroelectric phase materials used in this invention operate on a similar mechanism. After corona polarization treatment, these ferroelectric phase molecules can oriented to form a uniform and ordered microstructure phase, generating a directional electrostatic field that induces ordered zinc ion migration and accelerates the uniform deposition of zinc metal.

[0021] The advantage of this method is that:

[0022] The preparation process is simple, quick, and low-cost, requiring no expensive material growth equipment. The ferroelectric modified bipolar plates prepared by this method are stable and can effectively solve the dendrite and side reaction problems of zinc electrodeposition in zinc-based flow batteries during cycling. This provides a practical strategy for the future development of stable zinc-based flow batteries and further provides important guidance for zinc-based flow batteries with controllable zinc electrodeposition for large-scale energy storage applications. Attached Figure Description

[0023] Figure 1 The XRD results are those of the nano-lithium niobate used in Example 1;

[0024] Figure 2 The coulombic efficiency of the half-cell assembled with the corona-polarized lithium niobate ferroelectric phase modified bipolar plate prepared in Example 1 was tested.

[0025] Figure 3The coulombic efficiency of the half-cell assembled with lithium niobate iron-electric phase modified bipolar plates without corona polarization treatment prepared in Example 1 was tested.

[0026] Figure 4 Coulombic efficiency of half-cells assembled with bipolar plates without lithium niobate ferroelectric phase modification;

[0027] Figure 5 The coulombic efficiency of the half-cell assembled with corona-polarized lithium niobate ferroelectric phase modified bipolar plates prepared using larger particle size lithium niobate in Example 3 was tested.

[0028] Figure 6 The zinc-plated surface morphology of the corona-polarized lithium niobate ferroelectric phase modified bipolar plate prepared in Example 1;

[0029] Figure 7 The zinc-plated surface morphology of the lithium niobate ferroelectric phase modified bipolar plate prepared in Example 1 without corona polarization treatment;

[0030] Figure 8 The morphology of the zinc-plated surface of the bipolar plate without lithium niobate ferroelectric phase modification. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Example 1:

[0033] (1) Take 200g of lithium niobate with a particle size in the range of 10-50nm and mix it with 4000g of high-density polyethylene, 3500g of carbon black and 2300g of graphite.

[0034] (2) Add the mixture from (1) into a mixer at a mixing temperature of 180°C. Mix for 10 minutes, then add 100g of compatibilizer YY-501 (Lubtop) and continue mixing for 20 minutes.

[0035] (3) Take the product from (2) and put it into a twin-screw extruder. Extrude it through a sheet forming die. Set the extruder temperature to 220℃, control the die temperature at 180℃, control the calender roller spacing to 0.8mm, and cool to obtain a ferroelectric phase nanoparticle filled bipolar plate with a thickness of 0.8mm.

[0036] (4) Place the bipolar plate filled with ferroelectric nanoparticles from (3) in a corona polarization device and set the polarization electric field strength to 2.2 kV mm.-1 The electric field direction is from the surface of the bipolar plate to the distance, and the polarization time is 2h. This results in a modified bipolar plate with a uniformly arranged and switchable polarization lithium niobate iron phase, which is used in zinc-based flow batteries.

[0037] Example 2:

[0038] The lithium niobate ferroelectric modified bipolar plate was prepared using the same steps as in Example 1, except that the polarization electric field strength in step (4) of Example 1 was 2.2 kV mm. -1 Replace with 2.8kV mm -1 All other conditions remain unchanged.

[0039] Example 3:

[0040] The lithium niobate ferroelectric phase modified bipolar plate was prepared using the same steps as in Example 1, except that the lithium niobate particle size range of 10-50 nm in step (1) of Example 1 was replaced with 50-100 nm, while other conditions remained unchanged.

[0041] XRD characterization and analysis

[0042] Figure 1 The XRD results of the nano-lithium niobate used in Example 1 show that the main crystal diffraction peaks are consistent with the LiNbO3 phase peak (PDF#20-0631) of the hexagonal crystal system and space group R3c(161).

[0043] Performance Testing of Lithium Niobate Ferroelectric Phase Modified Bipolar Plates for Zinc-Based Flow Batteries

[0044] Figure 2 The coulombic efficiency of the half-cell assembled with the corona-polarized lithium niobate iron-phase modified bipolar plate prepared in Example 1 was tested. Pure zinc foil was used as the electrode, and the electrolyte was 3M ZnBr2 + 1M KCl. The test current condition was 20 mA / cm². -2 The zinc plating capacity is 80mAh cm -2 The corona-polarized lithium niobate ferroelectric phase modified bipolar plate reached 1500 cycles without short circuit, and the average zinc plating coulombic efficiency was 99.83%. As a control, to verify the extent of performance improvement of the lithium niobate ferroelectric phase modified bipolar plate after corona polarization, we tested the performance of the lithium niobate ferroelectric phase modified bipolar plate prepared in Example 1 without corona polarization treatment (i.e., the product obtained in step (3) of Example 1) and the bipolar plate without lithium niobate ferroelectric phase modification. Figure 3 The zinc plating performance of the lithium niobate ferroelectric modified bipolar plate prepared in Example 1 without corona polarization treatment was tested under the following conditions: test current condition 20 mA / cm². -2 The zinc plating capacity is 80mAh cm -2The battery developed a short circuit after approximately 700 cycles. This was caused by the electrolyte corroding the zinc anode surface, which triggered the growth of zinc dendrites that pierced the separator and caused an internal short circuit in the battery. Figure 4 For the zinc plating performance test of bipolar plates without lithium niobate ferroelectric phase modification, the test current condition was 20 mA cm⁻¹. -2 The zinc plating capacity is 80mAh cm -2 The battery experienced permanent short-circuit failure after approximately 400 cycles. This was because the growth of zinc dendrites caused the separator to be pierced, leading to an internal short circuit. Simultaneously, we verified the effect of particle size on bipolar plate performance. Figure 5 The zinc plating performance of the corona-polarized lithium niobate ferroelectric phase modified bipolar plate prepared in Example 3 was tested under the same test conditions as other samples for comparison and optimization. It can be seen that the zinc plating performance is improved compared to the bipolar plate without lithium niobate ferroelectric phase modification, but not as good as the half-cell assembled from the corona-polarized lithium niobate ferroelectric phase modified bipolar plate prepared in Example 1. This is due to the decreased mixing dispersion caused by the increased particle size, resulting in a reduced uniformity of the electric field distribution on the bipolar plate surface.

[0045] We also observed the galvanization morphology on the surface of the bipolar plate. Figure 6 The zinc-plated surface morphology of the corona-polarized lithium niobate ferroelectric phase modified bipolar plate prepared in Example 1 is shown. Figure 7 The zinc-plated surface morphology of the lithium niobate ferroelectric phase modified bipolar plate prepared in Example 1 without corona polarization treatment. Figure 8 The image shows the morphology of the zinc-plated surface of the bipolar plate without lithium niobate ferroelectric phase modification. Comparison reveals that the zinc plating on the lithium niobate ferroelectric phase modified bipolar plate after corona polarization treatment is dense, with no obvious dendrite growth morphology. This indicates that the lithium niobate ferroelectric phase after surface corona polarization treatment effectively suppresses zinc dendrite growth and side reactions during cycling. This is because corona polarization treatment generates a uniform and switchable polarization within the ferroelectric phase LiNbO3, guiding ordered zinc ion migration. Simultaneously, the Li metal nodes in the LiNbO3 structure make the electric field on the zinc surface more uniform, resulting in smaller fluctuations in the electric field on the negative electrode surface during charging and discharging, a more uniform surface current density, and thus more uniform zinc deposition / dissolution. Furthermore, lithium niobate has a higher affinity for Zn, lowering the Zn nucleation barrier, which not only increases the zinc deposition rate but also promotes uniform Zn deposition, reduces zinc dendrite growth, and improves the cycle stability of the battery.

[0046] In summary, the bipolar plate for zinc-based flow batteries and its preparation method proposed in this invention effectively solve the problems of zinc dendrite growth and corrosion side reactions in the negative electrode, providing a practical strategy for developing stable and reliable zinc-based flow batteries, and further providing important guidance for zinc-based flow batteries with controllable zinc electrodeposition for large-scale energy storage applications.

Claims

1. A method for preparing a bipolar plate for a zinc-based flow battery, characterized in that, The method includes the following steps: (1) Ferroelectric nanoparticles are mixed with high-density polyethylene, conductive carbon black, and conductive graphite in a certain proportion; the ferroelectric nanoparticles are lithium niobate with a particle size of 10-50 nm; the mass ratio of ferroelectric nanoparticles in the resulting mixture is 1%-5%, the mass ratio of high-density polyethylene is 35%-45%, the mass ratio of conductive carbon black is 26%-36%, and the mass ratio of conductive graphite is 10%-30%; (2) The mixture obtained in step (1) is subjected to internal kneading and kneading. During the kneading process, an appropriate amount of compatibilizer is added to obtain a thick slurry. Then, it is extruded and calendered into sheets and cooled to obtain a bipolar plate filled with ferroelectric nanoparticles. (3) The bipolar plate obtained in step (2) is polarized by applying a high voltage corona to the ferroelectric phase nanoparticles to obtain a bipolar plate for zinc-based flow batteries. The high voltage corona causes uniform and switchable polarization to be formed in the ferroelectric phase of the bipolar plate to guide the orderly migration of zinc ions.

2. The method for preparing a bipolar plate according to claim 1, characterized in that, The compatibilizer added in step (2) is YY-501, with a mass ratio of 0.5%-1.5%.

3. The method for preparing a bipolar plate according to claim 1, characterized in that, The temperature for intensive mixing in step (2) is 180-220℃, and the mixing time is 20-40 minutes.

4. The method for preparing a bipolar plate according to claim 1, characterized in that, In step (2), the thickness of the bipolar plate filled with extruded and calendered ferroelectric nanoparticles is 0.7-1 mm.

5. The method for preparing a bipolar plate according to claim 1, characterized in that, The polarization electric field strength in step (3) is 1.5-3 kV mm. -1 The electric field direction is from the surface of the bipolar plate to the distance, and the polarization time is 1-3 hours.

6. A bipolar plate, characterized in that, It is prepared by the method described in any one of claims 1-5.

7. A zinc-based flow battery, characterized in that, It contains the bipolar plate as described in claim 6.

Images