A method for preparing a coated electrode and applications thereof

Abstract

The application discloses a preparation method and application of a battery coating electrode, which comprises the following steps: mixing ZSM-5 powder and MCM-41 powder, and uniformly coating the mixed powder on a zinc foil to obtain the coating electrode. 2+ The coating electrode has good electrochemical performance, such as high cycle stability, excellent surface corrosion resistance, good dendrite growth resistance, adjusted Zn

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a method for preparing a coated electrode and its application. Background Technology

[0002] Developed in the 1970s, lithium-ion batteries once dominated the electric vehicle and electronics markets. However, in recent years, the scarcity of lithium metal resources and their hidden safety hazards have limited their further application. Aqueous zinc-ion batteries, with their high specific capacity (820 mAh g⁻¹) and low redox potential (-0.762 V vs. SHE), are a powerful alternative to lithium-ion batteries. The electrolyte in zinc-ion batteries can be composed of water, acidic electrolytes, alkaline hydroxides, and soluble salts. Compared to traditional organic electrolytes, they offer superior safety, high ionic conductivity, and rapid ion diffusion kinetics, resulting in better battery performance. However, the hazards of dendrite growth, hydrogen evolution, and corrosion reactions inherent in aqueous electrolytes cannot be ignored. These problems can lead to the loss of active materials and, more seriously, short circuits. These issues are the fundamental reasons affecting the long-term development of zinc-ion batteries.

[0003] Dendrite growth and water-induced corrosion and passivation reactions are the main reasons limiting the cycle life of zinc-ion batteries. Firstly, free water and Zn in the electrolyte... 2+ The solvent water of ions will be in Zn 2+ When the zinc anode reaches the electrolyte, a competitive reaction occurs, which not only generates H2, increasing the internal pressure of the battery, but also produces basic zinc sulfate as a byproduct. Inhomogeneity on the zinc anode surface leads to dendrite growth, which in severe cases can puncture the separator, causing battery failure. Currently, a large amount of research is dedicated to improving the side reaction problems of zinc-ion battery anodes. The measures taken can be broadly categorized into constructing artificial electrode-electrolyte interfaces, electrolyte modification, and constructing 3D zinc anode structures. These methods can effectively improve the survival environment of zinc metal anodes in aqueous electrolytes and reduce water corrosion on the zinc anode surface. The construction of artificial interfaces is widely used due to its simple and convenient preparation method and its ability to effectively inhibit dendrite puncture of the separator. However, the use of artificial coatings is also limited by irreversible detachment from the anode surface and the reduction of Zn content. 2+ The limitation of ion transport rate is a problem that needs to be solved urgently for high-performance aqueous zinc-ion batteries. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the prior art by proposing a method for preparing a coated electrode and its application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing a coated electrode, the specific steps of which are as follows:

[0006] S1. Thoroughly mix ZSM-5 powder and MCM-41 powder to obtain a primary hierarchical porous molecular sieve powder with a volume ratio of 7:3;

[0007] S2. Add PVDF binder at a mass ratio of 1:9 to the original porous molecular sieve powder, mechanically grind the mixture for 20 min, then add NMP organic solvent dropwise, and stir thoroughly for 12 h to obtain the original coating slurry for later use;

[0008] S3. Use sandpaper to sand off the ZnO passivation layer on the zinc foil surface to expose the unoxidized Zn. After ultrasonic treatment in alcohol, dry the treated zinc foil for later use.

[0009] S4. The porous molecular sieve coating slurry prepared in step S2 is uniformly coated onto zinc foil to a thickness of 50 μm. The coated electrode is then placed in a vacuum oven and dried at 80°C for 12 hours to remove NMP solvent. The coated zinc foil is then cut into circular electrode sheets with a diameter of 12 mm and a thickness of 150 μL to obtain the coated electrode. The application of this coated electrode in zinc batteries aims to increase the cycle stability of zinc batteries, reduce electrode corrosion, and regulate Zn content. 2+ Deposition and stabilization of negative electrode resistance changes.

[0010] The beneficial effects of this invention are as follows: This invention prepares a hierarchical porous molecular sieve coating by using microporous ZSM-5 molecular sieve and mesoporous MCM-41 molecular sieve in a volume ratio of 7:3. The 0.56 nm diameter micropores of ZSM-5 confine the Zn... 2+ The transport of water molecules in the ionic solvent structure creates a locally high-concentration electrolyte within the molecular sieve channels, which helps suppress the corrosion of the zinc anode by water molecules. Furthermore, the 2.5nm diameter mesoporous channels of MCM-41 accelerate the in-coating Zn... 2+ The ion transport kinetics reduce concentration polarization on the coating and zinc anode surface, accelerating the consumption of Zn. 2+ The addition of this material helps to suppress uncontrolled dendrite growth. Compared to pure microporous molecular sieve coatings, the hierarchical porous molecular sieve coating prepared in this invention increases the growth-promoting effect of Zn. 2+ The important property of rapid transport is a crucial complement to single-pore molecular sieve coatings. Therefore, the corrosion current obtained from Tafel fitting of the LSV curve of Z7M3 is 0.43 mA cm⁻¹. -2 It is far lower than the 0.55 mA cm of pure zinc anode. -2 Z7M3@Zn||Z7M3@Zn symmetrical cells at 1mA cm -2 and 1mAh cm -2Under suitable conditions, a long cycle life exceeding 1600 hours was achieved. Molecular sieve coatings, due to their safety and stability, are promising candidates for zinc anode coating protection. The realization of hierarchical porous molecular sieve coatings provides an effective solution to the remaining problems of single molecular sieve coatings. Attached Figure Description

[0011] Figure 1 It is a bare zinc and coated negative electrode symmetrical cell at 1 mA cm -2 Rate, 1mAh cm -2 Cyclic performance graph under capacity.

[0012] Figure 2 This involves corrosion current testing of bare zinc and Z7M3@Zn anodes in a three-electrode system.

[0013] Figure 3 Yes. CA curves of bare zinc and Z7M3@Zn coated anode symmetric cells.

[0014] Figure 4 These are the CV curves for bare zinc and Z7M3@Zn coated anodes.

[0015] Figure 5 The EIS curves of bare zinc and Z7M3@Zn coated negative electrodes are shown, along with the corresponding fitting circuits. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments should not be construed as limiting the present invention.

[0017] This embodiment provides a method for preparing a coated electrode. The specific steps of the method are as follows: S1. ZSM-5 powder and MCM-41 powder are thoroughly mixed to obtain a raw hierarchical porous molecular sieve powder with a volume ratio of 7:3;

[0018] S2. Add PVDF binder with a mass ratio of 1:9 to the original porous molecular sieve powder, mechanically grind the mixture for 20 min, add NMP organic solvent dropwise, and stir thoroughly for 12 h to obtain the original coating slurry for later use.

[0019] S3. Use sandpaper to grind off the ZnO passivation layer on the zinc foil surface to expose the unoxidized Zn. After ultrasonic treatment in alcohol, dry the treated zinc foil for later use.

[0020] S4. The porous molecular sieve coating slurry prepared in step S2 is uniformly coated onto zinc foil, with a coating thickness of 50 μm. The coated electrode is placed in a vacuum oven and dried at 80°C for 12 h to remove NMP solvent. The coated zinc foil is then cut into circular electrode sheets with a diameter of 12 mm and a thickness of 150 μm to obtain the coated electrode. The application of the coated electrode in zinc batteries increases the cycle stability of zinc batteries, reduces electrode corrosion, and stabilizes changes in negative electrode resistance.

[0021] The cycling performance of the coated electrode prepared in this embodiment is as follows: Figure 1 As shown, a bare zinc and a Zn||Zn symmetric cell with a coated anode is demonstrated at 1 mA cm⁻¹. -2 Current density and 1mAh cm -2 Long-cycle charge-discharge curves at areal capacity show that the bare zinc symmetric cell experiences a sudden and drastic voltage fluctuation after approximately 300 hours of cycling, followed by a sharp drop in polarization voltage after approximately 330 hours, indicating a short circuit caused by excessive dendrite growth within the cell. In contrast, the cell protected by the porous molecular sieve coating maintains stable cycling even after 1600 hours. During the initial cycling, the Z7M3@Zn cell maintains a lower polarization voltage (approximately 35 mV), lower than the Zn cell's polarization voltage (50 mV), indicating that while the coating inhibits corrosion, it also accelerates the growth of Zn on the negative electrode surface. 2+ The rapid transport of Zn is mainly attributed to the coating, which is closely attached to the negative electrode and has a large number of large-diameter MCM channels and electronegative sites, which can guide the Zn in the diffusion layer. 2+ Rapid migration to the negative electrode, while the numerous porous channels of the molecular sieve confine Zn 2+ The transverse transport of Zn on the electrode surface enables Zn 2+ It can be uniformly deposited on the surface of the zinc anode, ultimately enabling the battery to maintain stable cycling within 1600 hours.

[0022] The corrosion resistance test of the coated electrode prepared in this embodiment is as follows: Figure 2 As shown, the LSV of a three-electrode system was tested using platinum as the positive electrode and AgCl as the reference electrode. The corrosion resistance of bare zinc and Z7M3 coating-protected negative electrodes was evaluated. Figure 2 As shown, the corrosion current and corrosion potential were fitted using the TafelExtrapolation plugin in Origin software. For bare zinc anodes, the fitting results show a relatively large corrosion current (0.55 mA cm⁻¹). -2 The corrosion potential is also more negative (-1.0056 mV), which contrasts sharply with the corrosion current of 0.43 mA cm⁻¹ of the coated Z7M3@Zn anode. -2 The corrosion rate is much smaller than that of a bare zinc anode. This indicates that the coating significantly reduces the corrosion rate of the zinc anode. In the coated anode, the nanoscale pore structure of the molecular sieve confines the Zn...2+ The transport of water molecules in the solvent structure, and simultaneously, the numerous electronegative sites on the molecular sieve pore walls accelerate the transport of Zn. 2+ The transmission weakened Zn 2+ and O W The interaction between them makes Zn 2+ The desolvation process is easier when Zn reaches the negative electrode surface. 2+ The stepwise desolvation of the hierarchical porous molecular sieve significantly inhibits corrosion on the zinc anode surface. Furthermore, Figure 2 The potential for the hydrogen evolution reaction shown on the right decreases from -10.2 mV for bare zinc to -11.5 mV for Z7M3@Zn, further illustrating that the addition of porous molecular sieves makes the corrosion reaction on the negative electrode surface more difficult to occur.

[0023] The dendrite growth resistance test of the coated electrode prepared in this embodiment is as follows: Figure 3 As shown, the CA method was used to test the change of current density over time for different electrodes under constant potential conditions. The change in current density indicates the change in the active surface area of ​​the negative electrode during charging, which largely explains the change in dendrite growth of the negative electrode over time. Figure 3 As shown, the current density of the bare zinc anode increases uncontrollably during the first 600 seconds of charging, indicating that Zn 2+ During this process, continuous two-dimensional diffusion is maintained, according to the principle of minimum surface energy, Zn 2+ Zn is more easily deposited on the less curved parts of the anode surface protrusions, where there is a higher distorted electric field, thus gradually generating vertical Zn. 2+ The deposition morphology shows that the continuous growth of dendrites leads to a continuous increase in the electrode surface area, resulting in a continuous increase in current density. Worse still, the continuous growth of dendrites causes the dendrite tips to be positioned higher and higher (with the negative electrode surface as a reference), making it easier for the dendrites to absorb Zn from the diffusion layer. 2+ Deposited at the dendrite tips. Conversely, the anode protected by the Z7M3 coating rapidly enters stable three-dimensional diffusion after a brief two-dimensional diffusion. As shown in the figure, the CA curve of Z7M3@Zn shows that the current density rapidly stabilizes at 22 mA cm⁻¹ after approximately 100 s. -2 The stability of the current density implies that the active surface area of ​​the electrode also tends to stabilize with increasing time. 2+ During the vertical deposition process, orderly horizontal deposition also occurs. Due to the steric hindrance effect of the molecular sieve channels, numerous vertical nanopores in the Z7M3 coating exist within the Zn... 2+ Zn is restricted when migrating to the negative electrode. 2+ The horizontal transport of Zn enables a relatively uniform concentration field on the negative electrode surface. Therefore, it can uniformly distribute Zn. 2+ Flux, making Zn 2+ Uniform deposition results in a relatively smooth negative electrode surface.

[0024] The coated electrode prepared in this embodiment has adjustable Zn content. 2+ The deposition behavior was further revealed by the CV method, which showed that hierarchical porous molecular sieves regulate Zn deposition. 2+ Characteristics of sedimentation behavior. For example... Figure 4 As shown, the reduction peak of the CV curve ends at approximately 0 mA cm⁻¹. -2 The potential at the inflection point is the nucleation overpotential, at which point Zn 2+ Initially, it is reduced to Zn at the negative electrode. The magnitude of the nucleation overpotential indicates the ease of nucleation. The nucleation overpotential of Z7M3@Zn is significantly lower than that of the bare zinc negative electrode, |BB'|=29mV, indicating that the addition of a hierarchical porous molecular sieve coating is more conducive to Zn formation. 2+ Rapid deposition. In contrast, bare zinc anodes have a large nucleation overpotential, which is unfavorable for Zn deposition. 2+ Ion transport kinetics. Furthermore, the redox peak areas of the Z7M3 coated anode are much larger than those of the bare zinc anode, indicating that more reactive substances participate in the redox reaction on the electrode surface during the negative electrode process. 2+ The transmission dynamics are faster.

[0025] This application tested the in-situ EIS spectra of bare zinc anode and anode with Z7M3 coating, see [link to EIS analysis]. Figure 5 In the figure, the EIS spectrum is a semicircle in the high-frequency region and a straight line in the low-frequency region. Zview software was used to select a suitable circuit to fit the original EIS data, where R... s The ohmic impedance of the electrode and electrolyte can be approximated by the intercept of the initial high-frequency EIS curve with the real axis, R. ct The charge transfer resistance is shown in Table 1-1. The fitting results show that the bare zinc anode, after 50 cycles (1 mA cm⁻¹), exhibits the following resistance: -2 After R s and R ct The significant increase in R values ​​indicates that a large amount of basic zinc sulfate may have been generated on the electrode surface. The large amount of ion and electron-insulating byproducts hindered rapid ion transport and uniform deposition. Conversely, the coated electrode showed a decrease in R values ​​after 50 cycles. s and R ct The growth was only slight, possibly due to the small amount of basic zinc sulfate byproducts growing on the electrode surface, and the reduced desolvation effect of the hierarchical porous molecular sieve on Zn. 2+ The difficulty of deposition on the zinc anode surface, and therefore the ohmic impedance R s and charge transfer resistance R ct There were no significant fluctuations.

[0026] Table 1-1 EIS fitting results of bare zinc and Z7M3 coated electrodes before and after cycling.

[0027]

[0028] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a coated electrode, characterized in that: The specific steps of the method are as follows: S1. Thoroughly mix ZSM-5 powder and MCM-41 powder to obtain a primary hierarchical porous molecular sieve powder with a volume ratio of 7:3; S2. Add PVDF binder at a mass ratio of 1:9 to the original porous molecular sieve powder, mechanically grind the mixture for 20 min, then add NMP organic solvent dropwise, and stir thoroughly for 12 h to obtain the original coating slurry for later use; S3. Use sandpaper to sand off the ZnO passivation layer on the zinc foil surface to expose the unoxidized Zn. After ultrasonic treatment in alcohol, dry the treated zinc foil for later use. S4. The porous molecular sieve coating slurry prepared in step S2 is uniformly coated onto zinc foil with a coating thickness of 50 μm. The coated electrode is placed in a vacuum oven and dried at 80°C for 12 h to remove NMP solvent. The coated zinc foil is then cut into circular electrode sheets with a diameter of 12 mm and a thickness of 150 μm to obtain the coated electrode.

2. The application of a coated electrode prepared by the method described in claim 1 in a zinc battery, to increase the cycle stability of the zinc battery, reduce electrode corrosion, and regulate Zn content. 2+ Deposition and stabilization of negative electrode resistance changes.

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