Sodium ion soft package battery with reference electrode and preparation method of sodium ion soft package battery

Abstract

The invention relates to a sodion soft package battery with a reference electrode and a preparation method thereof, and the preparation method comprises the following steps: S1, carrying out lamination on a positive plate, a diaphragm and a negative plate according to a Z-shaped sequence, carrying out hot pressing shaping, and drying to obtain a core package; hot-pressing a sodium layer on the surface of the aluminum base material, and carrying out insulation treatment on an aluminum base material area which is not covered with the sodium layer to obtain a reference electrode; the thickness of the sodium layer is 0.1 mm to 0.3 mm; the area of the sodium layer in the reference electrode is 10%-25% of the area of the core package; and S2, attaching the sodium layer of the reference electrode to the core package for aluminum-plastic film packaging, injecting an electrolyte, sealing, infiltrating, and pre-activating to obtain the sodium ion soft package battery with the reference electrode. According to the preparation method disclosed by the invention, after the reference electrode containing the sodium layer, which is obtained by adopting a hot pressing method, is arranged in the soft package battery, the oxide on the surface of the sodium layer is eliminated by using low-current discharge, so that the potential of the reference electrode is constant, and the monitoring accuracy and durability of the reference electrode are improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and particularly relates to a sodium-ion soft-pack battery with a reference electrode and its preparation method. Background Technology

[0002] With the rise of sodium-ion batteries, more and more research is being invested in optimizing and verifying various parameters of their materials and processes. In order to accurately and effectively characterize the specific effects of these improvements, higher requirements are being placed on sodium-ion battery testing methods.

[0003] A reference electrode is an auxiliary testing tool placed inside a battery that can independently monitor the potential changes of the positive and negative electrodes. By using a reference electrode in conjunction with impedance or other testing methods to monitor the changes in the independent potential and impedance of the positive and negative electrodes during the charging and discharging process of a pouch battery, the influence of material or process changes can be revealed, providing important information for analyzing the main materials of the positive and negative electrodes, electrode surfaces, electrolytes, and cell design.

[0004] Raccichini R et al. provided a comprehensive overview of various forms of operating errors in lithium-ion battery reference electrodes (Raccichini R, Amores M, Hinds G. Critical review of the use of reference electrodes in Li-ion batteries: a diagnostic perspective[J]. Batteries, 2019, 5(1): 12.). The geometry of the reference electrode, such as filament or foil, and its location, such as between separators or tabs, inevitably affect the current density during charge and discharge, leading to increased and unavoidable errors in potential and impedance measurements. Therefore, as a monitoring end, the design of the reference electrode needs to be optimized as much as possible to maintain a constant potential, minimize its impact on the battery's performance after being introduced into the battery, and provide a stable potential as a reference for measuring the positive and negative electrode potentials. This potential should not fluctuate significantly due to battery charge and discharge cycles, thus increasing measurement reliability and repeatability. These discussions also apply to the design of reference electrodes in sodium-ion batteries. Sodium metal is a common electrode material for coin cell half-cells and is also an ideal material for reference electrodes. There are two main structural forms in which sodium metal is introduced into the battery as a reference electrode: First, a layer of sodium is plated on the surface of metal wires or meshes such as platinum or aluminum using physical or chemical methods. This is complicated in practice, and the actual amount of sodium in the sodium plating layer is small, resulting in a loose structure and poor durability. This causes the reference electrode's own potential to be unable to remain stable for a long time, thus losing its monitoring function. Second, sodium metal sheets or strips are used as the reference electrode structure in sodium-ion pouch batteries. However, there are few reports of successful introduction of this substructure while ensuring its own potential stability and without causing performance loss to the battery itself.

[0005] Chinese invention patent CN117913402A discloses a device for detecting sodium deposition performance of hard carbon negative electrodes in sodium-ion batteries and its application. The device involves wrapping a sodium strip around the end of an aluminum electrode tab, insulating the tab, and then forming a reference electrode. This electrode is then inserted into a battery core for electrolyte injection, heat sealing, and formation. However, without heat sealing, the distance between the positive and negative electrodes and the separator increases significantly, inevitably increasing the contact resistance between the positive, negative, and reference electrodes. Furthermore, the dead zone caused by the insertion of the sodium strip into the electrode sheet, hindering sodium ion transport, affects battery performance and the accuracy of the reference potential. In addition, the sodium metal in the sodium strip is coated onto a metal substrate; if the substrate is not removed before directly wrapping the aluminum electrode tab, the accuracy of the reference potential will be further reduced.

[0006] Chinese invention patent CN117810578A discloses a sodium-ion battery reference electrode and its preparation method, as well as a three-electrode battery. It uses a metal wire as the reference electrode substrate, encapsulating the substrate with sodium metal and then rolling it into a sheet. However, the metal wire has a high internal resistance and a limited contact area with the sodium metal, leading to increased contact resistance of the reference electrode and affecting impedance and other performance tests.

[0007] Based on this, the present invention is proposed. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a sodium-ion pouch battery with a reference electrode and its preparation method. Sodium metal is hot-pressed onto an aluminum substrate with aluminum tabs to form a sodium layer of a certain thickness. Polyimide tape is used to insulate the areas of the aluminum substrate not covered by the sodium layer to obtain the reference electrode. Then, the sodium layer of the reference electrode is bonded to the core pack, encapsulated with an aluminum-plastic film, and vacuum-sealed. Finally, a low-current discharge process is used to remove oxides from the surface of the reference electrode to pre-activate it, thereby obtaining a sodium-ion pouch battery with a reference electrode.

[0009] The first objective of this invention is to provide a method for preparing a sodium-ion pouch cell with a reference electrode, comprising the following steps:

[0010] S1. The positive electrode, separator, and negative electrode are stacked in a Z-shaped order, hot-pressed and shaped, and then dried to obtain the core package;

[0011] A sodium layer is hot-pressed onto the surface of an aluminum substrate, and the area of ​​the aluminum substrate not covered by the sodium layer is insulated to obtain a reference electrode; the thickness of the sodium layer is 0.1mm-0.3mm; the area of ​​the sodium layer in the reference electrode is 10%-25% of the core package;

[0012] S2. The sodium layer of the reference electrode described in S1 is bonded to the core package described in S1 and encapsulated with an aluminum-plastic film. After injecting electrolyte, the package is sealed and pre-activated after wetting to obtain the sodium-ion soft-pack battery with the reference electrode.

[0013] In one embodiment of the present invention, in S1, the method for preparing the positive electrode and the negative electrode includes the following steps:

[0014] S11. Mix the positive and negative electrode active materials, conductive agent, binder and solvent evenly to obtain positive and negative electrode slurries respectively;

[0015] S12. The positive and negative electrode slurries are coated onto carbon-coated aluminum foil, and then dried and rolled to obtain positive and negative electrode sheets.

[0016] In one embodiment of the present invention, in S11, the positive electrode active material is selected from polyanionic compounds and / or layered oxides;

[0017] And / or, the negative electrode active material is titanium-based phosphate;

[0018] And / or, the conductive agent is selected from one or more of carbon nanotubes, acetylene black, conductive carbon black, conductive graphite, carbon fiber and graphene;

[0019] And / or, the adhesive is selected from one or more of polyolefins, fluorinated resins, polypropylene resins, and rubbers, for example, it may be one or more of polyvinylidene fluoride, styrene rubber, nitrile rubber, styrene-butadiene rubber (SBR), polyacrylamide (PAA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), butadiene rubber, modified butadiene rubber, carboxyl-modified styrene-butadiene rubber, and modified polyorganosiloxane polymers;

[0020] And / or, the solvent is selected from one or more of N-methyl-2-pyrrolidone, ethanol, and acetone;

[0021] And / or, the mass ratio of the positive and negative electrode active materials, conductive agent, binder and solvent is 90-95:2-8:1-5:130-170.

[0022] In one embodiment of the present invention, in S1, the temperature of the hot pressing is 40℃-80℃, the pressure is 0.5MPa-0.9MPa, and the time is 20s-60s.

[0023] In one embodiment of the present invention, in S1, the material for the insulation treatment is polyimide tape.

[0024] In one embodiment of the present invention, in S2, the electrolyte injection coefficient is 9g / Ah-12g / Ah.

[0025] In one embodiment of the present invention, in S2, the immersion temperature is 40°C-45°C and the time is 22h-26h.

[0026] In one embodiment of the present invention, in S2, the pre-activation is a constant current discharge of 10μA-100μA for 2h-4h, which eliminates oxides on the surface of the sodium layer by means of the discharge process.

[0027] In one embodiment of the present invention, in S2, the aluminum-plastic film needs to be perforated before use. The total depth of the perforation is increased by 0.15mm margin after the core package is hot-pressed, thereby ensuring that the core package containing the reference electrode and the aluminum-plastic film can fit tightly together.

[0028] In one embodiment of the present invention, the invention further includes the preparation of tabs, wherein a positive tab is welded to the positive electrode sheet of the core package, a negative tab is welded to the negative electrode sheet of the cell, and a reference tab is welded to a reference electrode.

[0029] In one embodiment of the present invention, the positive electrode tab, the negative electrode tab, and the reference electrode tab are exposed outside the aluminum-plastic film, the positive electrode tab and the negative electrode tab are led out in the same direction, and the reference electrode tab is led out in the opposite direction to the positive and negative electrode tabs.

[0030] A second objective of this invention is to provide a sodium-ion pouch cell with a reference electrode prepared by the method described above.

[0031] The technical solution of the present invention has the following advantages compared with the prior art:

[0032] (1) The preparation method described in this invention uses a hot pressing method to obtain a reference electrode containing a sodium layer. After the reference electrode is placed inside a soft-pack battery, a small current discharge is used to eliminate the oxide on the surface of the sodium layer, ensuring that the reference electrode potential is constant and improving the monitoring accuracy and durability of the reference electrode.

[0033] (2) The preparation method described in this invention uses an aluminum substrate as a sodium layer carrier. Sodium metal is rolled onto the aluminum substrate by a rolling method to form a reference electrode structure containing a sodium layer. This not only ensures that the sodium layer is firmly bonded to the aluminum substrate and increases the contact area, effectively reducing the contact internal resistance, but also reduces the thickness of the reference electrode. This will not cause the soft-pack battery to bulge out on a large surface, affecting the packaging and pressing the electrode surface, thus causing performance loss.

[0034] (3) The preparation method described in this invention places the reference electrode between the core package surface and the inner wall of the aluminum-plastic film, and leads the reference electrode tabs toward the opposite side of the positive and negative electrodes. This can reduce the interference of current changes on the reference potential and avoid the reference electrode shielding from hindering ion transport between the positive and negative electrodes, effectively reducing the fluctuation of the reference potential and the loss of cell performance.

[0035] (4) The reference electrode structure in the sodium-ion pouch cell with reference electrode described in this invention is widely applicable to sodium-ion pouch cells of polyanion, layered oxide, and other systems. By utilizing separately measured positive and negative electrode potentials or impedances, research can be conducted on sodium-ion battery structure design improvement, application scenario matching evaluation, and material mechanism studies. Attached Figure Description

[0036] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0037] Figure 1 This is a schematic diagram of the structure of the reference electrode of the present invention;

[0038] Figure 2 This is a schematic diagram of the structure of the sodium-ion soft-pack battery with a reference electrode according to the present invention.

[0039] Figure 3 This is the formation potential curve of a sodium-ion pouch cell with a reference electrode according to Example 1 of the present invention;

[0040] Figure 4 This is the formation potential curve of a sodium-ion pouch cell with a reference electrode, as shown in Comparative Example 1 of the present invention.

[0041] Figure 5 The 0.2C cycling potential curve of the sodium-ion pouch cell with a reference electrode in Example 1 of the present invention is shown.

[0042] Figure 6 The 0.2C cycling potential curve of the sodium-ion pouch cell with a reference electrode in Comparative Example 1 of this invention;

[0043] Figure 7 This is the 1C cycle potential curve of the sodium-ion pouch cell with a reference electrode in Embodiment 1 of the present invention;

[0044] Figure 8 This is the 1C cycle potential curve of the sodium-ion pouch cell with a reference electrode in Comparative Example 2 of the present invention.

[0045] Figure 9 This is the 1C cycling potential curve of the sodium-ion pouch cell with a reference electrode in Comparative Example 3 of the present invention. Detailed Implementation

[0046] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0047] In this invention, unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0048] In this invention, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0049] In this invention, unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0050] In this invention, unless otherwise stated, the diaphragm used in the embodiments of this invention is a polyethylene diaphragm with a thickness of 10 μm.

[0051] In this invention, unless otherwise stated, the concentration of the electrolyte used in the embodiments of this invention is 1 mol / L, and the electrolyte is prepared by dissolving sodium perchlorate in ethylene carbonate.

[0052] Example 1

[0053] Reference Figures 1-2 As shown, the sodium-ion pouch cell with a reference electrode and its preparation method in this embodiment specifically include the following steps:

[0054] S1, Core Packaging Preparation

[0055] S11. Preparation of positive and negative electrode slurries: Weigh 92.0g of positive and negative electrode active materials (sodium iron pyrophosphate for positive electrode and sodium titanium phosphate for negative electrode), 4.0g of conductive carbon black, 1g of conductive carbon nanotube powder, and 3.0g of polyvinylidene fluoride powder for binder, add 150g of N-methyl-2-pyrrolidone solvent, and place them in a ball mill jar and ball mill at 40rpm for 180min to obtain positive and negative electrode slurries respectively.

[0056] S12. Preparation of positive and negative electrode sheets: The positive and negative electrode slurries are poured into the material tank of the transfer coating machine. The transfer die head is controlled to coat both sides of the carbon-coated aluminum foil with a thickness of 14μm. After drying in an oven at 130℃, the sheets are rolled and die-cut using a roller press with a roller pressure of 4.0MPa to obtain positive electrode sheets with a size of 64mm*53mm and negative electrode sheets with a size of 69mm*55mm.

[0057] S13. Preparation of the core package: The positive electrode, separator, and negative electrode are stacked in a Z-shaped order, with 12 layers of positive electrode and 13 layers of negative electrode. The outermost layer and sides are covered with the separator and fixed with polypropylene tape. After hot pressing and shaping, the aluminum tabs are ultrasonically welded to the positive and negative tabs respectively. Then, it is placed in a vacuum oven with a vacuum degree of -0.095MPa and a temperature of 120℃ and baked for 12 hours. After that, it is transferred to a glove box and sealed in a self-sealing bag for storage.

[0058] S2. Preparation of aluminum-plastic film: The core thickness was measured to be 4.55mm using a micrometer. An additional 0.15mm was added to this thickness. The aluminum-plastic film was then punched with a punching machine to create dents. The punched aluminum-plastic film was then transferred to a glove box.

[0059] S3. Preparation of the reference electrode: Cut an aluminum foil with dimensions of 80mm × 58mm and a thickness of 0.016mm, and ultrasonically weld aluminum tabs to the middle of its short edge. Then, transfer it to a glove box and use PTFE tweezers to place 0.35g of sodium metal in the middle area of ​​the aluminum foil and gently press it to adhere the sodium metal to the aluminum foil. Place it in a self-sealing bag and squeeze out the air by hand to seal it. Then, place it on a hot-pressing metal plate, ensuring that the aluminum tabs at the aluminum foil weld points do not extend into the metal plate. Adjust the temperature of the hot press to 50℃ and the pressure to 0.6MPa, and hot press for 30s. After hot pressing, transfer the self-sealing bag to the glove box and tear off the contact area between the self-sealing bag and the sodium layer. Trim away the excess empty foil around the sodium layer and trim the excess of the polyimide tape so that the foil cutting edge is 1mm-2mm from the edge of the sodium layer. Use polyimide tape to stick the aluminum foil area not covered by the aluminum-sodium layer for insulation treatment. Then, trim the tape appropriately along the foil cutting edge, with the tape cutting edge 2mm-3mm from the foil cutting edge, to obtain a reference electrode with a sodium layer thickness of 0.2mm; wherein the area of ​​the sodium layer in the reference electrode is 20% of the core package;

[0060] S4. Preparation of a sodium-ion pouch cell with a reference electrode: The sodium layer of the reference electrode is aligned with the center of the large surface of the core pack. The lead-out direction of the reference tab is opposite to the lead-out direction of the positive and negative tabs. After being fixed with polyimide tape, it is placed in the perforation of the aluminum-plastic film. The aluminum-plastic film shell is then combined and sealed in a glove box using a heat-sealing machine. Each tab is then wrapped with polyimide tape for insulation. 11g of electrolyte is injected (injection coefficient is 9g / Ah-12g / Ah), and the opening is sealed under vacuum. Then, the voltage and internal resistance of the positive-negative, positive-reference, and negative-reference cells were measured using an AC internal resistance meter. After checking for internal short circuits and voltage abnormalities, the cells were immersed at 45°C for 24 hours. After immersion, the internal resistance and voltage were measured again. Then, the three-electrode pouch cell was loaded with a clamp and the clamping force was set to 380 kg. The reference electrode of the three-electrode pouch cell was connected to the positive terminal of the test cabinet, and the negative electrode was connected to the negative terminal of the test cabinet for pre-activation. The cells were discharged with a constant current of 20 μA for 3 hours to obtain a sodium-ion pouch cell with a reference electrode.

[0061] Comparative Example 1

[0062] The process is basically the same as in Example 1, except that pre-activation is not performed during the preparation of the sodium-ion pouch cell with a reference electrode. Specifically, the process includes the following steps:

[0063] Preparation of sodium-ion pouch battery with reference electrode: The sodium layer of the reference electrode is placed facing the center of the core pack, and the lead-out direction of the reference tab is opposite to the lead-out direction of the positive and negative tabs. After being fixed with polyimide tape, it is placed in the perforation of the aluminum-plastic film, the aluminum-plastic film shell is combined, and after being sealed in a glove box by a heat sealing machine, each tab is wrapped with polyimide tape for insulation treatment. 11g of electrolyte is injected (the electrolyte injection coefficient is 9g / Ah-12g / Ah), and vacuum sealing is performed. The voltage and internal resistance of positive-negative, positive-reference, and negative-reference are measured using an AC internal resistance meter. After checking for internal short circuits and voltage abnormalities, it is placed in 45℃ for 24h to obtain sodium-ion pouch battery with reference electrode.

[0064] Comparative Example 2

[0065] The process is basically the same as in Example 1, except that the area of ​​the sodium layer in the reference electrode is 5% of the core package by adjusting the size of the aluminum foil.

[0066] Comparative Example 3

[0067] The basic structure is the same as in Example 1, except that the area of ​​the sodium layer in the reference electrode is 30% of the core package by adjusting the size of the aluminum foil.

[0068] Comparative Example 4

[0069] Basically the same as Example 1, except that the thickness of the sodium layer in the reference electrode specifically includes the following steps:

[0070] Preparation of the reference electrode: Cut an aluminum foil with dimensions of 80mm × 58mm and a thickness of 0.016mm, and ultrasonically weld aluminum tabs to the middle of its short edge. Then, transfer it to a glove box and use PTFE tweezers to place 0.1g of sodium metal in the middle area of ​​the aluminum foil and press it gently to make the sodium metal stick to the aluminum foil. Place it in a self-sealing bag and squeeze it by hand to expel the air and seal it. Then place it on a hot-pressing metal plate, ensuring that the aluminum tabs at the aluminum foil weld points do not extend into the metal plate. Adjust the temperature of the hot press to 40℃ and the pressure to 0.5MPa and hot press for 20s. The remaining steps are the same as in Example 1, to obtain a reference electrode with a sodium layer thickness of 0.05mm. The area of ​​the sodium layer in the reference electrode is 20% of the core package.

[0071] Comparative Example 5

[0072] Basically the same as Example 1, except that the thickness of the sodium layer in the reference electrode specifically includes the following steps:

[0073] Preparation of the reference electrode: Cut an aluminum foil with dimensions of 80mm × 58mm and a thickness of 0.016mm, and ultrasonically weld aluminum tabs to the middle of its short edge. Then, transfer it to a glove box and use PTFE tweezers to place 0.7g of sodium metal in the middle area of ​​the aluminum foil and press it gently to make the sodium metal stick to the aluminum foil. Place it in a self-sealing bag and squeeze it by hand to expel the air and seal it. Then place it on a hot-pressing metal plate, ensuring that the aluminum tabs at the aluminum foil weld points do not extend into the metal plate. Adjust the temperature of the hot press to 80℃ and the pressure to 0.5MPa and hot press for 60s. The remaining steps are the same as in Example 1, to obtain a reference electrode with a sodium layer thickness of 0.4mm. The area of ​​the sodium layer in the reference electrode is 20% of the core package.

[0074] Test Example 1

[0075] The voltage and internal resistance of the positive electrode to the negative electrode, the positive electrode to the reference electrode, and the negative electrode to the reference electrode were measured using an AC internal resistance meter after injection and immersion. The results are shown in Table 1.

[0076] Table 1

[0077]

[0078] From Table 1 and Figures 3-4 It can be seen that the thickness and area ratio of the sodium layer have a significant impact on the accuracy and stability of the reference electrode. In Example 1, the monitored voltage and internal resistance were normal during the initial assembly and long-term testing. In Comparative Example 1, the difference was not significant in the initial assembly stage, but the long-term cycle performance was unstable in the later stage. In Comparative Example 2, after reducing the area ratio of the sodium layer, the contact internal resistance of the positive-reference and negative-reference electrodes increased significantly compared to the Example 1. In Comparative Example 3, the decrease in internal resistance was not significant. During hot pressing, due to the increased amount of sodium metal, the edges of the sodium layer after hot pressing curled up, failing to fully adhere to the aluminum foil, affecting the stability of the subsequent reference potential. In Comparative Example 4, due to the excessively thin sodium sheet in the reference electrode, the potential monitoring data and internal resistance monitoring data of the positive-reference and negative-reference electrodes were unstable and not applicable to practical use. In Comparative Example 5, due to the increased mass of the reference electrode, the internal resistance decreased to some extent. However, due to the excessive thickness, during the assembly of the soft-pack battery, the presence of the reference electrode prevented the aluminum-plastic film in other parts from tightly wrapping the cell, leading to abnormal battery cycling during long-term cycling.

[0079] Test Example 2

[0080] The sodium-ion pouch cells with reference electrodes in Examples 1 and Comparative Examples 1-5 were subjected to two constant current charge-discharge cycles at room temperature (0.1C) to activate the cells. Then, performance tests such as cycle (1C) and rate were performed. During the tests, a test cabinet was always used to monitor the independent potentials of the positive and negative electrodes by connecting the positive electrode to the reference electrode and the negative electrode to the reference electrode.

[0081] The formation potential curves of sodium-ion pouch cells with reference electrodes in Example 1 and Comparative Example 1 are as follows: Figures 3-4 As shown;

[0082] The 0.2C cycling potential curves of the sodium-ion pouch cells with reference electrodes in Example 1 and Comparative Example 1 are shown below. Figures 5-6 As shown;

[0083] The 1C cycling potential curves of sodium-ion pouch cells with reference electrodes in Examples 1 and Comparative Examples 2-3 are shown below. Figures 7-9 As shown;

[0084] Table 2 shows the stability test results of the reference electrode during long-term cycling.

[0085] Table 2

[0086]

[0087]

[0088] from Figures 3-9 As can be seen from Table 2, the thickness and area ratio of the sodium layer have a significant impact on the long-term stability of the reference electrode. The specific analysis is as follows:

[0089] Comparing Example 1 and Comparative Example 1, it can be seen that the formation monitoring results show that the sodium-ion pouch cell with reference electrode in Example 1 exhibits the same trend in the positive and negative electrode reference potential changes during the first charge-discharge process as the coin cell characterization trend of the main positive and negative electrode materials. The sodium titanium phosphate negative electrode maintains a plateau potential of 2.1V without abnormal fluctuations after sodium intercalation, confirming the accuracy of the reference electrode potential. The positive-reference and negative-reference potentials of the unactivated reference electrode in Comparative Example 1 are not significantly different from those in Example 1. However, the cycle monitoring results show that the sodium-ion pouch cell with reference electrode in Example 1 exhibits a normal trend in the positive and negative electrode reference potentials during 0.2C room temperature cycling, confirming the stability of the reference electrode potential. In contrast, the unactivated reference potential in Comparative Example 1 shows significant abnormal fluctuations, with the negative electrode reference potential showing an upward trend, indicating poor stability of the unactivated reference electrode potential.

[0090] Comparing Example 1 and Comparative Examples 2-3, it can be seen that the sodium-ion pouch cells with reference electrodes in Comparative Examples 2-3, where the sodium layer area ratio exceeds the characteristic range, exhibit abnormal potential fluctuations during 1C room temperature cycling. The negative electrode reference potential fluctuation of Comparative Example 2 exceeds 50mV, and although the negative electrode reference potential of Comparative Example 3 fluctuates by approximately 30mV, it shows an upward trend, indicating that an excessively large sodium layer area ratio affects the accuracy of the reference potential.

[0091] Comparing Example 1 and Comparative Examples 4-5, it can be seen that in Comparative Example 4, the sodium sheet in the reference electrode is too thin, resulting in a 200mV deviation in the potential monitoring data. The monitoring values ​​are unstable and cannot be used in practical applications. In Comparative Example 5, the reference electrode is too thick, resulting in a small fluctuation in the negative electrode potential. During the assembly of the soft-pack battery, the aluminum-plastic film in other parts cannot tightly wrap the cell, leading to abnormal battery cycling during long-term cycling.

[0092] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a sodium-ion pouch cell with a reference electrode, characterized in that, Includes the following steps: S1. The positive electrode, separator, and negative electrode are stacked in a Z-shaped order, hot-pressed and shaped, and then dried to obtain the core package; A sodium layer is hot-pressed onto the surface of an aluminum substrate, and the area of ​​the aluminum substrate not covered by the sodium layer is insulated to obtain a reference electrode; the thickness of the sodium layer is 0.1mm-0.3mm; the area of ​​the sodium layer in the reference electrode is 10%-25% of the core package; S2. The sodium layer of the reference electrode described in S1 is bonded to the core package described in S1 and encapsulated with an aluminum-plastic film. After injecting electrolyte, the package is sealed and pre-activated after wetting to obtain the sodium-ion soft-pack battery with the reference electrode.

2. The method for preparing a sodium-ion pouch cell with a reference electrode according to claim 1, characterized in that, In S1, the method for preparing the positive and negative electrode sheets includes the following steps: S11. Mix the positive and negative electrode active materials, conductive agent, binder and solvent evenly to obtain positive and negative electrode slurries respectively; S12. The positive and negative electrode slurries are coated onto carbon-coated aluminum foil, and then dried and rolled to obtain positive and negative electrode sheets.

3. The method for preparing a sodium-ion pouch cell with a reference electrode according to claim 1, characterized in that, In S1, the hot pressing temperature is 40℃-80℃, the pressure is 0.5MPa-0.9MPa, and the time is 20s-60s.

4. The method for preparing a sodium-ion pouch cell with a reference electrode according to claim 1, characterized in that, In S1, the insulating material is polyimide tape.

5. The method for preparing a sodium-ion pouch cell with a reference electrode according to claim 1, characterized in that, In S2, the electrolyte injection coefficient is 9 g / Ah-12 g / Ah.

6. The method for preparing a sodium-ion pouch cell with a reference electrode according to claim 1, characterized in that, In S2, the immersion temperature is 40℃-45℃ and the immersion time is 22h-26h.

7. The method for preparing a sodium-ion pouch cell with a reference electrode according to claim 1, characterized in that, In S2, the pre-activation is a constant current discharge of 10μA-100μA for 2-4 hours.

8. The method for preparing a sodium-ion pouch cell with a reference electrode according to claim 1, characterized in that, It also includes the preparation of tabs, welding the positive tab to the positive electrode sheet of the core package, welding the negative tab to the negative electrode sheet of the cell, and welding the reference tab to the reference electrode.

9. The method for preparing a sodium-ion pouch cell with a reference electrode according to claim 8, characterized in that, The positive electrode tab, negative electrode tab, and reference electrode tab are exposed on the aluminum-plastic film. The positive electrode tab and the negative electrode tab are led out in the same direction, and the reference electrode tab is led out in the opposite direction to the positive and negative electrode tabs.

10. A sodium-ion pouch cell having a reference electrode prepared by the method according to any one of claims 1-9.

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