Preparation method of composite aluminum foil, composite pole piece and negative-electrode-free sodium ion battery

Abstract

The invention discloses a preparation method of a composite aluminum foil, a composite pole piece and a negative-electrode-free sodium ion battery. The composite aluminum foil comprises a substrate and positive and negative electrode areas alternately arranged on two sides of the substrate, aluminum foil layers are arranged in the positive and negative electrode areas, and the positive and negative electrode areas on two sides of the substrate correspond to each other. The composite pole piece disclosed by the invention can be folded in a Z shape and assembled into a pole group or a battery cell to be packaged, so that the negative-electrode-free sodium ion battery is prepared, the production efficiency of an assembling section of the pole group or the battery cell is effectively improved, and the situation that the production rhythm is disrupted due to abnormal conditions such as damage of an aluminum foil in the lamination and winding process is avoided; and the consistency of the production process can be improved by controlling the processing process, and the potential safety hazard of using the battery by the terminal is greatly reduced. The glued diaphragms are arranged on the two sides of the aluminum foil of the composite pole piece to serve as protective layers, so that the metal surface with high surface activity is effectively prevented from being polluted, and certain mechanical strength can be provided for the aluminum foil.

Description

Technical Field

[0001] This invention relates to a method for preparing composite aluminum foil, composite electrode, and a negative electrode-free sodium-ion battery. Background Technology

[0002] Sodium-ion batteries are batteries that use one or more of the following materials as the positive electrode: layered oxides (mainly nickel-iron-manganese oxides and copper-iron-manganese oxides), Prussian blue analogues (such as iron-based Prussian white), and polyanions (such as sulfates and phosphates), and carbon materials (such as hard carbon and soft carbon) as the negative electrode. They primarily use esters and ethers as solvents, with sodium added as the negative electrode. + The electrolyte is formed by combining metal salts (such as sodium fluoride, sodium borohydride, and perchlorate), electrolytes, and various additives (such as film-forming agents, flame retardants, and overcharge protection agents).

[0003] Electrodeless sodium-ion batteries are an innovative battery technology. Their core lies in omitting the traditional negative electrode active material (i.e., they contain no negative electrode active material). Instead, they utilize sodium ions released from the positive electrode during charging to directly deposit on the negative electrode current collector (such as aluminum foil) to form the negative electrode, creating a rechargeable sodium source. During the first charge, sodium ions gain electrons at the anode side and deposit metallic sodium on the current collector surface to form a sodium metal phase. During discharge, the metallic sodium can revert to sodium ions and return to the positive electrode, achieving cyclic charging and discharging. Compared to other sodium rechargeable batteries, electrodeless sodium-ion batteries, lacking a negative electrode active material layer, can accommodate more positive electrode active material, resulting in higher energy density. The electrodeless design simplifies the battery structure, further reducing production costs and increasing energy density.

[0004] Electrodeless sodium-ion batteries (actually using aluminum foil current collectors as the negative electrode, but without hard carbon coating) are an effective method to improve energy density, with the following two advantages: 1. Na and Al do not undergo alloying reaction; during charging and discharging, Na+ reacts directly on the Al foil surface. + The interconversion of Na and sodium saves the volume and weight occupied by hard carbon in traditional solutions, thus directly improving energy density. 2. There is no need to consider the consumption of active sodium ions during the first charge-discharge process of hard carbon, thereby improving energy density by increasing the initial efficiency.

[0005] A sodium-ion battery is typically assembled from a positive electrode, a separator, a negative electrode, and an electrolyte. For example, an electrode assembly can be formed by stacking the positive electrode, the separator (which acts as a barrier between the positive and negative electrodes), and the negative electrode. This assembly is then placed in outer packaging, dried, and injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a sodium-ion battery is obtained.

[0006] However, in the fabrication of electrodeless sodium-ion batteries, aluminum foil is required as the negative electrode. Aluminum is relatively soft and only about 10 micrometers thick, resulting in low mechanical strength. In traditional electrodeless battery fabrication processes, the aluminum foil undergoes wrinkling, damage, and contamination during cutting, transfer, and stacking. This can easily lead to changes in the morphology of the aluminum foil before and after electrode assembly, severely affecting battery consistency and posing potential risks to battery performance and safety. These problems urgently need to be addressed. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the defects in the existing negative electrode sodium-ion battery preparation method, in which aluminum foil as the negative electrode is subject to wrinkling, damage and contamination, which easily leads to changes in the shape of aluminum foil before and after electrode assembly and affects the consistency of the battery. The present invention provides a composite aluminum foil, composite electrode sheet and negative electrode sodium-ion battery preparation method.

[0008] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0009] This invention provides a composite aluminum foil, comprising a substrate and positive electrode regions and negative electrode regions alternately disposed on both sides of the substrate, wherein an aluminum foil layer is disposed in both the negative electrode region and the positive electrode region.

[0010] The positive electrode regions on both sides of the substrate correspond to each other, and the negative electrode regions correspond to each other.

[0011] In this invention, the substrate can be conventional in the battery industry, such as PET film.

[0012] In this invention, "the positive electrode regions on both sides of the substrate correspond to each other, and the negative electrode regions correspond to each other" generally means that the positive electrode region on one side of the substrate corresponds to the positive electrode region on the other side of the substrate, and the negative electrode region on one side of the substrate corresponds to the negative electrode region on the other side of the substrate.

[0013] In this invention, double-sided aluminum foil layers are provided on both the positive and negative electrode regions on both sides of the substrate.

[0014] In this invention, preferably, the dimensions and areas of the corresponding positive electrode regions on both sides of the substrate are equal.

[0015] In this invention, preferably, the dimensions and areas of the corresponding negative electrode regions on both sides of the substrate are equal.

[0016] In this invention, on one side of the substrate, the distance between the negative electrode region and the positive electrode region is equal.

[0017] In this invention, the distance between the negative electrode region and the positive electrode region on one side of the substrate can be 2-3 mm.

[0018] In this invention, the composite aluminum foil can be used in a negative electrode-free sodium-ion battery. The negative electrode region consists only of an aluminum foil layer without any negative electrode active material, while the aluminum foil in the positive electrode region is coated with a positive electrode active material.

[0019] In this invention, the dimensions of the positive electrode region and the negative electrode region can be conventional in the art. In a preferred embodiment, the dimensions of the positive electrode region, the negative electrode region, and the separator size are as follows: Figure 1 As shown.

[0020] The present invention provides a method for preparing the composite aluminum foil, for example, by depositing aluminum on both sides of the substrate by PVD physical vapor deposition to form the positive electrode region and the negative electrode region, thereby obtaining the composite aluminum foil.

[0021] The present invention provides a composite electrode sheet, which includes the composite aluminum foil, wherein a positive electrode active material layer is provided on the positive electrode region of the composite aluminum foil.

[0022] In this invention, the preparation method of the positive electrode active material layer can be conventional in the art, generally involving coating the positive electrode slurry onto the aluminum foil layer in the positive electrode region. After coating, drying, rolling, and slitting are generally performed.

[0023] The coating process for the positive electrode slurry can be conventional in the art, such as transfer coating, spray coating, or gravure printing.

[0024] The coating thickness of the positive electrode slurry can be adjusted according to actual conditions.

[0025] The drying conditions can be those conventional in the field.

[0026] The purpose of the rolling is generally to roll the coated positive electrode active material to a suitable compaction density, which is a routine operation in the field.

[0027] In this invention, the material of the positive electrode active material layer can be made from conventional positive electrode active materials in the art.

[0028] In a preferred embodiment, the positive electrode slurry formulation includes: 95% NFPP, 1.5% Super P, 0.5% MWCNT multi-walled carbon nanotubes, and 3.0% PVDF, where each percentage represents the mass percentage of each component's dry weight relative to the total dry weight of the raw materials in the formulation. A planetary mixer is used to thoroughly mix all components in the formulation. The positive electrode slurry is coated on a single side with a surface density of 150 g / m² on the positive electrode sheet. 2 .

[0029] This invention also provides a method for preparing a negative electrode-free sodium-ion battery, which includes the following steps:

[0030] (1) A diaphragm is provided on both sides of the composite electrode to form a composite structure of "diaphragm-composite electrode-diaphragm";

[0031] (2) The composite structure of “diaphragm-composite electrode-diaphragm” is assembled in a Z-shape to form a stacked bare cell;

[0032] (3) The stacked bare cells are installed into the casing, and after top and side sealing, liquid injection and formation processes, a sodium-ion battery without negative electrode is obtained.

[0033] In step (1), the diaphragm can be a conventional diaphragm in the art. The size of the diaphragm can be conventional in the art.

[0034] In step (1), the composite structure of "diaphragm-composite electrode-diaphragm" is preferably obtained by the following steps: take two diaphragms, apply adhesive to one side of each diaphragm, with the adhesive side adjacent to both sides of the composite electrode, apply heat, and the two diaphragms are completely adhered to the surface of the composite electrode to form the structure of "diaphragm-composite electrode-diaphragm".

[0035] The amount of adhesive applied to the diaphragm can be conventional in the art. The adhesive can be a conventional adhesive liquid in the art, such as PVDF.

[0036] The adhesive in the single-sided coated diaphragm has adhesive properties. After the coated diaphragm is heat-applied to the composite electrode, it can become an integral part of the composite electrode, forming a "diaphragm-composite electrode-diaphragm" structure. This structure can protect the electrode and is also a pre-operation for subsequent Z-shaped stacking.

[0037] The hot compress procedure can be conventional in the art, for example, at a certain temperature (e.g., 45~100℃) and under a certain pressure (40~80 kgf / cm). 2 The heat application temperature can be 60℃. The pressure during the heat application can be 60 kgf / cm². 2 .

[0038] In step (1), the composite structure of "diaphragm-composite electrode-diaphragm" is generally die-cut into electrode tabs using conventional methods.

[0039] In step (2), the stacking process can be carried out by gravity or mechanically.

[0040] In step (2), before the lamination assembly, the composite structure of “diaphragm-composite electrode-diaphragm” in step (1) can be connected and rolled into a roll, or a single “diaphragm-composite electrode-diaphragm” composite structure can be entered into the lamination process.

[0041] In step (3), the outer shell can be a soft shell or a square aluminum shell.

[0042] In step (3), there are generally further processes such as capacity separation and sorting after the formation process.

[0043] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0044] The reagents and raw materials used in this invention are all commercially available.

[0045] The positive and progressive effects of this invention are as follows:

[0046] The composite electrode of this invention can be assembled into an electrode assembly or cell to be packaged by "Z" folding, thus producing a corresponding negative electrode-free sodium-ion battery (in the traditional manufacturing process of negative electrode-free sodium-ion batteries, "Z" folding is only for the separator, while the positive and negative electrode sheets used for stacking are separate). This not only effectively improves the production efficiency of the electrode assembly or cell assembly section and avoids disruption of the production rhythm due to abnormalities such as aluminum foil breakage during stacking and winding, but also has a high yield. By controlling the processing, the consistency of the production process can be improved, greatly reducing the safety hazards of the battery in the end use.

[0047] In addition, in the composite electrode of the present invention, the aluminum foil has a coated diaphragm on both sides as a protective layer, which not only effectively prevents the highly active metal surface from being contaminated, but also provides the aluminum foil with a certain mechanical strength. Attached Figure Description

[0048] Figure 1 Part A is the negative electrode. Figure 1 Part B is the positive electrode (blue represents the positive electrode active material). Figure 1 Part C is the diaphragm, and a, b, c, d, e, and f represent the dimensions.

[0049] Figure 2 This is a top view schematic diagram of the composite aluminum foil structure, in which, Figure 2 Part A refers to the negative electrode region. Figure 2 Part B refers to the positive electrode region, 1 is the PET film, and b and e represent the size.

[0050] Figure 3 This is a front view schematic diagram of the composite aluminum foil structure, in which, Figure 3 Part A refers to the negative electrode region. Figure 3 Part B refers to the positive electrode region, 1 is the PET film, and b and e represent the size.

[0051] Figure 4 This is a schematic diagram of the coating process in the preparation of composite electrodes, where 1 represents the PET film, and b, e, and c represent dimensions.

[0052] Figure 5This is a schematic diagram of the structure of the product after the tabs are die-cut during the preparation of composite electrodes. In this diagram, 1 represents the PET film and c represents the size.

[0053] Figure 6 Part A is a schematic diagram of the Z-shaped stacked assembly. In this diagram, the dark blue lines represent the positive electrode sheets coated with positive active material, the light gray lines represent aluminum foil without negative active material, and the black lines represent PET separators. Figure 6 Part B is a schematic diagram of the structure of the stacked core, where the dark gray area represents the diaphragm and the light gray areas at the top and bottom represent aluminum foil.

[0054] Figure 7 The charge-discharge cycle curve of a 1Ah sodium-ion battery without a negative electrode at a current of 1C is shown. Detailed Implementation

[0055] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0056] 1. Preparation of composite electrodes:

[0057] (1) Based on common knowledge in this field, determine the dimensions of the positive electrode, negative electrode, and separator of the negative electrode-less sodium-ion battery, and simultaneously determine the dimensions of the foil material in the tab area of ​​the stacked battery. The dimensions of each part are as follows: Figure 1 As shown. Among them, Figure 1 Part A is the negative electrode. Figure 1 Part B is the positive electrode (blue represents the positive electrode active material). Figure 1 Part C is the diaphragm. The dimensions of a, b, c, d, e, and f are standard, and the dimensions must satisfy b > e, f > ac > d. Generally speaking, b and e represent the width, and a and d represent the length.

[0058] (2) Using commercially available PET film as a substrate, negative and positive electrode regions are alternately arranged on both sides of the PET film. Both the negative and positive electrode regions are provided with aluminum foil layers (aluminum can be deposited onto the substrate using PVD), thus producing a composite aluminum foil. Specifically, the positive electrode region on one side of the PET film corresponds to the positive electrode region on the other side, and the negative electrode region on one side of the PET film corresponds to the negative electrode region on the other side. That is, double-sided aluminum foil layers are provided in both the positive and negative electrode regions of the PET film. On one side of the PET film, the distance between the negative and positive electrode regions is equal, typically 2-3 mm.

[0059] Figure 2 This is a top view schematic diagram of the composite aluminum foil structure. Among them, Figure 2 Part A refers to the negative electrode region. Figure 2In the diagram, part B refers to the positive electrode region, 1 represents the PET film, and the dimensional requirements for b and e are the same as those for the positive electrode region. Figure 1 Consistent. The positive electrode regions are equal in size and area, and the negative electrode regions are equal in size and area.

[0060] Figure 3 This is a front view schematic diagram of the composite aluminum foil structure. Among them, Figure 3 Part A refers to the negative electrode region. Figure 3 Part B refers to the positive electrode region, 1 is the PET film, and the size requirements of b and e are the same as those of the positive electrode region. Figure 1 Consistent. The positive electrode regions are equal in size and area, and the negative electrode regions are equal in size and area. Through Figure 3 It can be seen that double-sided aluminum foil layers are set on both the upper and lower sides of the PET film, in both the positive and negative electrode areas.

[0061] (3) According to Figure 1-3 The design, according to Figure 4 The proposed method involves coating the positive electrode slurry on both sides of the PET electrode, drying it in an electric oven, rolling it, and finally cutting it at the middle of the gap along the positive electrode coating direction. Figure 4 (At the dotted line), a composite electrode is formed. Coating can be a conventional transfer process, and the coating thickness, drying conditions, and rolling conditions can all be conventional.

[0062] Figure 4 This is a schematic diagram of the coating process in the fabrication of composite electrodes. Wherein, 1 represents the PET film, and the dimensional requirements of b and e are... Figure 1 Consistent. The size and area of ​​the coating on the positive electrode region are equal. Dimension c is the tab size determined during cell design; after stacking, all c portions overlap, such as... Figure 6 The upper and lower gray areas shown in section B.

[0063] (4) Take two diaphragms and apply adhesive to one side of each diaphragm. The amount of adhesive applied can be conventional in this field. Place a commercially available diaphragm on each side of the composite electrode, with the adhesive-coated side of the diaphragm adjacent to the composite electrode. The size requirements of the diaphragms are the same as those in this field. Figure 1 The requirements for a, d, c, and f are consistent. Generally, the membrane width extends beyond the positive electrode region ( Figure 1 (in the d direction), and the part exceeding the d direction is symmetrical vertically.

[0064] The diaphragms on both sides of the composite electrode are heat-applied, causing them to adhere completely to the electrode surface, forming a "diaphragm-composite electrode-diaphragm" structure. The heat application temperature is 60℃, and the pressure is 60 kgf / cm². 2 .

[0065] (5) The composite electrode sheet with the diaphragm is die-cut into tabs, and the structural diagram is shown below. Figure 5As shown.

[0066] Figure 5 This is a schematic diagram of the product structure after the tabs are die-cut during the composite electrode fabrication process. Wherein, 1 represents the PET film, and c has the same size requirements as... Figure 1 Consistent. The size and area of ​​the coating on the positive electrode region are equal. The size and area of ​​the coating on the negative electrode region are equal.

[0067] 2. Preparation of a sodium-ion battery without a negative electrode:

[0068] (6) According to Figure 6 The method described in Part A involves zigzag lamination assembly, where the lamination process is driven solely by gravity (mechanical propulsion is also possible, and the process is versatile). Before lamination, [the following steps can be taken]. Figure 4 All the prepared composite electrodes are connected and rolled into a roll, or individual composite electrodes can be used in the stacking process. Then the stacked core is put into a soft-pack shell (or a square aluminum shell), and after top and side sealing, electrolyte injection, formation, capacity testing, and sorting, a negative electrode-free sodium-ion battery is obtained.

[0069] Figure 6 Part A is a schematic diagram of a Z-shaped stacked assembly. The dark blue lines represent the positive electrode sheets coated with the positive active material, the light gray lines represent aluminum foil without the negative active material, and the black lines represent the PET separator.

[0070] Figure 6 Part B is a schematic diagram of the structure of the stacked core. The dark gray area represents the diaphragm, and the light gray areas at the top and bottom represent the aluminum foil.

[0071] Example 1

[0072] Composite electrodes and a negative electrode-free sodium-ion battery were prepared according to the above method. Specifically,

[0073] The positive electrode slurry formulation includes: 95% NFPP, 1.5% Super P, 0.5% MWCNT (multi-walled carbon nanotubes), and 3.0% PVDF. All percentages represent the dry weight of each component relative to the total dry weight of the raw materials. A planetary mixer is used to thoroughly mix all components. The positive electrode slurry is coated on one side with a surface density of 150 g / m². 2 .

[0074] The following materials were sourced: Aluminum foil from Shenzhen Yuqiang New Materials Co., Ltd.; NFPP (sodium iron pyrophosphate), purchased from Shenzhen Jiana Energy Technology Co., Ltd., model JNFP-1; Super P, purchased from Temico, model C45; MWCNT (multi-walled carbon nanotubes), purchased from Jiangsu Xicheng; PVDF, purchased from Solvay, model 5130. Electrolyte: 5g added, purchased from Shenzhen Jiana Energy Technology Co., Ltd., grade N59.

[0075] Effect test:

[0076] Full battery charge and discharge test equipment: Xinwei 5V6A test cabinet; 1Ah cell, charge and discharge voltage range 3.4~1.5V, 1C constant current and constant voltage charging, 0.05C cutoff, rest for 10min, 1C discharge, 518 cycles, capacity retention rate 70.93%.

[0077] Figure 7 Table 1 shows the charge-discharge cycle curves of a 1Ah negative electrode-free sodium-ion battery at a current of 1C. The specific test data are shown in Table 1.

[0078] Table 1

[0079]

Claims

1. A composite aluminum foil, characterized in that, It includes a substrate and positive electrode regions and negative electrode regions alternately disposed on both sides of the substrate, wherein both the negative electrode region and the positive electrode region are provided with an aluminum foil layer. The positive electrode regions on both sides of the substrate correspond to each other, and the negative electrode regions correspond to each other.

2. The composite aluminum foil as described in claim 1, characterized in that, The dimensions and areas of the corresponding positive electrode regions on both sides of the substrate are equal. And / or, the dimensions and areas of the corresponding negative electrode regions on both sides of the substrate are equal.

3. The composite aluminum foil as described in claim 1, characterized in that, On one side of the substrate, the distance between the negative electrode region and the positive electrode region is equal; And / or, on one side of the substrate, the distance between the negative electrode region and the positive electrode region is 2-3 mm; And / or, the substrate is a PET film.

4. A composite electrode, characterized in that, It includes the composite aluminum foil as described in any one of claims 1-3, wherein a positive electrode active material layer is provided on the positive electrode region of the composite aluminum foil.

5. The composite electrode as described in claim 4, characterized in that, The preparation method of the positive electrode active material layer includes the following steps: coating the positive electrode slurry onto the aluminum foil layer in the positive electrode region, and then drying and rolling it after coating.

6. The composite electrode as described in claim 5, characterized in that, The coating process for the positive electrode paste includes transfer coating, spray coating, or gravure printing. And / or, the positive electrode slurry formulation includes: 95% NFPP, 1.5% Super P, 0.5% multi-walled carbon nanotubes and 3.0% PVDF, wherein each percentage is the mass percentage of the dry weight of each component relative to the total dry weight of the raw materials in the formulation; And / or, on the positive electrode active material layer, the single-sided areal density of the positive electrode slurry coating is 140-160 g / m². 2 For example, 150g / m 2 .

7. A method for preparing a negative electrode-free sodium-ion battery, characterized in that, It includes the following steps: (1) A diaphragm is provided on both sides of the composite electrode as described in any one of claims 4-6 to form a composite structure of "diaphragm-composite electrode-diaphragm"; (2) The composite structure of "diaphragm-composite electrode-diaphragm" is assembled in a Z-shape to form a stacked bare cell; (3) The stacked bare cells are installed into the casing, and after top and side sealing, liquid injection and formation processes, a sodium-ion battery without negative electrode is obtained.

8. The method for preparing a negative electrode-free sodium-ion battery as described in claim 7, characterized in that, In step (1), the composite structure of "diaphragm-composite electrode-diaphragm" is obtained by the following steps: take two diaphragms, apply adhesive to one side of each diaphragm, with the adhesive side adjacent to both sides of the composite electrode, apply heat, and the two diaphragms are completely adhered to the surface of the composite electrode to form the structure of "diaphragm-composite electrode-diaphragm".

9. The method for preparing a negative electrode-free sodium-ion battery as described in claim 8, characterized in that, The adhesive used for single-sided coating is PVDF; And / or, the method of applying heat includes the following steps: applying heat at a temperature of 45~100℃ for a period of 40~80 kgf / cm². 2 Apply heat under pressure.

10. The method for preparing a negative electrode-free sodium-ion battery as described in claim 7, characterized in that, In step (2), during the stacking assembly process, the stacking process is propelled by gravity or mechanical force. And / or, in step (2), before the stack assembly, the composite structure of "diaphragm-composite electrode-diaphragm" from step (1) is connected and rolled up.

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