An aluminum foil for a sodium-ion battery negative electrode, a negative electrode sheet, and a sodium-ion battery.

Abstract

This invention belongs to the field of sodium-ion battery technology, specifically relating to an aluminum foil for a sodium-ion battery negative electrode, a negative electrode sheet, and a sodium-ion battery. The aluminum foil for a sodium-ion battery negative electrode provided by this invention has a pre-treatment coating on its surface. This pre-treatment coating is formed by coating and drying a coating liquid. The coating liquid is composed of polyacrylic acid, polyvinylpyrrolidone, sodium oxalate, and water. The mass ratio of polyacrylic acid, polyvinylpyrrolidone, and sodium oxalate is (84~94):(3~8):(3~8). This invention, by setting a pre-treatment coating with a specific composition on the surface of the aluminum foil, can significantly improve the peel strength between the hard carbon negative electrode material and the aluminum foil in sodium-ion batteries, and improve the energy density and cycle performance of the battery. It solves the problem of poor adhesion of existing hard carbon negative electrode slurry coatings to the aluminum foil surface, resulting in poor battery energy density and cycle performance. It has broad application prospects in the field of sodium-ion battery manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to an aluminum foil for a sodium-ion battery negative electrode, a negative electrode sheet, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries, as an important direction for next-generation energy storage technology, have attracted widespread attention due to their advantages such as abundant resources and low cost. Currently, the negative electrode of sodium-ion batteries typically uses aluminum foil as the current collector, and a slurry containing hard carbon active material is coated on the surface of the aluminum foil to form the negative electrode sheet.

[0003] However, during the coating process of the negative electrode hard carbon slurry, the low dyne value of the aluminum foil surface leads to poor adhesion of the slurry to the aluminum foil surface. Simultaneously, due to the surface tension of the slurry liquid, the slurry liquid on both sides of the aluminum foil edge surface is prone to flow during drying, resulting in thick edges on the aluminum foil and even electrode edge curling, severely affecting the battery manufacturing yield and electrochemical performance. Furthermore, during the first charge and discharge process, sodium-ion batteries irreversibly consume a large amount of sodium ions from the positive electrode to form a solid electrolyte interphase (SEI) film, resulting in a lower overall energy density of the battery and affecting the cycle performance and lifespan of the sodium-ion battery.

[0004] Therefore, improving the peel strength between hard carbon slurry and aluminum foil current collector, and enhancing the energy density and cycle performance of sodium-ion batteries, is a technical challenge that urgently needs to be addressed in the current sodium-ion battery technology field. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide an aluminum foil for a sodium-ion battery negative electrode, a negative electrode sheet, and a sodium-ion battery. This invention, by applying a pre-treatment coating of a specific composition to the surface of the aluminum foil, can significantly improve the peel strength between the hard carbon negative electrode material and the aluminum foil in sodium-ion batteries, and improve the energy density and cycle performance of the battery. This solves the problems of poor adhesion of existing hard carbon negative electrode slurry coatings to the aluminum foil surface, resulting in suboptimal battery energy density and cycle performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an aluminum foil for a sodium-ion battery negative electrode, wherein the surface of the aluminum foil is coated with a pre-treatment coating; the pre-treatment coating is formed by coating and drying a coating liquid; the coating liquid is composed of polyacrylic acid, polyvinylpyrrolidone, sodium oxalate and water; the mass ratio of polyacrylic acid, polyvinylpyrrolidone and sodium oxalate is (84~94):(3~8):(3~8).

[0007] To ensure the coatability of the coating liquid, as a preferred embodiment, the solid content of the coating liquid is 2-8 wt%, more preferably 3 wt%.

[0008] As a preferred embodiment, the polyacrylic acid has a weight-average molecular weight of 800,000 to 1,200,000; and the polyvinylpyrrolidone has a weight-average molecular weight of 40,000 to 80,000.

[0009] As a preferred embodiment, the mass ratio of polyacrylic acid, polyvinylpyrrolidone, and sodium oxalate is 90:5:5.

[0010] As a preferred embodiment, the drying temperature is 80~140℃, and the time is 2~20min. The thickness of the pretreatment coating is 1~10μm, more preferably 2~5μm. Controlling the thickness of the pretreatment coating within a certain range has minimal negative impact on the total energy density of the battery, while ensuring the bonding effect. This facilitates a high-strength chemical bond between the coating and the current collector, improving interfacial adhesion enhancement and sodium replenishment.

[0011] As a preferred embodiment, the method for preparing the aluminum foil for the negative electrode of the sodium-ion battery includes the following steps: dissolving polyacrylic acid, polyvinylpyrrolidone, and sodium oxalate in water according to a mass ratio to obtain a coating solution; uniformly coating the coating solution onto the surface of the aluminum foil to be treated, and drying it to form a pre-treated coating, thereby obtaining the aluminum foil for the negative electrode of the sodium-ion battery.

[0012] Secondly, the present invention provides a sodium-ion battery negative electrode sheet, comprising the above-mentioned aluminum foil for sodium-ion battery negative electrode and a negative electrode material layer coated on the aluminum foil.

[0013] As a preferred embodiment, the negative electrode material layer comprises the following components in the following mass ratio: 9.0-9.8 parts hard carbon, 0.1-0.4 parts conductive agent, 0.02-0.1 parts sodium carboxymethyl cellulose, 0.1-0.5 parts styrene-butadiene rubber, and 0.02-0.2 parts polyacrylic acid. In this invention, both the pretreatment coating and the negative electrode material layer contain polyacrylic acid, which is a homogeneous material, enabling homogeneous matching between interfaces and enhancing the consistency of interlayer bonding.

[0014] As a preferred embodiment, the conductive agent is selected from at least one of conductive graphite, conductive carbon black, carbon nanotubes, and acetylene black.

[0015] As a preferred embodiment, the method for preparing the negative electrode sheet of the sodium-ion battery includes the following steps: dissolving hard carbon, conductive agent, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid in water according to a mass ratio to obtain a negative electrode slurry; coating the negative electrode slurry onto aluminum foil for the negative electrode of the sodium-ion battery, and drying it to form a negative electrode material layer, thereby obtaining the negative electrode sheet of the sodium-ion battery.

[0016] As a preferred embodiment, the solid content of the negative electrode slurry is 8-15 wt%, more preferably 10 wt%.

[0017] Thirdly, the present invention provides a sodium-ion battery, comprising a positive electrode, a separator, an electrolyte, and a negative electrode; wherein the negative electrode is the aforementioned sodium-ion battery negative electrode.

[0018] As a preferred embodiment, the positive electrode sheet includes a positive electrode material layer; the positive electrode material layer includes the following components in the following mass ratio: 9-9.8 parts of positive electrode active material, 0.05-0.5 parts of conductive agent, and 0.1-0.5 parts of polyvinylidene fluoride.

[0019] As a preferred embodiment, the N / P ratio of the sodium-ion battery is 1.0 to 1.3.

[0020] As a preferred embodiment, the positive electrode active material is selected from at least one of ternary positive electrode materials, polyanionic materials, and Prussian blue materials; the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and conductive graphite.

[0021] The technical solution of the present invention has the following advantages and beneficial effects: (i) Significantly Improved Peel Strength: The aluminum foil surface naturally contains a dense and chemically inert alumina film, making it difficult for subsequent adhesives and current collectors to form an effective bond. In the pretreatment coating of this invention, sodium oxalate, as a surface modifier, can undergo a mild complexation etching reaction with the alumina on the aluminum foil surface. This creates nanoscale micropores and uneven morphology on the aluminum foil surface without damaging the aluminum foil matrix structure, providing physical intercalation and mechanical anchoring sites for subsequent adhesives and hard carbon particles, avoiding the easy detachment problem caused by simple physical adsorption. Furthermore, the etching reaction peels off the inert oxide layer, exposing a large number of active aluminum hydroxyl groups, and the carboxylate ions in sodium oxalate adsorb and bond to the aluminum foil surface, introducing abundant carboxyl active sites, further activating the aluminum foil interface and eliminating interfacial bonding barriers.

[0022] Meanwhile, polyacrylic acid, as the core binder, plays a bidirectional bridging role, achieving a high-strength chemical bond between hard carbon particles and modified aluminum foil. The polyacrylic acid molecular chain contains a large number of high-density carboxyl functional groups. On one hand, it can undergo dehydration esterification and hydrogen bonding with the hydroxyl groups generated after activation with sodium oxalate on the aluminum foil surface. It can also form stable metal-carboxyl coordination bonds with aluminum ions on the aluminum foil surface. Through the combination of covalent bonds, coordination bonds, and hydrogen bonds, a strong chemical adhesion layer is formed on the aluminum foil surface, completely breaking through the upper limit of physical adsorption bonding strength. On the other hand, the surface of hard carbon particles itself has oxygen-containing functional groups and defect sites such as hydroxyl and carboxyl groups. The carboxyl groups of polyacrylic acid can form strong intermolecular hydrogen bonds with them. At the same time, the long polymer chains can fully entangle and coat individual hard carbon particles, bonding the dispersed hard carbon particles together into a complete whole. Then, through the bridging effect of its own molecular chains, the entire hard carbon negative electrode layer is firmly anchored to the aluminum foil surface, achieving a high-strength chemical bond between the current collector, binder, and negative electrode particles. Experimental data show that the negative electrode sheet prepared using the aluminum foil of this invention has a significantly improved peel strength compared to aluminum foil without pretreatment coating.

[0023] (ii) Improved energy density: By introducing sodium oxalate on the surface of aluminum foil, the present invention can form a stable SEI film through electrochemical reaction during battery charging and discharging, providing additional sodium ion replenishment, effectively offsetting the irreversible consumption of sodium elements from the positive electrode by the negative electrode, thereby improving the overall energy density of the battery.

[0024] (III) Improved Cycle Performance: By introducing polyacrylic acid, this invention creates a flexible three-dimensional network structure that effectively buffers the volume expansion and contraction stress of hard carbon particles during charge and discharge, maintaining the integrity of the electrode structure and the long-term stability of interfacial adhesion. Simultaneously, sodium oxalate forms a thin and stable oxalate passivation film on the aluminum foil surface, preventing electrolyte corrosion and interface erosion, while also stabilizing the active groups at the interface and ensuring the long-term effectiveness of the adhesion. Experimental data show that the sodium-ion battery of this invention exhibits excellent cycle performance, retaining over 97% of its capacity after 1000 cycles.

[0025] Therefore, by setting a pre-treatment coating on the surface of aluminum foil, the present invention can significantly improve the peel strength between the hard carbon anode material of sodium-ion battery and aluminum foil through the synergistic effect of sodium oxalate and polyacrylic acid, and improve the energy density and cycle performance of the battery, which has broad application prospects in the field of sodium-ion battery preparation. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described clearly and completely below in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Without departing from the scope or spirit of this invention, those skilled in the art can make various improvements and changes to the specific embodiments described in this specification, which will be obvious to those skilled in the art.

[0027] Unless otherwise stated, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While only preferred methods and materials have been described in this invention, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. Furthermore, the terms "comprising," "including," "having," "containing," etc., as used in this invention are open-ended, meaning they include but are not limited to.

[0028] In this invention, styrene-butadiene rubber (SBR) is used as a polymeric binder. The invention does not impose any particular limitation on its type; those skilled in the art can conventionally select SBR types suitable for sodium-ion batteries. Optional SBRs include AL-1002, AL-3001A, and SN-307R. Specifically, in the following embodiments of this invention, the SBR used is SN-307R, with a solid content of 40-50%.

[0029] In the following embodiments of the present invention, the aluminum foil to be processed is a high-purity (≥99.9%) battery-grade aluminum foil with a thickness of 10~12μm.

[0030] In this invention, the hard carbon can be any commercially available type commonly used in the sodium-ion battery field, and this invention does not impose any particular restrictions on it. Optional hard carbon types include GHC-C300A, GHC-D300, GHC-B300, BHC-400, HC-320, etc. Specifically, in the following embodiments of this invention, the hard carbon type used is GHC-B300.

[0031] In this invention, polyvinylidene fluoride (PVDF) is a common binder in the battery field, and this invention does not impose any particular limitations on it. For example, optional PVDFs include Kynar 761A, Kynar HSV900, Kynar 740, etc. Specifically, in the following embodiments of this invention, the PVDF used is Kynar HSV900.

[0032] Example 1 This embodiment provides an aluminum foil for a sodium-ion battery negative electrode, the preparation method of which includes the following steps: dissolving polyacrylic acid (PAA), polyvinylpyrrolidone (PVP), and sodium oxalate in water at a mass ratio of 90:5:5 to prepare a coating solution with a solid content of 3wt%. The coating solution is then applied to both sides of the aluminum foil surface to be treated, and dried at 120°C for 5 minutes to form a pre-treated coating with a thickness of 2μm, resulting in the pre-treated aluminum foil, which is the aluminum foil for the sodium-ion battery negative electrode of this embodiment. The weight-average molecular weight (M) of the polyacrylic acid is... w The weight-average molecular weight (M) of polyvinylpyrrolidone is 1 million; w The purity of sodium oxalate is 99.9%, with a value of 60,000.

[0033] This embodiment also provides a sodium-ion battery negative electrode sheet, comprising the aforementioned aluminum foil for sodium-ion battery negative electrodes and a negative electrode material layer coated on the aluminum foil. The preparation method of this sodium-ion battery negative electrode sheet includes the following steps: mixing hard carbon, conductive carbon black, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA) in a mass ratio of 9.55:0.15:0.04:0.20:0.06, and then adding water to prepare a negative electrode slurry with a solid content of 10 wt%. The negative electrode slurry is then coated on both sides of the pretreated aluminum foil surface, and the surface density of the coated single side is 70 g / m². 2 The sodium-ion battery negative electrode sheet of this embodiment is then dried and rolled to obtain the electrode. The weight-average molecular weight (M) of polyacrylic acid is... w The figure is 1 million.

[0034] This embodiment also provides a sodium-ion battery, including a positive electrode, a separator, an electrolyte, and a negative electrode; the negative electrode is the aforementioned sodium-ion battery negative electrode. The preparation method of the positive electrode includes the following steps: a composite sodium iron phosphate (Na4Fe3(PO4)2P2O7, NFPP), conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 9.55:0.15:0.30, and then N-methylpyrrolidone (NMP) is added to prepare a positive electrode slurry with a solid content of 60 wt%. The positive electrode slurry is coated on both sides of a positive electrode aluminum foil, and the surface density of the coated side is 160 g / m³. 2 The positive electrode sheet is then dried and rolled.

[0035] The positive electrode, separator, and negative electrode obtained above are stacked sequentially to form a battery cell, and then an electrolyte is injected. After encapsulation and formation processes, the sodium-ion battery of this embodiment is obtained. The electrolyte consists of 1.0 mol / L sodium hexafluorophosphate (NaPF6), and the solvent is a mixed solvent of propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 25:35:40. The N / P ratio of the sodium-ion battery is controlled between 1.0 and 1.3.

[0036] Example 2 This embodiment provides an aluminum foil for the negative electrode of a sodium-ion battery. Its preparation method is basically the same as that of Example 1, except that the mass ratio of polyacrylic acid, polyvinylpyrrolidone and sodium oxalate is adjusted to 94:3:3, and the other conditions are the same as those of Example 1.

[0037] This embodiment also provides a sodium-ion battery negative electrode sheet and a sodium-ion battery. Except that the aluminum foil is the same as the aluminum foil for sodium-ion battery negative electrode prepared in this embodiment, the other conditions are the same as in Embodiment 1.

[0038] Example 3 This embodiment provides an aluminum foil for the negative electrode of a sodium-ion battery. Its preparation method is basically the same as that of Example 1, except that the solid content of the coating solution is adjusted to 4 wt%, and the other conditions are the same as those of Example 1.

[0039] This embodiment also provides a sodium-ion battery negative electrode sheet and a sodium-ion battery. Except that the aluminum foil is the same as the aluminum foil for sodium-ion battery negative electrode prepared in this embodiment, the other conditions are the same as in Embodiment 1.

[0040] Example 4 This embodiment provides an aluminum foil for the negative electrode of a sodium-ion battery. Its preparation method is basically the same as that of Embodiment 1, except that the drying temperature is adjusted to 130°C, and the other conditions are the same as those of Embodiment 1.

[0041] This embodiment also provides a sodium-ion battery negative electrode sheet and a sodium-ion battery. Except that the aluminum foil is the same as the aluminum foil for sodium-ion battery negative electrode prepared in this embodiment, the other conditions are the same as in Embodiment 1.

[0042] Example 5 This embodiment provides an aluminum foil for the negative electrode of a sodium-ion battery. Its preparation method is basically the same as that of Embodiment 1, except that the drying time is adjusted to 10 min, and the other conditions are the same as those of Embodiment 1.

[0043] This embodiment also provides a sodium-ion battery negative electrode sheet and a sodium-ion battery. Except that the aluminum foil is the same as the aluminum foil for sodium-ion battery negative electrode prepared in this embodiment, the other conditions are the same as in Embodiment 1.

[0044] Comparative Example 1 This comparative example provides an aluminum foil for a sodium-ion battery negative electrode, which is an untreated aluminum foil. This aluminum foil does not contain a pre-treated material layer and is subsequently directly coated with a negative electrode slurry.

[0045] The comparative example also provides a sodium-ion battery negative electrode sheet and a sodium-ion battery, except that the aluminum foil used in the comparative example is the untreated carbon-coated aluminum foil, and the other conditions are the same as in Example 1.

[0046] Comparative Example 2 This comparative example provides an aluminum foil for the negative electrode of a sodium-ion battery, the preparation method of which is basically the same as that of Example 1, except that sodium oxalate is not added to the coating solution. The preparation process of the coating solution is adjusted as follows: polyacrylic acid and polyvinylpyrrolidone are dissolved in water at a mass ratio of 90:10 to prepare a coating solution with a solid content of 3wt%, and the other conditions are the same as in Example 1.

[0047] The comparative example also provides a sodium-ion battery negative electrode sheet and a sodium-ion battery, except that the aluminum foil used in the comparative example is the same as that in Example 1.

[0048] Comparative Example 3 This comparative example provides an aluminum foil for the negative electrode of a sodium-ion battery, the preparation method of which is basically the same as that of Example 1, except that polyacrylic acid is not added to the coating solution. The preparation process of the coating solution is adjusted as follows: polyvinylpyrrolidone and sodium oxalate are dissolved in water at a mass ratio of 95:5 to prepare a coating solution with a solid content of 3wt%, and the other conditions are the same as in Example 1.

[0049] The comparative example also provides a sodium-ion battery negative electrode sheet and a sodium-ion battery, except that the aluminum foil used in the comparative example is the same as that in Example 1.

[0050] Comparative Example 4 This comparative example provides an aluminum foil for the negative electrode of a sodium-ion battery, and its preparation method is the same as that in Example 1.

[0051] The comparative example also provides a sodium-ion battery negative electrode sheet and a sodium-ion battery, wherein polyacrylic acid is not added to the negative electrode slurry. The negative electrode slurry preparation process is adjusted as follows: hard carbon, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass ratio of 9.55:0.15:0.10:0.20, and then water is added to prepare a negative electrode slurry with a solid content of 10wt%, and the remaining conditions are the same as in Example 1.

[0052] Comparative Example 5 This comparative example provides an aluminum foil for a sodium-ion battery negative electrode, the preparation method of which is basically the same as that of Example 1, the only difference being the weight-average molecular weight (M) of the polyacrylic acid in the coating solution. w The number is adjusted to 500,000, and the other conditions are the same as in Example 1.

[0053] The comparative example also provides a sodium-ion battery negative electrode sheet and a sodium-ion battery, except that the aluminum foil used in this comparative example is the aluminum foil for the sodium-ion battery negative electrode, and the weight-average molecular weight (M) of polyacrylic acid is... w Except for the adjustment to 500,000, the other conditions are the same as in Example 1.

[0054] Comparative Example 6 This comparative example provides an aluminum foil for the negative electrode of a sodium-ion battery. Its preparation method is basically the same as that of Example 1, except that sodium oxalate in the coating solution is replaced with an equal mass of sodium carbonate, and the other conditions are the same as those of Example 1.

[0055] The comparative example also provides a sodium-ion battery negative electrode sheet and a sodium-ion battery, except that the aluminum foil used in the comparative example is the same as that in Example 1.

[0056] Performance testing The negative electrode sheets and sodium-ion batteries prepared in the above embodiments and comparative examples were subjected to performance tests, and the test methods are as follows: (1) Peel strength test: Using a tensile testing machine, peel the negative electrode material layer of the negative electrode sheet from the aluminum foil at a peel angle of 90° and a rate of (5.0±0.2) mm / s, and record the peel force value in N / m.

[0057] (2) Battery energy density test: At 25℃, the sodium-ion battery was charged at a constant current of 0.33C to the upper limit voltage, then charged at a constant voltage to the cutoff current of 0.05C, and then discharged at a constant current of 0.33C to the lower limit voltage. The discharge capacity was recorded and the battery energy density was calculated. Battery energy density (Wh / kg) = (discharge capacity × average discharge voltage) / battery mass.

[0058] (3) Cyclic performance test: At 25℃, the sodium-ion battery was charged at a constant current of 1C to the upper limit voltage of 3.45V, then charged at a constant voltage to the cutoff current of 0.05C, and then discharged at a constant current of 1C to the lower limit voltage of 1.5V. The rated capacity was set to 1C, and the initial capacity was recorded. The above 1C / 1C charge-discharge cycle was repeated for 1000 cycles, and the capacity retention rate was calculated. Capacity retention rate = (discharge capacity at 1000th cycle / initial discharge capacity) × 100%.

[0059] The performance test results of the sodium-ion batteries prepared in the examples and comparative examples are shown in Table 1.

[0060] Table 1. Performance test results of sodium-ion batteries prepared in the examples and comparative examples.

[0061] As can be seen from the test results in Table 1, in terms of peel strength, the peel strength of the negative electrodes in Examples 1-5 is significantly higher than that of the untreated battery negative electrode (Comparative Example 1), and also higher than that of Comparative Examples 2-6, where the pretreated coating composition is incomplete or replaced. This indicates that the synergistic effect of polyacrylic acid, polyvinylpyrrolidone, and sodium oxalate in this invention is crucial for improving the adhesion between the hard carbon coating and the aluminum foil.

[0062] Regarding energy density, the sodium-ion batteries in Examples 1-5 have energy densities of 98.3-102.4 Wh / kg, which are generally superior to those in Comparative Examples 1-6. This indicates that the addition of sodium oxalate is beneficial for the aluminum foil substrate to complete interface optimization and activation, thus strengthening the adhesion foundation; it can also provide effective sodium replenishment and improve the utilization rate of active sodium. Meanwhile, the additional addition of polyacrylic acid to the negative electrode slurry also makes a positive contribution to the energy density.

[0063] In terms of cycling performance, the retention rates after 1000 cycles in Examples 1-5 all exceeded 97%, which is superior to most comparative examples. This is attributed to the robust interfacial bonding and stable interfacial structure in the technical solution of this invention, which can effectively suppress electrode structure damage and interfacial side reactions during long-term cycling.

[0064] In summary, the aluminum foil provided by this invention, using sodium oxalate and polyacrylic acid in the pretreatment coating design, exhibits a synergistic effect, further enhancing adhesion and optimizing interface performance. Specifically, the coarsening and activation of the aluminum foil by sodium oxalate provides more chemical bonding sites and physical anchoring space for the polyacrylic acid, allowing it to interact more fully with the aluminum foil interface and improving overall bonding strength. Furthermore, the high molecular weight properties of polyacrylic acid can fill the microscopic gaps and unevenness created by etching on the aluminum foil surface, resulting in a tighter interface bond, reduced interface defects, and prevention of coating cracking caused by stress concentration. Meanwhile, the flexible three-dimensional network structure formed after polyacrylic acid curing can effectively buffer the volume expansion and contraction stress generated by hard carbon during the lithium insertion and extraction process, reduce the damage of volume deformation to the interface bonding, prevent the negative electrode layer from cracking, powdering and falling off, and maintain the structural integrity and interface adhesion of the electrode during long-term cycling. Moreover, the composite coating system is an aqueous system with excellent interfacial wettability with hard carbon and aluminum foil. After coating, it can form a uniform and continuous interface layer, avoiding the problems of local missing glue and uneven coating, and further ensuring the uniformity and stability of the adhesion.

[0065] Therefore, this invention effectively solves the problems of poor adhesion of negative electrode materials and insufficient battery energy density and cycle performance in the prior art through its unique aluminum foil surface pretreatment coating and its synergistic design with the negative electrode material layer, and has broad application prospects in the field of sodium-ion battery preparation.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various improvements and modifications without departing from the spirit and principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An aluminum foil for a sodium-ion battery negative electrode, characterized by, The surface of the aluminum foil is coated with a pretreatment coating; the pretreatment coating is formed by coating and drying a coating liquid; the coating liquid is composed of polyacrylic acid, polyvinylpyrrolidone, sodium oxalate and water; the mass ratio of polyacrylic acid, polyvinylpyrrolidone and sodium oxalate is (84~94):(3~8):(3~8).

2. The aluminum foil for the negative electrode of a sodium-ion battery according to claim 1, characterized in that, The solid content of the coating liquid is 2-8 wt%.

3. The aluminum foil for the negative electrode of a sodium-ion battery according to claim 1, characterized in that, The polyacrylic acid has a weight-average molecular weight of 800,000 to 1,200,000; the polyvinylpyrrolidone has a weight-average molecular weight of 40,000 to 80,000.

4. The aluminum foil for the negative electrode of a sodium-ion battery according to claim 1, characterized in that, The drying temperature is 80~140℃, and the time is 2~20min; the thickness of the pretreatment coating is 1~10μm.

5. A sodium-ion battery negative electrode sheet, characterized in that, It includes an aluminum foil for a sodium-ion battery negative electrode as described in any one of claims 1 to 4, and a negative electrode material layer coated on the aluminum foil.

6. The sodium-ion battery negative electrode sheet according to claim 5, characterized in that, The negative electrode material layer comprises the following components in the following mass ratio: 9.0-9.8 parts hard carbon, 0.1-0.4 parts conductive agent, 0.02-0.1 parts sodium carboxymethyl cellulose, 0.1-0.5 parts styrene-butadiene rubber, and 0.02-0.2 parts polyacrylic acid.

7. The sodium-ion battery negative electrode sheet according to claim 6, characterized in that, The conductive agent is selected from at least one of conductive graphite, conductive carbon black, carbon nanotubes, and acetylene black.

8. A sodium-ion battery, comprising a positive electrode, a separator, an electrolyte, and a negative electrode, characterized in that, The negative electrode is a sodium-ion battery negative electrode as described in any one of claims 5 to 7.

9. The sodium-ion battery according to claim 8, characterized in that, The positive electrode sheet includes a positive electrode material layer; the positive electrode material layer includes the following components in the following mass ratio: 9-9.8 parts of positive electrode active material, 0.05-0.5 parts of conductive agent, and 0.1-0.5 parts of polyvinylidene fluoride.

10. The sodium-ion battery according to claim 9, characterized in that, The positive electrode active material is selected from at least one of ternary positive electrode materials, polyanionic materials, and Prussian blue materials; the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and conductive graphite.

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