Modified current collectors, negative electrodes and sodium-ion batteries

Abstract

This invention provides a modified current collector, a negative electrode, and a sodium-ion battery, relating to the field of battery technology. The modified current collector provided by this invention includes an aluminum foil and an alumina layer, a fluorinated layer, and a carbon coating sequentially disposed on the surface of the aluminum foil; the fluorinated layer comprises a composite layer of NaF and AlF3; the carbon coating comprises a conductive carbon material, a binder, and a dispersant. The modified current collector provided by this invention can reduce the amount of negative electrode used, lower costs, and increase energy density, while avoiding fatal defects such as dendrites and interfacial instability in systems without a negative electrode, achieving a balance between performance and safety.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a modified current collector, a negative electrode, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries are considered a potential alternative to lithium-ion batteries due to abundant sodium resources, considerable cost-effectiveness, and similar operating principles. However, the peak energy density of sodium-ion batteries remains below 160 Wh / kg, significantly limiting their applicability in applications requiring higher energy densities. Electrodeless batteries utilize current collectors as the negative electrode to replace excess metallic sodium, eliminating the need for negative electrode active materials and significantly reducing the overall thickness and weight of the battery, thereby increasing its volumetric and gravimetric energy density. Furthermore, the electrodeless design reduces the presence of metallic sodium on the negative electrode, greatly reducing battery safety risks. However, electrodeless systems suffer from intractable technical drawbacks, including the high reactivity of metallic sodium deposited on the current collector, volume expansion during cycling, and dendrite formation.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The primary objective of this invention is to provide a modified current collector to solve the aforementioned technical problems.

[0005] The second objective of this invention is to provide a negative electrode.

[0006] A third objective of this invention is to provide a sodium-ion battery.

[0007] To achieve the above objectives, the following technical solution is adopted: In a first aspect, the present invention provides a modified current collector, comprising an aluminum foil and an aluminum oxide layer, a fluorinated layer and a carbon coating sequentially disposed on the surface of the aluminum foil; The fluorinated layer comprises a composite layer of NaF and AlF3; The carbon coating comprises conductive carbon material, binder, and dispersant.

[0008] As a further technical solution, the alumina layer is prepared by oxidizing aluminum foil.

[0009] As a further technical solution, the fluorinated layer is prepared by treating an aluminum foil with an alumina layer on its surface using a plasma device with a mixture of sodium and fluorine sources; The sodium source includes at least one of NaF, sodium formate, or sodium acetate; The fluorine source includes NF3.

[0010] As a further technical solution, the carbon coating is obtained by coating a slurry containing conductive carbon material, binder and dispersant.

[0011] As a further technical solution, the conductive carbon material includes at least one of conductive carbon black, conductive graphite, and carbon nanotubes; The adhesive includes at least one of PAA, PEO, CMC, or SBR; The dispersant includes at least one of PVP or PU; The mass ratio of the conductive carbon material, binder and dispersant is (90-95):(4-8):(1-2).

[0012] As a further technical solution, the thickness of the alumina layer is 10-30 nm; The thickness of the fluorinated layer is 5-15 nm; The thickness of the carbon coating is 1-5 μm.

[0013] Secondly, the present invention provides a negative electrode sheet, comprising the above-mentioned modified current collector and a negative electrode active material layer coated on the modified current collector.

[0014] As a further technical solution, the negative electrode active material layer includes hard carbon, a negative electrode conductive agent, and a negative electrode binder; The negative electrode conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene, conductive graphite, and carbon fiber. The negative electrode binder includes at least one of carboxymethyl cellulose, styrene-butadiene rubber and polyacrylic acid; In the negative electrode active material layer, the mass percentage of hard carbon is 94.5%-98%, the mass percentage of negative electrode conductive agent is 0.5%-2.0%, and the mass percentage of negative electrode binder is 1.5%-3.5%.

[0015] Thirdly, the present invention provides a sodium-ion battery, including the aforementioned negative electrode sheet.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The modified current collector provided by this invention can reduce the amount of negative electrode used, thereby lowering costs and increasing energy density. It can also avoid fatal defects such as dendrites and interface instability in a negative electrode-free system, achieving a balance between performance and safety. Detailed Implementation

[0017] The embodiments and examples of the present invention will be described in detail below. However, those skilled in the art will understand that the following embodiments and examples are for illustrative purposes only and should not be considered as limiting the scope of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise specified, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0018] In the cycling storage of a cathode-free sodium-ion battery, the rate of sodium ion diffusion from the electrolyte to the current collector and the nucleation sites determine the uniformity of sodium deposition. Simultaneously, the deposition of sodium ions and the generation of gas lead to significant volume expansion, which severely hinders the battery's application. The current collector, as a key component of the battery, determines the uniformity of the initial sodium deposition process and the stability of the cycling process through its structure and properties. Currently, the most common modification is simply coating a thin carbon layer onto the metal foil surface, which cannot promote uniform and stable sodium deposition, nor can it alleviate the volume expansion during cycling of the cathode-free sodium battery. Therefore, this invention proposes a technical solution.

[0019] In a first aspect, the present invention provides a modified current collector, comprising an aluminum foil and an aluminum oxide layer, a fluorinated layer and a carbon coating sequentially disposed on the surface of the aluminum foil; The fluorinated layer comprises a composite layer of NaF and AlF3; The carbon coating comprises conductive carbon material, binder, and dispersant.

[0020] This invention modifies and optimizes the performance of the current collector, enhancing its electron and ion conduction properties and improving its affinity for sodium ions. Finally, by coating it with a thin layer of hard carbon, it can reduce the amount of negative electrode used, lower costs, and increase energy density, while avoiding fatal defects such as dendrites and interface instability in a negative electrode-free system, thus achieving a balance between performance and safety.

[0021] In some alternative embodiments, the alumina layer is prepared by oxidizing aluminum foil.

[0022] In this invention, the alumina layer can uniformly transport ion channels, suppress local polarization and volume expansion, stabilize the interface structure, and reduce repeated SEI rupture and active material shedding.

[0023] In some alternative embodiments, the fluorinated layer is prepared by treating an aluminum foil with an alumina layer on its surface using a plasma device with a mixture of sodium and fluorine sources; The sodium source includes, but is not limited to, at least one of NaF, sodium formate, or sodium acetate; The fluorine source includes, but is not limited to, NF3.

[0024] The formed NaF-AlF3 composite phase can optimize ion transport channels, reduce interfacial polarization, enhance the bonding force between the oxide layer and the active material, and prevent material loss.

[0025] In some alternative embodiments, the carbon coating is obtained by coating a slurry containing conductive carbon material, a binder, and a dispersant.

[0026] Carbon coatings improve the peel strength and electronic conductivity of the coating, and reduce interfacial impedance.

[0027] In some optional embodiments, the conductive carbon material includes at least one of conductive carbon black, conductive graphite, and carbon nanotubes; The adhesive includes, but is not limited to, at least one of PAA, PEO, CMC or SBR; The dispersant includes, but is not limited to, at least one of PVP or PU; The mass ratio of the conductive carbon material, binder and dispersant is (90-95):(4-8):(1-2), for example, but not limited to 90:8:2, 95:4:1 or 93:5.5:1.5.

[0028] In some alternative embodiments, the thickness of the alumina layer is 10-30 nm, for example, but not limited to 10 nm, 20 nm or 30 nm; The thickness of the fluorinated layer is 5-15 nm, for example, but not limited to 5 nm, 10 nm or 15 nm; The thickness of the carbon coating is 1-5 μm, for example, but not limited to 1 μm, 3 μm or 5 μm.

[0029] Secondly, the present invention provides a negative electrode sheet, comprising the above-mentioned modified current collector and a negative electrode active material layer coated on the modified current collector.

[0030] The battery prepared using this negative electrode has high energy density and good safety.

[0031] In some alternative embodiments, the negative electrode active material layer includes hard carbon, a negative electrode conductive agent, and a negative electrode binder; The negative electrode conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene, conductive graphite, and carbon fiber. The negative electrode binder includes at least one of carboxymethyl cellulose, styrene-butadiene rubber and polyacrylic acid; In the negative electrode active material layer, the mass percentage of hard carbon is 94.5%-98%, for example, but not limited to 94.5%, 96% or 98%; The mass percentage of the negative electrode conductive agent is 0.5%-2.0%, for example, it can be, but is not limited to, 0.5%, 1.0% or 2.0%; The mass percentage of the negative electrode binder is 1.5%-3.5%, for example, it can be, but is not limited to, 1.5%, 2% or 3.5%.

[0032] Thirdly, the present invention provides a sodium-ion battery, including the aforementioned negative electrode sheet.

[0033] This sodium-ion battery has high energy density and good safety.

[0034] The present invention will be further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0035] Example 1 A modified current collector includes an aluminum foil and an aluminum oxide layer, a fluorinated layer, and a carbon coating sequentially disposed on the surface of the aluminum foil.

[0036] The preparation method is as follows: (1) Fast ion conductor layer (alumina layer): The natural oxide layer (Al2O3) on the surface of aluminum foil has uneven thickness, loose and porous structure, and poor ionic conductivity, which will hinder Na + The transfer process induces an increase in interfacial impedance. A dense oxide layer is generated on the surface through degreasing, pickling, and controlled oxidation treatment. The main components of the oxide layer are γ-Al2O3 and amorphous Al2O3, thus obtaining current collector-A.

[0037] (2) Fluoride layer: The above current collector-A is cleaned with argon plasma for 20-30 s to remove surface oil and loose oxide layer, and expose the active sites on the surface of dense oxide layer. Ar / NaF / NF3 mixed gas (volume ratio NaF:NF3:Ar=1:1-3:20-25) is introduced with a power of 500-1500W, a processing time of 10-30s, and a temperature of ≤100℃ to avoid high temperature damage to oxide layer structure. Finally, it is purged with inert gas to remove residual fluoride and sodium source, forming a uniform composite fluoride layer to obtain current collector-B.

[0038] (3) Carbon coating: Conductive graphite, binder (PAA) and dispersant (PVP) in a mass ratio of (90:8:2) are placed in deionized water and stirred to form a slurry with a solid content of 10%-15%. After being dispersed in a sand mill and further stirred, an aqueous slurry with a solid content of 9%-12% and a viscosity of 80-120 is formed. The above slurry is coated on the surface of current collector-B by a gravure screen roller. After drying, modified current collector-C is obtained, which is the modified current collector of the present invention (the current collector has an alumina layer thickness of 20nm, a fluorinated layer thickness of 10nm, and a carbon coating thickness of 1um).

[0039] Example 2 A modified current collector differs from Example 1 in that the oxide layer thickness is 10 nm, the fluorinated layer thickness is 5 nm, the carbon coating thickness is 5 μm, and the conductive agent of the carbon coating is carbon nanotubes.

[0040] Example 3 A modified current collector differs from Example 1 in that the oxide layer thickness is 30 nm, the fluorinated layer thickness is 15 nm, the carbon coating thickness is 3 μm, and the conductive agent of the carbon coating is conductive carbon black.

[0041] Comparative Example 1 A current collector, which differs from Example 1 in that it does not contain an alumina layer.

[0042] Comparative Example 2 A current collector, which differs from Example 1 in that it does not contain a fluorinated layer.

[0043] Comparative Example 3 A current collector differs from Example 1 in that no sodium source is introduced during the preparation of the fluorinated layer.

[0044] Comparative Example 4 A current collector, which differs from Example 1 in that it does not contain a carbon coating.

[0045] Comparative Example 5 A current collector, which differs from Example 1 in that it does not contain an alumina layer and a fluoride layer.

[0046] Experimental Example 1 The current collectors provided in the above embodiments and comparative examples are used to prepare negative electrode sheets, which are then stacked in a Z-shape with positive electrode sheets, separators, and electrolytes to form a battery. The specific steps are as follows: (1) Preparation of positive electrode sheet: The positive electrode material, binder, dispersant, and conductive agent (positive electrode material - NFPP / layered oxide / Prussian blue white 94.5-97.7%, positive electrode conductive agent - conductive carbon black / conductive graphite / carbon nanotube 1.5-2.5%, dispersant - PVP 0.3-0.5%, and positive electrode binder - PVDF 0.5-2.5%) are added to N-methylpyrrolidone (NMP) in proportion, stirred evenly, and a slurry is prepared. The output solid content is 50-60%, and the viscosity is 7000-8000. Then, the slurry is coated on a coating machine by extrusion or transfer. The double-sided areal density of the positive electrode sheet is controlled to be 30-39 mg / cm³. 2 After rolling and punching, the corresponding electrode sheets are produced, with the thickness of the positive electrode sheet ranging from 170 to 191 μm.

[0047] (2) Preparation of negative electrode sheet: Hard carbon, conductive agent, and binder are added to deionized water in the following proportions (negative electrode active material - hard carbon 94.5-98%, negative electrode conductive agent - conductive carbon black / graphite / carbon nanotube 0.5-2.0%, negative electrode binder - PAA / SBR / CMC 1.5-3.5%), stirred evenly, and a slurry is prepared. The solid content of the slurry is 40%-55%, and the viscosity is 4000-6000. It is coated onto the surface of the modified current collector-C by extrusion or transfer. The double-sided areal density of the negative electrode is controlled at 4.3-6.8 mg / cm³. 2 After rolling and punching, the corresponding electrode sheets are produced, with the thickness of the negative electrode sheets ranging from 61 to 75 μm.

[0048] (3) Electrolyte preparation: Sodium salt (14-16% sodium salt such as NaPF6, NaBF4, NaClO4, etc.), additives (0.1-1.0% such as VC, FEC, PS, etc.), solvent (DME, DEGDME, THF, TEGDME, DOL, etc., the rest are all solvents) are mixed evenly in proportion to prepare electrolyte.

[0049] (4) Battery preparation: The positive electrode / separator / negative electrode are stacked to form a battery.

[0050] The sodium-ion batteries prepared using the various embodiments and comparative examples were tested for their initial coulombic efficiency and cycle performance. The specific test methods are as follows: First Coulomb efficiency test of the battery: After the assembled battery was left to stand for 10 hours, it was charged to 3.5V at a constant current and constant voltage of 0.2C, then left to stand for another 0.5 hours, and then discharged to 2.0V at a constant current of 0.5C. The ratio of the battery's discharge capacity to its charge capacity was calculated as CE. Cycle life test: After the assembled battery is left to rest for 10 hours, it is charged to 3.5V at 0.5C constant current and constant voltage at room temperature of 25℃. After resting for 0.5 hours, it is discharged to 2.0V at 1C constant current. The cycle is repeated 100 times and the capacity retention rate is recorded. Volume change test: After the battery has undergone capacity formation, it is placed at room temperature (25℃) for 10 hours. The initial volume of the battery is measured by the water displacement method and recorded as V1. Then, it is placed in a high-temperature chamber at 45℃ for 7 days. After being removed and cooled to room temperature (25℃), the volume after storage is measured by the water displacement method and recorded as V2. The volume change rate after 7 days of storage at 45℃ is ΔV = (V2 - V1) / V1. 100%.

[0051] The performance of the obtained batteries was tested, and the results are as follows:

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified current collector, characterized in that, It includes aluminum foil and an aluminum oxide layer, a fluorinated layer and a carbon coating sequentially disposed on the surface of the aluminum foil; The fluorinated layer comprises a composite layer of NaF and AlF3; The carbon coating comprises conductive carbon material, binder, and dispersant.

2. The modified current collector according to claim 1, characterized in that, The alumina layer is prepared by oxidizing aluminum foil.

3. The modified current collector according to claim 1, characterized in that, The fluorinated layer is prepared by treating an aluminum foil with an aluminum oxide layer on its surface using a plasma device with a mixture of sodium and fluorine sources. The sodium source includes at least one of NaF, sodium formate, or sodium acetate; The fluorine source includes NF3.

4. The modified current collector according to claim 1, characterized in that, The carbon coating is obtained by applying a slurry containing conductive carbon material, binder and dispersant.

5. The modified current collector according to claim 1, characterized in that, The conductive carbon material includes at least one of conductive carbon black, conductive graphite, and carbon nanotubes. The adhesive includes at least one of PAA, PEO, CMC, or SBR; The dispersant includes at least one of PVP or PU; The mass ratio of the conductive carbon material, binder and dispersant is (90-95):(4-8):(1-2).

6. The modified current collector according to claim 1, characterized in that, The thickness of the alumina layer is 10-30 nm; The thickness of the fluorinated layer is 5-15 nm; The thickness of the carbon coating is 1-5 μm.

7. A negative electrode sheet, characterized in that, It includes the modified current collector as described in any one of claims 1-6 and the negative electrode active material layer coated on the modified current collector.

8. The negative electrode sheet according to claim 7, characterized in that, The negative electrode active material layer includes hard carbon, a negative electrode conductive agent, and a negative electrode binder; The negative electrode conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene, conductive graphite, and carbon fiber. The negative electrode binder includes at least one of carboxymethyl cellulose, styrene-butadiene rubber and polyacrylic acid; In the negative electrode active material layer, the mass percentage of hard carbon is 94.5%-98%, the mass percentage of negative electrode conductive agent is 0.5%-2.0%, and the mass percentage of negative electrode binder is 1.5%-3.5%.

9. A sodium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 7 or 8.

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