Foil without negative electrode coating as well as preparation method and application of foil

Abstract

The invention provides a foil without a negative electrode coating as well as a preparation method and application thereof, and relates to the technical field of batteries. The invention provides a foil without a negative electrode coating. The foil comprises a current collector, a lower coating and an upper coating, wherein the current collector is sequentially coated with the lower coating and the upper coating; the lower-layer coating is prepared by coating the slurry of the lower-layer coating and then heating to decompose sodium bicarbonate into sodium carbonate; the slurry of the lower coating comprises a carbon nanotube, a conductive agent, a binder, sodium bicarbonate and a solvent; the upper-layer coating is obtained by coating slurry of the upper-layer coating; the slurry of the upper coating comprises a carbon nanotube, a conductive agent, a binder, sodium dihydrogen phosphate and a solvent. The non-cathode coating foil has good stability, is used for a non-cathode sodium ion battery, and can effectively improve the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a foil without a negative electrode coating, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries have become a research hotspot in the energy storage field due to their abundant resources and low cost. Among existing technologies, anode-less sodium-ion batteries, which directly use metallic sodium foil as the anode, offer advantages such as simplified structure, significantly reduced cost, increased energy density, and environmental friendliness. They hold particularly promising application prospects for energy storage systems built upon the abundant sodium element. However, this technology currently faces three major challenges: sodium dendrite growth, dead sodium formation, and an unstable SEI layer. These issues lead to short battery cycle life and low coulombic efficiency. To address these problems, further refining the preparation of the anode coating is crucial.

[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 foil material without a negative electrode coating to solve the aforementioned technical problems.

[0005] The second objective of this invention is to provide a method for preparing the above-mentioned foil without a negative electrode coating.

[0006] A third objective of this invention is to provide the application of the above-mentioned electrodeless coating foil in electrodeless sodium-ion batteries.

[0007] To achieve the above objectives, the following technical solution is adopted: In a first aspect, the present invention provides a foil material without a negative electrode coating, comprising a current collector and a lower coating and an upper coating sequentially coated on the current collector; The lower coating layer is prepared by applying a slurry of the lower coating layer and then heating it to decompose sodium bicarbonate into sodium carbonate. The slurry of the lower coating layer includes carbon nanotubes (CNTs), a conductive agent, a binder, sodium bicarbonate, and a solvent, wherein the mass ratio of the carbon nanotubes, conductive agent, binder, and sodium bicarbonate is (92-91):(5-2):(1-2):(2-5). The upper coating layer is obtained by applying a slurry for the upper coating layer; The slurry of the upper coating layer includes carbon nanotubes, conductive agent, binder, sodium dihydrogen phosphate and solvent, and the mass ratio of carbon nanotubes, conductive agent, binder and sodium dihydrogen phosphate is (92-91):(5-2):(1-2):(2-5).

[0008] As a further technical solution, the current collector includes aluminum foil or copper foil.

[0009] As a further technical solution, the conductive agent in the slurry of the lower coating includes SP (conductive carbon black), the binder includes SBR (styrene-butadiene rubber) or PAA (polyacrylic acid), and the solvent includes water.

[0010] As a further technical solution, the viscosity of the adhesive in the lower coating layer is 200-1500 mPa·s, and the solid content is 5wt%-20wt%.

[0011] As a further technical solution, the coating thickness of the slurry in the lower coating layer is 10-14 μm.

[0012] As a further technical solution, the conductive agent in the slurry of the upper coating includes SP, the binder includes SBR or PAA, and the solvent includes water.

[0013] As a further technical solution, the viscosity of the adhesive in the upper coating is 200-1500 mPa·s, and the solid content is 5wt%-20wt%.

[0014] As a further technical solution, the coating thickness of the upper coating slurry is 4-6 μm.

[0015] Secondly, the present invention provides a method for preparing the above-mentioned foil without a negative electrode coating, comprising the following steps: A slurry for coating the lower layer is coated onto a current collector. After heating, sodium bicarbonate is decomposed into sodium carbonate to form the lower layer coating. Then, a slurry for coating the upper layer coating is coated onto the lower layer coating to form the upper layer coating, thus preparing a foil without a negative electrode coating.

[0016] Thirdly, the present invention provides the application of the above-mentioned electrodeless coating foil in electrodeless sodium-ion batteries.

[0017] Compared with the prior art, the non-negative electrode coated foil provided by the present invention has the following beneficial effects: 1. The upper coating uses sodium dihydrogen phosphate and CNTs to construct a dense coating to improve the contact between the negative electrode side and the separator; the lower coating material uses carbon nanotubes and sodium bicarbonate to construct a three-dimensional structure. After sodium bicarbonate is heated to form sodium carbonate and carbon dioxide, the gas evolution will form physical pore channels, which, together with carbon nanotubes, further improve the physical diffusion rate of sodium ions. Sodium carbonate particles act as sites to prevent carbon nanotubes from forming a parallel stacked structure in the coating, which can accommodate more sodium ions dispersed in the coating structure, improve sodium loss and side reaction gas generation caused by sodium ion enrichment between the negative electrode coating and the separator during the cycle process; 2. The synergistic effect of the sodium carbonate and sodium dihydrogen phosphate dual coatings: The upper layer of sodium dihydrogen phosphate undergoes a reduction reaction on the surface of the negative electrode coating to form glassy sodium metaphosphate. This protective layer is dense and uniform, effectively isolating the electrolyte from the negative electrode side. Furthermore, this substance exhibits excellent sodium ion migration rate, promoting interfacial transport of sodium ions. In addition, the P=O bond can attack the H atoms of hydrofluoric acid, thereby consuming some of the free hydrofluoric acid. The lower layer of sodium carbonate and other components also form a stable inorganic salt-based SEI film, reducing sodium ion loss. Sodium carbonate has excellent heat resistance within the battery, remains stable during battery cycling, and is suitable for high-temperature operating environments. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is the result of test example 1 of the present invention. Detailed Implementation

[0020] 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.

[0021] In a first aspect, the present invention provides a foil material without a negative electrode coating, comprising a current collector and a lower coating and an upper coating sequentially coated on the current collector; The lower coating layer is prepared by applying a slurry of the lower coating layer and then heating it to decompose sodium bicarbonate into sodium carbonate. The slurry of the lower coating layer includes carbon nanotubes, conductive agent, binder, sodium bicarbonate and solvent. The mass ratio of the carbon nanotubes, conductive agent, binder and sodium bicarbonate can be, for example, but not limited to, 92:5:1:2, 91:2:2:5 or 91.5:3:1.5:4. The upper coating layer is obtained by applying a slurry for the upper coating layer; The slurry of the upper coating layer includes carbon nanotubes, a conductive agent, a binder, sodium dihydrogen phosphate, and a solvent. The mass ratio of the carbon nanotubes, conductive agent, binder, and sodium dihydrogen phosphate can be, for example, but is not limited to, 92:5:1:2, 91:2:2:5, or 91.5:3:1.5:4.

[0022] The electrodeless coating foil provided by this invention has good stability and can be used in the preparation of electrodeless sodium-ion batteries.

[0023] In some alternative embodiments, the current collector is an aluminum foil or a copper foil.

[0024] In some alternative embodiments, the conductive agent in the slurry of the lower coating includes, but is not limited to, SP; the binder includes, but is not limited to, SBR or PAA; and the solvent includes, but is not limited to, water.

[0025] In some optional embodiments, the viscosity of the adhesive of the lower coating layer may be, but is not limited to, 200 mPa·s, 1000 mPa·s or 1500 mPa·s, and the solid content may be, but is not limited to, 5 wt%, 10 wt% or 20 wt%.

[0026] In some optional embodiments, the coating thickness of the slurry of the lower coating layer may be, but is not limited to, 10 μm, 12 μm or 14 μm.

[0027] In some alternative embodiments, the conductive agent in the slurry of the upper coating includes, but is not limited to, SP; the binder includes, but is not limited to, SBR or PAA; and the solvent includes, but is not limited to, water.

[0028] In some optional embodiments, the viscosity of the adhesive of the upper coating may be, but is not limited to, 200 mPa·s, 1000 mPa·s or 1500 mPa·s, and the solid content may be, but is not limited to, 5 wt%, 10 wt% or 20 wt%.

[0029] In some optional embodiments, the coating thickness of the upper coating slurry can be, but is not limited to, 4μm, 5μm or 6μm.

[0030] Secondly, the present invention provides a method for preparing the above-mentioned foil without a negative electrode coating, comprising the following steps: A slurry for coating the lower layer is coated onto a current collector. After heating, sodium bicarbonate is decomposed into sodium carbonate to form the lower layer coating. Then, a slurry for coating the upper layer coating is coated onto the lower layer coating to form the upper layer coating, thus preparing a foil without a negative electrode coating.

[0031] The preparation method is simple and convenient.

[0032] In some alternative implementations, the dispersion of carbon nanotubes is promoted by ultrasound or by adding polyvinylpyrrolidone to the solution.

[0033] Thirdly, the present invention provides the application of the above-mentioned electrodeless coating foil in electrodeless sodium-ion batteries.

[0034] The present invention will be further illustrated below with specific embodiments. 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 foil without a negative electrode coating is prepared by the following method: 1. Carbon nanotubes are added to water and initially dispersed by ultrasonic treatment to remove agglomeration and improve dispersibility; 2. Dissolve polyvinylpyrrolidone powder in water to form a homogeneous solution with a concentration of 0.1%-1% by mass; 3. Slowly add the pretreated CNT dispersion to the polyvinylpyrrolidone solution while stirring for 30 minutes to ensure thorough mixing; 4. Further disperse CNTs by ultrasonic treatment. The interaction between the amide groups of polyvinylpyrrolidone and the CNT surface is utilized to prevent agglomeration. The ultrasonic power is 100-140W and the time is 60-80 minutes to avoid over-treatment that may cause structural damage. 5. Prepare a slurry by adding water to the solution from step 4 in a mass ratio of CNT: conductive agent SP: binder PAA: sodium bicarbonate of 92: 5: 1: 2. The slurry viscosity is 200 mPa·s and the solid content is 5%. Coat the slurry onto aluminum foil with a coating thickness of 10 μm. Then, bake the coating in a high-temperature oven at 150°C to decompose the sodium bicarbonate and produce sodium carbonate. 6. Prepare a slurry by adding water to the solution from step 4 in a mass ratio of CNT: conductive agent SP: binder PAA: sodium dihydrogen phosphate of 92: 5: 1: 2. The slurry viscosity is 200 mPa·s and the solid content is 5%. Coat the slurry onto the coating from step 5 to a thickness of 4 μm. Example 2 A foil without a negative electrode coating is prepared by the following method: 1. Carbon nanotubes are added to water and initially dispersed by ultrasonic treatment to remove agglomeration and improve dispersibility; 2. Dissolve polyvinylpyrrolidone powder in water to form a homogeneous solution with a concentration of 0.1%-1% by mass; 3. Slowly add the pretreated CNT dispersion to the polyvinylpyrrolidone solution while stirring for 30 minutes to ensure thorough mixing; 4. Further disperse CNTs by ultrasonic treatment. The interaction between the amide groups of polyvinylpyrrolidone and the CNT surface is utilized to prevent agglomeration. The ultrasonic power is 100-140W and the time is 60-80 minutes to avoid over-treatment that may cause structural damage. 5. Prepare a slurry by adding water to the solution from step 4 in a mass ratio of CNT: conductive agent SP: binder PAA: sodium bicarbonate of 91:2:2:5. The slurry has a viscosity of 1500 mPa·s and a solid content of 20%. Coat the slurry onto aluminum foil to a thickness of 14 μm. 6. Prepare a slurry by adding water to the solution from step 4 in a mass ratio of CNT: conductive agent SP: binder PAA: sodium dihydrogen phosphate of 91:2:2:5. The slurry has a viscosity of 1500 mPa·s and a solid content of 20%. Coat the slurry onto the coating from step 5 to a thickness of 6 μm. Example 3 A foil without a negative electrode coating is prepared by the following method: 1. Carbon nanotubes are added to water and initially dispersed by ultrasonic treatment to remove agglomeration and improve dispersibility; 2. Dissolve polyvinylpyrrolidone powder in water to form a homogeneous solution with a concentration of 0.1%-1% by mass; 3. Slowly add the pretreated CNT dispersion to the polyvinylpyrrolidone solution while stirring for 30 minutes to ensure thorough mixing; 4. Further disperse CNTs by ultrasonic treatment. The interaction between the amide groups of polyvinylpyrrolidone and the CNT surface is utilized to prevent agglomeration. The ultrasonic power is 100-140W and the time is 60-80 minutes to avoid over-treatment that may cause structural damage. 5. Prepare a slurry by adding water to the solution from step 4 in a mass ratio of CNT: conductive agent SP: binder PAA: sodium bicarbonate of 91.5:3:1.5:4. The slurry viscosity is 1000 mPa·s and the solid content is 10%. Coat the slurry onto aluminum foil to a thickness of 12 μm. 6. Prepare a slurry by adding water to the solution from step 4 according to the mass ratio of CNT: conductive agent SP: binder PAA: sodium dihydrogen phosphate in 91.5: 3:1.5:4. The slurry viscosity is 1000 mPa·s and the solid content is 10%. Coat the slurry onto the coating from step 5 to a thickness of 5 μm. Comparative Example 1 A foil without a negative electrode coating, which differs from Example 1 in that sodium bicarbonate is replaced with 0.5 times the molar amount of sodium carbonate.

[0036] Comparative Example 2 A foil without a negative electrode coating differs from Example 1 in that it does not have a lower coating layer.

[0037] Comparative Example 3 A foil without a negative electrode coating, which differs from Example 1 in that it does not have an upper coating layer.

[0038] Comparative Example 4 A hard carbon anode material coating differs from Example 1 in that the coating material is biomass hard carbon.

[0039] Experimental Example 1 The negative electrode-free coated foils provided in Examples 1-3 and Comparative Examples 1-4 were assembled with PP separators, positive electrode sheets, and electrolytes to form negative electrode-free sodium-ion batteries. The positive electrode sheet was formulated with NFPP (composite sodium iron phosphate):PVDF (polyvinylidene fluoride):SP:CNT:dispersant CMC in a ratio of 95:1.5:1.5:1.5:0.5. The coated foil was aluminum foil, and the electrolyte was diethylene glycol dimethyl ether containing 1 mol / L NaPF6.

[0040] The batteries were subjected to charge-discharge cycle tests (25°C, 0.5C charging, 1C discharging), and the results are as follows. Figure 1 As shown. From Figure 1 The results show that the battery prepared from the negative electrode-free foil provided in this application has better cycle performance.

[0041] 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 foil material without a negative electrode coating, characterized in that, It includes a current collector and a lower coating and an upper coating sequentially coated on the current collector; The lower coating layer is prepared by applying a slurry of the lower coating layer and then heating it to decompose sodium bicarbonate into sodium carbonate. The slurry of the lower coating layer includes carbon nanotubes, conductive agent, binder, sodium bicarbonate and solvent, and the mass ratio of carbon nanotubes, conductive agent, binder and sodium bicarbonate is (92-91):(5-2):(1-2):(2-5). The upper coating layer is obtained by applying a slurry for the upper coating layer; The slurry of the upper coating layer includes carbon nanotubes, conductive agent, binder, sodium dihydrogen phosphate and solvent, and the mass ratio of carbon nanotubes, conductive agent, binder and sodium dihydrogen phosphate is (92-91):(5-2):(1-2):(2-5).

2. The foil material without a negative electrode coating according to claim 1, characterized in that, The current collector includes aluminum foil or copper foil.

3. The foil material without a negative electrode coating according to claim 1, characterized in that, The conductive agent in the slurry of the lower coating layer includes SP, the binder includes SBR or PAA, and the solvent includes water.

4. The foil material without a negative electrode coating according to claim 1, characterized in that, The viscosity of the adhesive in the lower coating layer is 200-1500 mPa·s, and the solid content is 5wt%-20wt%.

5. The foil material without a negative electrode coating according to claim 1, characterized in that, The coating thickness of the slurry in the lower coating layer is 10-14 μm.

6. The foil without negative electrode coating according to claim 1, characterized in that, The conductive agent in the slurry of the upper coating includes SP, the binder includes SBR or PAA, and the solvent includes water.

7. The foil material without a negative electrode coating according to claim 1, characterized in that, The viscosity of the adhesive in the upper coating is 200-1500 mPa·s, and the solid content is 5wt%-20wt%.

8. The foil material without a negative electrode coating according to claim 1, characterized in that, The coating thickness of the upper coating slurry is 4-6 μm.

9. The method for preparing the non-anode coated foil according to any one of claims 1-8, characterized in that, Includes the following steps: A slurry for coating the lower layer is coated onto a current collector. After heating, sodium bicarbonate is decomposed into sodium carbonate to form the lower layer coating. Then, a slurry for coating the upper layer coating is coated onto the lower layer coating to form the upper layer coating, thus preparing a foil without a negative electrode coating.

10. The application of the electrodeless coating foil according to any one of claims 1-8 in an electrodeless sodium-ion battery.

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