Sodium-ion secondary battery positive electrode slurry and preparation method thereof

Abstract

The present application relates to a kind of sodium ion secondary batteries, specifically to a kind of sodium ion secondary battery positive pole slurry and preparation method thereof.Sodium ion secondary battery positive pole slurry includes: sodium ion positive pole material, conductive agent, binder composition, dispersing agent, the binder composition includes polyacrylonitrile and polyvinylidene fluoride.In the present application sodium ion secondary battery positive pole slurry, there is alkali-resistant binder and dispersing agent, at least can effectively prevent slurry jelly in the process of preparation and coating process, the existence of scratch problem in coating process.

Description

Technical Field

[0001] This invention relates to sodium-ion secondary batteries, specifically to a positive electrode slurry for sodium-ion secondary batteries and its preparation method. Background Technology

[0002] Sodium is widely available and abundant, and its price is far lower than that of lithium. In recent years, with the soaring price of lithium, sodium-ion batteries have attracted widespread attention due to their potential cost reduction of 30-50% compared to lithium-ion batteries, especially in energy storage, hybrid power, and lead-acid battery replacement, where they show promising application prospects.

[0003] Currently, the most mature sodium-ion cathode materials are sodium iron-nickel-manganese oxide, sodium vanadium phosphate, and Prussian white. During the preparation of these sodium-ion battery cathode materials, an excess of sodium (Na) is added to obtain a cathode material with good crystallinity. Therefore, sodium-ion cathode materials always have a small amount of residual Na (existing as Na₂O at high temperatures). When the temperature drops to room temperature, Na₂O adsorbs CO₂ and H₂O from the air to form NaOH and Na₂CO₃, making the cathode material alkaline. Furthermore, Na is more alkaline than Li, therefore, the alkalinity of sodium-ion cathode materials is much higher than that of lithium-ion cathode materials.

[0004] Because the surface pH of sodium ion cathode materials is too high, usually >13, they are extremely prone to absorbing moisture during the cathode slurry preparation process. The Na2O on the material surface reacts with CO2 and H2O in the air to form NaOH and Na2CO3, etc. The free alkali attacks the CF / CH bonds on the binder, causing the binder to lose HF and form double bonds, resulting in cross-linking and ultimately forming a jelly-like state. The jelly-like slurry is difficult to sieve due to powder agglomeration. Even if the jelly-like slurry can be sieved, micro-agglomerates will still exist after sieving. During the coating process, defects such as electrode scratches will occur intermittently, resulting in a low preparation and processing qualification rate. Furthermore, the subsequent electrode will also absorb moisture from the air. These sodium residues will deteriorate the electrochemical environment of the battery, promote electrolyte decomposition, and reduce battery performance. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the prior art.

[0006] This invention provides a sodium-ion secondary battery positive electrode slurry and its preparation method. The slurry contains an alkali-resistant binder and a dispersant, which can at least effectively prevent the slurry from becoming jelly-like during preparation and coating, and prevent scratches during coating.

[0007] The inventors discovered that polyacrylonitrile, an alkali-resistant binder in the positive electrode slurry of sodium-ion secondary batteries, does not undergo a de-HF reaction similar to that of polyvinylidene fluoride (PVDF) in the presence of NaOH and Na2CO3, which leads to double bond formation, cross-linking, and ultimately a jelly-like state. However, if the binder in the slurry is only polyacrylonitrile, the resulting electrode is brittle, and the compaction density of the electrode is reduced. Therefore, it needs to be used in combination with a certain amount of PVDF.

[0008] The present invention first provides a binder composition for positive electrode slurry of sodium-ion secondary battery, comprising polyacrylonitrile and polyvinylidene fluoride in a mass ratio of (1-8):(2-9).

[0009] In some embodiments of the present invention, the mass ratio of polyacrylonitrile to polyvinylidene fluoride in the adhesive composition is 1:(1-2). In some specific examples, the mass ratio of polyacrylonitrile to polyvinylidene fluoride is 1:1, 1:2, 1:9, 8:2, or 8:9.

[0010] In some embodiments of the present invention, the adhesive composition is composed of polyacrylonitrile and polyvinylidene fluoride, that is, a compound of the two.

[0011] The present invention also provides the application of the above-described binder composition in the preparation of sodium-ion secondary battery positive electrode slurry. Optionally, the content of the binder composition in the sodium-ion secondary battery positive electrode slurry is 1-4 wt%.

[0012] The present invention also provides a sodium-ion secondary battery positive electrode slurry, comprising: sodium-ion positive electrode material, conductive agent, the above-mentioned binder composition, and dispersant.

[0013] According to an embodiment of the present invention, in the sodium-ion secondary battery positive electrode slurry, the mass ratio of sodium-ion positive electrode material, conductive agent, binder composition and dispersant is (90-96):(1-5):(1-4):(0.1-1). Alternatively, it can be (94-95.5):(1.5-3):(2.5-2.8):(0.2-0.5).

[0014] According to embodiments of the present invention, the sodium ion cathode material may be selected from one or more of sodium iron-nickel manganese oxide, sodium vanadium phosphate, Prussian white, and sodium vanadium fluorophosphate.

[0015] According to embodiments of the present invention, the conductive agent is selected from one or more of acetylene black, carbon black, carbon nanotubes, and graphene.

[0016] According to an embodiment of the present invention, the dispersant is sodium polyaspartate (PASP).

[0017] The dispersant used in this invention can effectively improve the surface properties of sodium ion cathode materials, reduce the surface energy of particles, increase the affinity with the dispersion medium, and effectively inhibit particle aggregation, thereby increasing dispersion performance. At the same time, it can inhibit the segregation of polyacrylonitrile and polyvinylidene fluoride in the coating and drying process, thereby improving the cycle performance of the battery.

[0018] According to an embodiment of the present invention, the sodium-ion secondary battery positive electrode slurry further includes N-methylpyrrolidone (NMP).

[0019] According to an embodiment of the present invention, in the sodium-ion secondary battery positive electrode slurry, the mass ratio of N-methylpyrrolidone to the sum of the masses of sodium-ion positive electrode material, conductive agent, binder composition and dispersant is (0.1-1):1, optionally (0.4-0.8):1.

[0020] The present invention also provides a method for preparing the above-mentioned sodium-ion secondary battery positive electrode slurry, comprising: mixing N-methylpyrrolidone with the binder composition and dispersant to form a slurry; mixing the slurry with a conductive agent to form a conductive slurry; and then adding sodium-ion positive electrode material and mixing.

[0021] In some specific examples, the preparation method of the above-mentioned sodium-ion secondary battery positive electrode slurry includes:

[0022] 1) Take sodium ion positive electrode material, conductive agent, binder, and dispersant according to the specified ratio;

[0023] 2) First, add NMP to the dual-paddle dual-dispersion equipment, then add the binder composition and dispersant in sequence. The stirring speed is 10-40 r / min, the dispersion disc linear speed is 20-60 m / s, and the running time is 60-150 min to form a colloid. Then add the conductive agent. The stirring speed is 10-40 r / min, the dispersion disc linear speed is 20-60 m / s, and the running time is 30-90 min to form a conductive colloid. Then add the sodium ion positive electrode material (for example, add it evenly in three parts). The stirring speed is 10-40 r / min, the dispersion disc linear speed is 15-50 m / s, and the running time is 30-60 min to form a slurry.

[0024] In some embodiments, the prepared slurry has a solid content of 50-76.9%, and the slurry has low fineness, good sieving performance, and does not jelly within 24 hours.

[0025] The positive electrode slurry prepared by this invention has a solid content that is 5-10% higher than that prepared by traditional methods. The slurry has lower fineness, better sieving performance, and does not jelly within 24 hours.

[0026] In this invention, the alkali-resistant binder polyacrylonitrile in the sodium-ion secondary battery cathode slurry does not undergo a double bond formation reaction similar to that of PVDF in the presence of NaOH and Na2CO3, resulting in cross-linking and ultimately a jelly-like state. The dispersant sodium polyaspartate (PASP) effectively improves the surface properties of the sodium-ion cathode material, reduces the surface energy of the particles, increases the affinity with the dispersion medium, and effectively inhibits particle aggregation, thereby increasing dispersion performance. Simultaneously, it can suppress the segregation of polyacrylonitrile and PVDF during the coating and drying process, improving the battery's cycle performance.

[0027] The present invention also provides the application of the above-mentioned sodium-ion secondary battery positive electrode slurry in the preparation of sodium-ion secondary batteries.

[0028] The present invention also provides a positive electrode sheet for a sodium-ion secondary battery, comprising the above-mentioned sodium-ion secondary battery positive electrode slurry. In some examples, the positive electrode slurry is coated on a 15-micron aluminum foil, dried at 95°C, and then rolled to obtain the positive electrode sheet.

[0029] The present invention also provides a sodium-ion secondary battery, comprising the above-mentioned positive electrode sheet or comprising the above-mentioned sodium-ion secondary battery positive electrode slurry. Detailed Implementation

[0030] The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the examples, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased from legitimate channels.

[0031] Example 1

[0032] This embodiment provides a sodium-ion secondary battery positive electrode slurry, and the preparation method is as follows:

[0033] 1) Weigh sodium iron-nickel-manganese oxide, conductive agent, binder, and dispersant according to the following mass ratio: The mass ratio of the above four substances is 95.5:1.5:2.5:0.5; the conductive agent is acetylene black; the binder is PVDF and polyacrylonitrile with a mass ratio of 2:1; the dispersant is sodium polyaspartate; the total weight of the powder is 500 kg.

[0034] 2) Weigh NMP and add it to a 600L dual-paddle dual-dispersion apparatus. The mass ratio of NMP to the total mass of all substances in step 1 is 0.4.

[0035] 3) Preparation of adhesive solution: Add the binder polyacrylonitrile, binder PVDF and dispersant to NMP in step 2 in sequence. The stirring speed is 26 r / min, the dispersion disc linear velocity is 36 m / s, and the running time is 120 min.

[0036] 4) Preparation of conductive adhesive: Add conductive agent acetylene black to the adhesive solution in step 3, stir paddle speed 36 r / min, dispersion disc linear speed 46 m / s, running time 60 min;

[0037] 5) Preparation of slurry: Add sodium iron-nickel-manganese evenly in three portions. After each addition, the stirring speed is 31 r / min, the dispersion disc linear velocity is 31 m / s, and the running time is 45 min.

[0038] After the above 5 steps, the prepared slurry has a solid content of 71.4% and a viscosity of 10326 cp. The slurry has low fineness, good sieving performance, and does not freeze within 24 hours.

[0039] Example 2

[0040] This embodiment provides a sodium-ion secondary battery positive electrode slurry, and the preparation method is as follows:

[0041] 1) Weigh sodium vanadium phosphate, conductive agent, binder, and dispersant according to the following mass ratio: The mass ratio of the above four substances is 95:2:2.8:0.2; the conductive agent is graphene; the binder is PVDF and polyacrylonitrile in a mass ratio of 1:1; the dispersant is sodium polyaspartate; the total weight of the powder is 310 kg.

[0042] 2) Weigh NMP and add it to a 600L dual-paddle dual-dispersion apparatus. The mass ratio of NMP to the total mass of all substances in step 1 is 0.8.

[0043] 3) Preparation of adhesive solution: Add the adhesive polyacrylonitrile, adhesive PVDF and dispersant to NMP in step 2 in sequence. The stirring speed is 30 r / min, the dispersion disc linear velocity is 35 m / s, and the running time is 140 min.

[0044] 4) Preparation of conductive adhesive: Add conductive agent graphene to the adhesive solution in step 3, stir paddle speed 40 r / min, dispersion disc linear speed 45 m / s, running time 80 min;

[0045] 5) Preparation of slurry: Add sodium vanadium phosphate evenly in three portions. After each addition, the stirring speed is 30 r / min, the dispersion disc linear velocity is 30 m / s, and the running time is 60 min.

[0046] After the above 5 steps, the prepared slurry has a solid content of 55.6% and a viscosity of 10621 cp. The slurry has low fineness, good sieving performance, and does not jelly within 24 hours.

[0047] Example 3

[0048] This embodiment provides a sodium-ion secondary battery positive electrode slurry, and the preparation method is as follows:

[0049] 1) Weigh Prussian white, conductive agent, binder, and dispersant according to the following mass ratio: The mass ratio of the above four substances is 94:3:2.5:0.5; the conductive agent is acetylene black; the binder is PVDF and polyacrylonitrile in a mass ratio of 1:1; the dispersant is sodium polyaspartate; the total weight of the powder is 420 kg.

[0050] 2) Weigh NMP and add it to a 600L dual-paddle dual-dispersion apparatus. The mass ratio of NMP to the total mass of all substances in step 1 is 0.6.

[0051] 3) Preparation of adhesive solution: Add the binder and dispersant to NMP in step 2 in sequence, with a stirring speed of 28 r / min, a dispersion disc linear velocity of 37 m / s, and a running time of 120 min;

[0052] 4) Preparation of conductive adhesive: Add conductive agent acetylene black to the adhesive solution in step 3, stir paddle speed 42 r / min, dispersion disc linear velocity 43 m / s, running time 60 min;

[0053] 5) Preparation of slurry: Prussian white is added evenly in three portions. After each addition, the stirring speed is 35 r / min, the dispersion disc linear velocity is 36 m / s, and the running time is 45 min.

[0054] After the above 5 steps, the prepared slurry has a solid content of 62.5% and a viscosity of 9857 cp. The slurry has low fineness, good sieving performance, and does not jelly within 24 hours.

[0055] Comparative Example 1

[0056] The sodium-ion secondary battery positive electrode slurry differs from that in Example 1 only in that the binder is PVDF and does not contain polyacrylonitrile.

[0057] Comparative Example 2

[0058] The sodium-ion secondary battery positive electrode slurry differs from that in Example 2 only in that the binder is PVDF and does not contain polyacrylonitrile.

[0059] Comparative Example 3

[0060] The sodium-ion secondary battery positive electrode slurry differs from that in Example 3 only in that the binder is PVDF and does not contain polyacrylonitrile.

[0061] Comparative Example 4

[0062] The sodium-ion secondary battery positive electrode slurry differs from that in Example 1 only in that the binder is only polyacrylonitrile and does not contain PVDF.

[0063] Comparative Example 5

[0064] The sodium-ion secondary battery positive electrode slurry differs from that in Example 1 only in that the mass ratio of binder PVDF to polyacrylonitrile is 0.5:9.5.

[0065] Comparative Example 6

[0066] The sodium-ion secondary battery positive electrode slurry differs from that in Example 1 only in that the mass ratio of PVDF binder to polyacrylonitrile is 9.5:0.5.

[0067] Experimental Example

[0068] The positive electrode slurries from Examples 1-3 and Comparative Examples 1-6 were coated onto 15-micron aluminum foil, dried at 95°C, and rolled to obtain positive electrode sheets. Further slitting and winding yielded 26650 cylindrical sodium-ion secondary batteries. Cycle life testing method: The prepared batteries were subjected to a cycle test at 25°C for N cycles. The discharge capacity of the battery in the Nth cycle and the first cycle was recorded, and the discharge retention rate was calculated. Discharge retention rate = (Nth discharge capacity / First discharge capacity) × 100%. The cycle test was terminated when the discharge retention rate reached 80%, and the number of cycles was recorded. The results are shown in the table below.

[0069]

[0070] As shown in the table above, without the addition of polyacrylonitrile and dispersant in the bonding process, the slurry exhibits a jelly-like phenomenon shortly after standing, resulting in numerous coating scratches and a relatively low cycle life. Comparative Examples 4 and 5 show that without PVDF or with insufficient PVDF, the contact between the positive electrode material and the aluminum foil is relatively poor, leading to a lower cycle life. Comparative Example 6 shows that with insufficient polyacrylonitrile, the slurry is prone to jelly-like formation, resulting in numerous coating scratches and a poor cycle life.

[0071] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A sodium-ion secondary battery positive electrode slurry, characterized in that, include: Sodium ion cathode material, conductive agent, binder composition, dispersant; The adhesive composition comprises polyacrylonitrile and polyvinylidene fluoride in a mass ratio of (1-8):(2-9). In the sodium-ion secondary battery positive electrode slurry, the mass ratio of sodium-ion positive electrode material, conductive agent, binder composition and dispersant is (90-96):(1-5):(1-4):(0.1-1); The dispersant is sodium polyaspartate.

2. The sodium-ion secondary battery positive electrode slurry according to claim 1, characterized in that, The mass ratio of polyacrylonitrile to polyvinylidene fluoride in the adhesive composition is 1:(1-2).

3. The sodium-ion secondary battery positive electrode slurry according to claim 1, characterized in that, The binder composition is present in the sodium-ion secondary battery positive electrode slurry at a content of 1-4 wt%.

4. The sodium-ion secondary battery positive electrode slurry according to claim 3, characterized in that, In the sodium-ion secondary battery positive electrode slurry, the mass ratio of sodium-ion positive electrode material, conductive agent, binder composition and dispersant is (90-96):(1-5):(1-4):(0.1-1).

5. The sodium-ion secondary battery positive electrode slurry according to claim 4, characterized in that, In the sodium-ion secondary battery positive electrode slurry, the mass ratio of sodium-ion positive electrode material, conductive agent, binder composition and dispersant is (94-95.5):(1.5-3):(2.5-2.8):(0.2-0.5).

6. The sodium-ion secondary battery positive electrode slurry according to claim 4 or 5, characterized in that, The sodium ion cathode material is selected from one or more of sodium iron-nickel-manganese oxide, sodium vanadium phosphate, Prussian white, and sodium vanadium fluorophosphate; and / or, The conductive agent is selected from one or more of acetylene black, carbon black, carbon nanotubes, and graphene; and / or, The sodium-ion secondary battery positive electrode slurry also includes N-methylpyrrolidone (NMP).

7. The sodium-ion secondary battery positive electrode slurry according to claim 6, characterized in that, In the sodium-ion secondary battery positive electrode slurry, the mass ratio of N-methylpyrrolidone to the sum of the masses of sodium-ion positive electrode material, conductive agent, binder composition and dispersant is (0.1-1):

1.

8. The sodium-ion secondary battery positive electrode slurry according to claim 7, characterized in that, The ratio of the mass of N-methylpyrrolidone to the sum of the masses of the sodium ion cathode material, the conductive agent, the binder composition, and the dispersant is (0.4-0.8):

1.

9. The method for preparing the sodium-ion secondary battery positive electrode slurry according to any one of claims 1-8, characterized in that, include: N-methylpyrrolidone is mixed with the binder composition and dispersant to form a glue solution; the glue solution is mixed with a conductive agent to form a conductive glue solution, and then sodium ion positive electrode material is added and mixed.

10. The use of the sodium-ion secondary battery positive electrode slurry according to any one of claims 1-8 in the preparation of sodium-ion secondary batteries.

11. A positive electrode sheet for a sodium-ion secondary battery, characterized in that, Includes the sodium-ion secondary battery positive electrode slurry according to any one of claims 1-8.

12. A sodium-ion secondary battery, characterized in that, It includes the positive electrode sheet as described in claim 11 or the sodium-ion secondary battery positive electrode slurry as described in any one of claims 1-8.

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