A sodium ion battery positive electrode sheet, a sodium ion battery, and a preparation method and system thereof

Abstract

The present invention relates to the field of sodium ion batteries, and in particular to a sodium ion battery positive electrode sheet, a sodium ion battery, and a preparation method and system thereof. The sodium ion battery positive electrode sheet is composed of the following layers: an intermediate layer; a first functional layer coated on one side of the intermediate layer and a second functional layer coated on the other side of the intermediate layer; a first positive electrode active material coating coated on the first functional layer, and a second positive electrode active material coating coated on the second functional layer; the thickness of the first functional layer and the thickness of the second functional layer are 0.5 to 1.5 μm. The present invention effectively inhibits the reaction of NaOH / Na2CO3 on the surface of the sodium ion positive electrode material with aluminum foil, and inhibits the breakage phenomenon during the rolling process; it also inhibits the problem of excessive positive electrode sheet resistance caused by the reaction products of NaOH / Na2CO3 and aluminum foil, which ultimately leads to excessive battery resistance and poor battery cycle life, effectively improving the capacity and cycle life of the sodium ion battery.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion batteries, and in particular to a sodium ion battery positive electrode sheet, a sodium ion battery, and a preparation method and system thereof. Background Art

[0002] In the 21st century, lithium batteries have been used in numerous applications, including mobile phones, computers, wearable devices, electric vehicles, two-wheeled bicycles, power tools, and streetlights. With the increasing use of lithium batteries, lithium resource consumption has increased rapidly, with production growth failing to keep pace with consumption. This is due to two factors: first, lithium resources are limited, primarily existing in the form of spodumene ore and salt lake lithium; second, lithium cannot be extracted from salt lakes in winter, leading to a surge in the price of lithium metal and compounds this year. In contrast, sodium is widely available and abundant, with reserves 420 times greater than lithium, making it significantly cheaper. In recent years, as lithium prices have skyrocketed, sodium-ion batteries have attracted widespread attention due to their potential to offer 30-50% lower costs than lithium-ion batteries. They hold particularly attractive prospects in energy storage, hybrid power, and as replacements for lead-acid batteries.

[0003] Currently, the main cathode materials for sodium-ion batteries include Prussian blue, sodium vanadium phosphate, and sodium iron-nickel manganate. The preparation process for sodium-ion battery cathode materials requires the addition of excess sodium to obtain a well-crystalline cathode material. Therefore, sodium-ion cathode materials often contain a small amount of residual sodium (existing as Na2O at high temperatures). Once the temperature drops to room temperature, Na2O absorbs CO2 and H2O from the air to form NaOH and Na2CO3, making the cathode material alkaline. Furthermore, Na is more alkaline than Li, so the alkalinity of sodium-ion cathode materials is much higher than that of lithium-ion cathode materials.

[0004] Sodium-ion battery positive electrodes use aluminum foil, the current collector used for lithium-ion battery positive electrodes. The NaOH and Na2CO3 on the surface of the sodium-ion positive electrode material react with the aluminum foil to a certain extent, causing the electrode to easily break during rolling, affecting the product's processing performance. To prevent electrode breakage, reducing the electrode compaction density can reduce the frequency of breakage to a certain extent, but it cannot fundamentally solve the problem of electrode breakage, let alone meet the product's capacity design requirements. Another consequence of the reaction between the NaOH and Na2CO3 on the surface of the sodium-ion positive electrode material and the aluminum foil is that the reaction products cause the electrode resistance to be too high, ultimately leading to excessive battery resistance and ultimately a decrease in battery cycle life. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a sodium ion battery positive electrode sheet, a sodium ion battery and a preparation method and system thereof.

[0006] In the first aspect, the sodium ion battery positive electrode plate provided by the present invention is composed of the following five layers: an intermediate layer, a first functional layer close to one side of the intermediate layer, a second functional layer close to the other side of the intermediate layer, a first sodium ion positive electrode slurry coating layer close to the first functional layer, and a second sodium ion positive electrode slurry coating layer close to the second functional layer; the intermediate layer is aluminum foil, the first functional layer and the second functional layer are alkaline blocking conductive functional layers, and the thickness of the first functional layer and the thickness of the second functional layer are both 0.5 to 1.5 μm. The positive electrode sheet provided by the present invention is composed of a five-layer structure. The functional layers (first functional layer and second functional layer) close to the upper and lower surfaces of the aluminum foil play a role in hindering the reaction of NaOH / Na2CO3 on the surface of the sodium ion positive electrode material with the aluminum foil and providing conductivity. The positive electrode sheet of the present invention effectively inhibits the reaction of NaOH / Na2CO3 on the surface of the sodium ion positive electrode material with the aluminum foil, inhibiting the phenomenon of belt breakage during the rolling process; it also inhibits the problem of excessive resistance of the positive electrode sheet caused by the reaction product of NaOH / Na2CO3 and the aluminum foil, ultimately leading to excessive battery resistance and poor battery cycle life, effectively improving the capacity and cycle life of the sodium ion battery. The present invention has found that the functional layer can better inhibit the phenomenon of belt breakage during the rolling process at a specific thickness, improving the improvement effect of the capacity and cycle life of the sodium ion battery.

[0007] Preferably, the thickness of the first functional layer is 0.9-1.1 μm.

[0008] Preferably, the thickness of the second functional layer is 0.9-1.1 μm.

[0009] Preferably, the thickness of the first sodium ion positive electrode slurry coating layer is 30 to 200 μm, preferably 50 to 150 μm.

[0010] Preferably, the thickness of the second sodium ion positive electrode slurry coating layer is 30 to 200 μm, preferably 50 to 150 μm.

[0011] Preferably, the thickness of the intermediate layer is 10 to 20 μm, and more preferably 12 to 15 μm.

[0012] Further research in the present invention found that when the first functional layer and the second functional layer both adopt the preferred thickness range (0.9 to 1.1 μm), the effect is more significantly improved; in order to further improve the performance of the positive electrode sheet and increase the capacity and cycle life of the sodium ion battery, the present invention optimizes the thickness of the sodium ion positive electrode slurry coating layer and the intermediate layer combined with the functional layer. The above-mentioned functional layer combined with the sodium ion positive electrode slurry coating layer and the intermediate layer of a specific thickness can better exert the ionic conductivity and electronic conductivity of lithium ions, further improving the capacity and cycle life of the sodium ion battery.

[0013] Preferably, the first functional layer and the second functional layer are prepared from a functional slurry comprising the following raw materials: a first conductive agent, an alkaline blocker, a first binder, and a dispersant. The mass ratio of the first conductive agent, the alkaline blocker, the first binder, and the dispersant is preferably 30-55:40-65:1-5:0.1-2; preferably, the alkaline blocker is selected from one or more of AL2O3, AlCl3, and AlBr3.

[0014] More preferably, the first conductive agent is selected from one or more of acetylene black, carbon black, VGCF, carbon nanotubes, and graphene, preferably acetylene black.

[0015] More preferably, the first binder is selected from polyvinylidene fluoride and / or polyacrylate.

[0016] More preferably, the dispersant is selected from one or more of polyvinyl pyrrolidone and sodium polyacrylate.

[0017] Further preferably, the first sodium ion positive electrode slurry coating layer and the second sodium ion positive electrode slurry coating layer are prepared from the following raw materials: a positive electrode active material, a second conductive agent, a second binder and NMP; preferably, the positive electrode active material is sodium vanadium phosphate, sodium nickel cobalt manganate or Prussian blue compound; the second conductive agent is selected from one or more of acetylene black, carbon black, carbon nanotubes, and graphene; the second binder is polyvinylidene fluoride or polyacrylic acid; and the slurry solid content is 45-65%.

[0018] The present invention further discovered that the alkaline blocking agents Al2O3, AlCl3, and AlBr3 in the functional layer react with NaOH and Na2CO3 on the surface of the sodium-ion positive electrode material, thereby better preventing NaOH and Na2CO3 from corroding the aluminum foil, increasing the compaction density of the positive electrode sheet, and suppressing the phenomenon of belt breakage during the rolling process. This suppresses the problem of excessive positive electrode sheet resistance caused by the reaction products of NaOH / Na2CO3 and the aluminum foil, which ultimately leads to excessive battery resistance and ultimately a decrease in battery cycle life, effectively improving the capacity and cycle life of the sodium-ion battery. Simultaneously, the addition of conductive agents such as acetylene black, carbon black, VGCF, carbon nanotubes, and graphene, preferably acetylene black, to the functional layer further overcomes the problems of excessive sheet resistance and decreased cycle life caused by the addition of Al2O3, AlCl3, and AlBr3. Furthermore, the functional layer is formulated with optimized and screened raw materials in the above-mentioned mass ratio, which can further enhance the effect.

[0019] Preferably, the functional slurry has a solid content of 6 to 20%, and the functional slurry preferably includes NMP. In the present invention, the raw materials for the first and second functional layers preferably also include NMP. Preferably, the first conductive agent, alkaline blocking agent, first binder, and dispersant are mixed with NMP to obtain a functional slurry with a solid content of 6 to 20%. The functional slurry with a solid content of 6 to 20% obtained by mixing the raw materials for the functional layer of the present invention with NMP facilitates the better preparation of a functional layer with excellent performance and obtains a functional layer of a specific thickness (0.9 to 1.1 μm).

[0020] In a second aspect, the present invention provides a method for preparing the positive electrode sheet of a sodium ion battery, comprising:

[0021] 1) Functional layer coating: coating the functional slurry on the aluminum foil and drying it to obtain the first functional layer and the second functional layer closely attached to the middle layer;

[0022] 2) Preparation of positive electrode sheets: coating the positive electrode slurry on the first functional layer and the second functional layer, drying to obtain a first sodium ion positive electrode slurry coating layer and a second sodium ion positive electrode slurry coating layer closely adhering to the first functional layer and the second functional layer, and then rolling and cutting to obtain positive electrode sheets.

[0023] Preferably, in step 1), the thickness of a single wet film is 2 to 5 μm; the coating speed is 20 to 100 m / min, the drying temperature is 80 to 130° C., and the drying time is 0.5 to 3 min; the thickness of a single functional layer after drying is 0.5 to 1.5 μm; and / or,

[0024] Further preferably, in step 2), the coating speed is 10 to 30 m / min, the drying temperature is 80 to 130° C., and the drying time is 3 to 5 min;

[0025] The preparation of the preferred functional slurry of the present invention includes: dry mixing a first conductive agent, an alkaline blocking agent, a first binder, and a dispersant, and then adding NMP to mix the slurry; further preferably, the dry mixing time is 30-60 minutes; during the slurry mixing, the stirring paddle speed is 10-40 r / min, the dispersion disk linear speed is 15-50 m / s, and NMP is preferably added evenly in three times, with each treatment time being 30-60 minutes; the solid content of the functional slurry is 6-20%.

[0026] In a third aspect, the present invention further provides a sodium ion battery, comprising a sodium ion battery positive electrode sheet, a negative electrode sheet, an electrolyte and a diaphragm, wherein the positive electrode sheet is the above-mentioned sodium ion battery positive electrode sheet or the sodium ion battery positive electrode sheet obtained by the above-mentioned preparation method.

[0027] Further preferably, the sodium ion battery is a 32140 cylindrical sodium ion battery.

[0028] Preferably, the negative electrode plate is composed of a negative electrode active material, a conductive agent, a binder, and a current collector.

[0029] Preferably, the negative electrode active material is a hard carbon material; and / or the conductive agent is selected from one or more of acetylene black, carbon black, carbon nanotubes, and graphene; and / or the binder is CMC and / or SBR; and / or the current collector is copper foil or aluminum foil.

[0030] Preferably, the diaphragm is made of polyethylene, polypropylene, polyvinylidene fluoride or aramid.

[0031] Preferably, the electrolyte is composed of an organic solvent and an electrolyte sodium salt. Preferably, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, ethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and methyl tert-butyl ether; and the electrolyte sodium salt is selected from one or more of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, and sodium perchlorate.

[0032] In a fourth aspect, the present invention provides a manufacturing system for the sodium ion battery positive electrode sheet, comprising a unwinding shaft, a transfer shaft, a functional layer coating unit, a first drying device, an active material coating unit, a second drying device and a winding shaft connected in sequence.

[0033] Further preferably, the functional layer coating unit is provided with a micro-gravure coating device, and the active material coating unit is provided with a slurry coating device.

[0034] The present invention has at least the following beneficial effects: the positive electrode sheet of the present invention effectively inhibits the reaction between NaOH / Na2CO3 on the surface of the sodium-ion positive electrode material and the aluminum foil, thereby preventing the phenomenon of strip breakage during the rolling process. It also prevents the problem of excessive positive electrode sheet resistance caused by the reaction products of NaOH / Na2CO3 and the aluminum foil, which ultimately leads to excessive battery resistance and a decrease in battery cycle life, thereby effectively improving the capacity and cycle life of the sodium-ion battery. Research in the present invention has found that the functional layer, at a specific thickness, can better inhibit the phenomenon of strip breakage during the rolling process, improving the capacity and cycle life of the sodium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 Schematic diagram of a manufacturing system for a sodium ion battery positive electrode sheet provided in an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the structure of the positive electrode sheet of a sodium ion battery provided in an embodiment of the present invention;

[0038] Reference numerals:

[0039] 1: Unwinding axis; 2: Transfer axis; 3: Functional layer coating unit;

[0040] 4: Micro-gravure coating equipment; 5: First drying equipment; 6: Active material coating unit;

[0041] 7: Slurry coating equipment; 8: Second drying equipment; 9: Rewinding shaft;

[0042] 10: first sodium ion positive electrode slurry coating layer; 11: first functional layer;

[0043] 12: middle layer; 13: second functional layer;

[0044] 14: Second sodium ion positive electrode slurry coating layer. DETAILED DESCRIPTION

[0045] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0046] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased through regular channels.

[0047] In the description of the embodiments of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "first" and "second" are used to clearly illustrate the numbering of product components and do not represent any substantial difference. "Up," "down," "inside," etc. are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0048] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0049] The following combination Figure 1-Figure 2 The present invention describes a sodium ion battery positive electrode sheet, a sodium ion battery and a system thereof.

[0050] like Figure 1 The figure shows a manufacturing system for a sodium-ion battery positive electrode sheet used in an embodiment of the present invention, which includes a winding shaft 1, a transfer shaft 2, a functional layer coating unit 3, a first drying device 5, an active material coating unit 6, a second drying device 8 and a winding shaft 9 connected in sequence; the functional layer coating unit 3 is provided with a functional layer coating device, which is a micro-gravure coating device 4, and the active material coating unit 6 is provided with a slurry coating device 7.

[0051] like Figure 2 The following is a schematic diagram of the structure of a sodium-ion battery positive electrode sheet provided in the following embodiment of the present invention. The sodium-ion battery positive electrode sheet is composed of the following five layers: an intermediate layer 12, a first functional layer 11 close to one side of the intermediate layer 12, a second functional layer 13 close to the other side of the intermediate layer 12, a first sodium-ion positive electrode slurry coating layer 10 close to the first functional layer 11, and a second sodium-ion positive electrode slurry coating layer 14 close to the second functional layer 13; the intermediate layer 12 is aluminum foil, and the first functional layer 11 and the second functional layer 13 are alkaline blocking conductive functional layers. To further improve the capacity and cycle life of the sodium-ion battery, the thickness of the first functional layer 11 is 0.9 to 1.1 μm; the thickness of the second functional layer 13 is 0.9 to 1.1 μm.

[0052] To further improve the performance of the positive electrode sheet, the present invention optimizes the thickness of the sodium-ion positive electrode slurry coating layer and the intermediate layer combined with the functional layer. Specifically, the thickness of the first sodium-ion positive electrode slurry coating layer is 50-150 μm; the thickness of the second sodium-ion positive electrode slurry coating layer is 50-150 μm. The intermediate layer is aluminum foil with a thickness of 12-15 μm. When both the first and second functional layers are within the preferred thickness range, the performance is significantly improved. Furthermore, the present invention has discovered that optimizing the thickness of the sodium-ion positive electrode slurry coating layer and the intermediate layer, combined with the specific thickness of the sodium-ion positive electrode slurry coating layer and the intermediate layer, can enhance their performance and improve the capacity and cycle life of the sodium-ion battery. In embodiments of the present invention, the alkaline blocking material is preferably Al2O3, AlCl3, or AlBr3, and the conductive material is preferably acetylene black, carbon black, VGCF, carbon nanotubes, or graphene.

[0053] The sodium ion battery provided by the present invention comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The positive electrode sheet is the aforementioned positive electrode sheet. Preferably, the current collector of the negative electrode sheet is copper foil or aluminum foil, and the negative electrode slurry layer covering the current collector comprises a hard carbon material as the negative electrode active material. The separator is polyethylene, polypropylene, polyvinylidene fluoride, or aramid. Furthermore, the sodium ion battery is a 32140 cylindrical sodium ion battery.

[0054] Example 1

[0055] In the sodium ion battery positive electrode sheet provided in this embodiment, the thickness of the first sodium ion positive electrode slurry coating layer 10 and the second sodium ion positive electrode slurry coating layer 14 are both 110 μm, the thickness of the first functional layer 11 and the second functional layer 13 are both 1.0 μm, and the thickness of the intermediate layer 12 is both 15 μm.

[0056] This embodiment also provides a method for preparing the positive electrode sheet of the sodium ion battery, which is as follows:

[0057] Preparation of a functional layer slurry

[0058] 1) Dry mix the conductive agent, alkaline blocker, binder, and dispersant in a 200L V-type mixer for 30-60 minutes. The weight ratio of the conductive agent, alkaline blocker, binder, and dispersant is 45:53:1.5:0.5, and the total weight of these materials is 80 kg. The conductive agent is acetylene black; the alkaline blocker is Al2O3; the binder is polyvinylidene fluoride; and the dispersant is polyvinylpyrrolidone.

[0059] 2) The mixture in 1) was transferred to a 600L slurry mixing tank, and NMP was evenly added in three times. After each addition of NMP, the stirring paddle speed was 35r / min, the dispersion disk linear speed was 45m / s, the operation time was 60min, and the total amount of NMP added was 446.32Kg; after step 2, a functional layer slurry with a solid content of 15.2% was obtained.

[0060] Two functional layer coating

[0061] The functional layer slurry was coated in a micro-gravure coater, and the thickness of the single-layer wet film was controlled at 2 μm; the coating speed was 60 m / min, the drying temperature was 120° C., and the drying time was 1.5 min; after drying, the thickness of the single-layer functional layer was controlled at 1 μm.

[0062] Preparation of three positive electrode sheets

[0063] 1) Apply the positive electrode slurry to the functional layer at a coating speed of 20 m / min, a drying temperature of 115°C, and a drying time of 3 minutes. The positive electrode slurry consists of four components: positive electrode active material, conductive agent, binder, and NMP. The positive electrode active material is sodium vanadium phosphate; the conductive agent can be acetylene black; the binder can be polyvinylidene fluoride. The mass ratio of the three is 96:2:2. The slurry solids content is 55%.

[0064] 2) The dried coated sheet in step 1 is rolled and cut to obtain a positive electrode sheet.

[0065] Comparative Example 1

[0066] In Example 1, the positive electrode current collector (intermediate layer) is made of aluminum foil with a thickness of 15 μm, and no functional layer is used. Other aspects are the same as in Example 1.

[0067] Example 2

[0068] In the sodium ion battery positive electrode sheet provided in this embodiment, the thickness of the first sodium ion positive electrode slurry coating layer 10 and the second sodium ion positive electrode slurry coating layer 14 are both 125 μm, the thickness of the first functional layer 11 and the second functional layer 13 are both 1.0 μm, and the thickness of the intermediate layer 12 is both 15 μm.

[0069] This embodiment also provides a method for preparing the positive electrode sheet of the sodium ion battery, which is as follows:

[0070] Preparation of a functional layer slurry

[0071] 1) Dry mix the conductive agent, alkaline blocker, binder, and dispersant in a 200L V-type mixer for 30-60 minutes. The weight ratio of conductive agent, alkaline blocker, binder, and dispersant is 35:63:1.5:0.5, with a total weight of 90 kg. The conductive agent is acetylene black; the alkaline blocker is AlCl3; the binder is polyvinylidene fluoride; and the dispersant is polyvinylpyrrolidone.

[0072] 2) The mixture in 1) was transferred to a 600 L slurry mixing tank, and NMP was evenly added in three times. After each NMP addition, the stirring blade speed was 35 r / min, the dispersion disk linear speed was 45 m / s, the running time was 60 min, and the total amount of NMP added was 455.46 kg;

[0073] After step 2, a functional layer slurry with a solid content of 16.5% is obtained.

[0074] Two functional layer coating

[0075] The functional layer slurry was coated in a micro-gravure coater, and the thickness of the coated single-layer wet film was controlled at 2 μm; the coating speed was 60 m / min, the drying temperature was 115° C., and the drying time was 2 min; after drying, the thickness of the single-layer functional layer was controlled at 1 μm.

[0076] Preparation of three positive electrode sheets

[0077] 1) Apply the positive electrode slurry to the functional layer at a coating speed of 20 m / min, drying temperature at 115°C, and drying time for 3 minutes. The positive electrode slurry consists of four components: positive electrode active material, conductive agent, binder, and NMP. The positive electrode active material is sodium iron nickel manganese oxide; the conductive agent is acetylene black; and the binder can be polyvinylidene fluoride. The mass ratio of the three is 96:2:2. The slurry has a solids content of 75%.

[0078] 2) The dried coated sheet in step 1 is rolled and cut to obtain a positive electrode sheet.

[0079] Comparative Example 2

[0080] In Example 2, the positive electrode current collector (intermediate layer) is made of aluminum foil with a thickness of 15 μm, and no functional layer is used. Other aspects are the same as in Example 2.

[0081] Example 3

[0082] In the sodium ion battery positive electrode sheet provided in this embodiment, the thickness of the first sodium ion positive electrode slurry coating layer 10 and the second sodium ion positive electrode slurry coating layer 14 are both 105 μm, the thickness of the first functional layer 11 and the second functional layer 13 are both 1.1 μm, and the thickness of the intermediate layer 12 is both 12 μm.

[0083] This embodiment also provides a method for preparing the positive electrode sheet of the sodium ion battery, which is as follows:

[0084] Preparation of a functional layer slurry

[0085] 1) Dry mix the conductive agent, alkaline blocker, binder, and dispersant in a 200L V-type mixer for 30-60 minutes. The weight ratio of conductive agent, alkaline blocker, binder, and dispersant is 40:58:1.5:0.5, with a total weight of 85 kg. The conductive agent is acetylene black; the alkaline blocker is AlBr3; the binder is polyvinylidene fluoride; and the dispersant is polyvinylpyrrolidone.

[0086] 2) The mixture in 1) was transferred to a 600 L slurry mixing tank, and NMP was evenly added in three times. After each NMP addition, the stirring paddle speed was 30 r / min, the dispersion plate linear speed was 40 m / s, and the running time was 60 min. The total amount of NMP added was 459.87 kg.

[0087] After step 2, a functional layer slurry with a solid content of 15.6% is obtained.

[0088] Two functional layer coating

[0089] The functional layer slurry was coated in a micro-gravure coater, and the thickness of the single-layer wet film was controlled at 2 μm; the coating speed was 60 m / min, the drying temperature was 110° C., and the drying time was 2.5 min; after drying, the thickness of the single-layer functional layer was controlled at 1.1 μm.

[0090] Preparation of three positive electrode sheets

[0091] 1) Apply the positive electrode slurry onto the functional layer at a coating speed of 25 m / min, drying at 115°C for 3 minutes. The positive electrode slurry consists of four components: positive electrode active material, conductive agent, binder, and NMP. The positive electrode active material is Prussian white; the conductive agent is acetylene black; and the binder can be polyvinylidene fluoride. The mass ratio of the three is 96:2:2. The slurry has a solids content of 59%.

[0092] 2) The dried coated sheet in step 1 is rolled and cut to obtain a positive electrode sheet.

[0093] Comparative Example 3

[0094] In Example 3, the positive electrode current collector (intermediate layer) is made of aluminum foil with a thickness of 12 μm, and no functional layer is used. Other aspects are the same as in Example 2.

[0095] Example 4

[0096] The positive electrode sheets of the embodiment and the comparative example were used to prepare 32140 cylindrical sodium ion batteries according to the following method.

[0097] 1. Positive electrode

[0098] The positive electrode sheets provided in the examples and comparative examples were used.

[0099] 2. Negative electrode

[0100] 95.5wt% hard carbon, 1% acetylene black, 1.5% CMC, and 2% SBR were added to purified water and dispersed evenly to prepare a negative electrode slurry. The negative electrode slurry was evenly coated on the surface of copper foil, dried, rolled, and cut to obtain a negative electrode.

[0101] 3. Diaphragm

[0102] The diaphragm is made of polyethylene (PE) porous polymer film.

[0103] 4. Electrolyte

[0104] 16g of sodium hexafluorophosphate, 25g of ethylene carbonate, 52g of dimethyl carbonate, 6g of diethylene glycol dimethyl ether, and 1g of methyl methylthiosulfonate were mixed evenly to prepare an electrolyte.

[0105] The positive electrode sheet, separator, and negative electrode sheet are wound into an electrode group, and then grooved, liquid-filled, and sealed to form a 32140 cylindrical sodium-ion battery.

[0106] The maximum compaction density test method of the electrode is as follows: the coated electrode is cut into 100mm*100mm pieces and then passed through a rolling roller. The rolled electrode is folded in half and then laid flat. The part facing each other is light-transmitting but not broken, which is the maximum compaction density of the electrode. The compaction density of the electrode = the surface density of the electrode powder coating / (the thickness of the electrode - the thickness of the current collector).

[0107] Cycle life test method: At 25°C, the batteries prepared in the examples and comparative examples were charged at a 0.5C rate to 3.9V / 4.2V and discharged at a 0.5C rate to 2V. Full charge and discharge cycles were performed until the capacity of the sodium ion battery was less than 80% of the initial capacity. The number of cycles was recorded. The specific data is shown in Table 1. It can be seen that the sodium ion positive electrode sheet prepared using the present invention has a higher compaction density, lower internal resistance, and better cycle life.

[0108] Table 1 Test results

[0109]

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A sodium ion battery positive electrode plate, characterized in that: It is composed of the following five layers: an intermediate layer, a first functional layer close to one side of the intermediate layer, a second functional layer close to the other side of the intermediate layer, a first sodium ion positive electrode slurry coating layer close to the first functional layer, and a second sodium ion positive electrode slurry coating layer close to the second functional layer; the intermediate layer is aluminum foil, the first functional layer and the second functional layer are alkaline blocking conductive functional layers, and the thickness of the first functional layer and the thickness of the second functional layer are both 0.9-1.1 μm; the thickness of the first sodium ion positive electrode slurry coating layer and the second sodium ion positive electrode slurry coating layer is 30-200 μm, and the thickness of the intermediate layer is 10-20 μm; The first functional layer and the second functional layer are prepared from a functional slurry comprising the following raw materials: a first conductive agent, an alkaline blocker, a first binder, and a dispersant, wherein the alkaline blocker is selected from one or more of Al2O3, AlCl3, and AlBr3; the first conductive agent is selected from one or more of acetylene black, carbon black, VGCF, carbon nanotubes, and graphene; the first binder is polyvinylidene fluoride and / or polyacrylate; the dispersant is polyvinyl pyrrolidone and / or sodium polyacrylate; the mass ratio of the first conductive agent, alkaline blocker, first binder, and dispersant is 30-55:40-65:1-5:0.1-2; The first sodium ion positive electrode slurry coating layer and the second sodium ion positive electrode slurry coating layer are prepared from the following raw materials: a positive electrode active material, a second conductive agent, a second binder and NMP, the positive electrode active material is sodium vanadium phosphate, sodium nickel cobalt manganate or Prussian blue compound; the second conductive agent is selected from one or more of acetylene black, carbon black, carbon nanotubes, and graphene; the second binder is polyvinylidene fluoride or polyacrylic acid.

2. The sodium ion battery positive electrode sheet according to claim 1, characterized in that The thickness of the first sodium ion positive electrode slurry coating layer is 50-150 μm; and / or the thickness of the second sodium ion positive electrode slurry coating layer is 50-150 μm; And / or, the thickness of the intermediate layer is 12-15 μm.

3. The sodium ion battery positive electrode sheet according to claim 1 or 2, characterized in that: The raw materials for preparing the first sodium ion positive electrode slurry coating layer and the second sodium ion positive electrode slurry coating layer have a slurry solid content of 45-65%.

4. The method for preparing a positive electrode sheet for a sodium ion battery according to any one of claims 1 to 3, characterized in that: include: 1) Functional layer coating: coating the functional slurry on the aluminum foil and drying it to obtain the first functional layer and the second functional layer close to the middle layer; 2) Preparation of positive electrode sheets: coating the positive electrode slurry on the first functional layer and the second functional layer, drying to obtain a first sodium ion positive electrode slurry coating layer and a second sodium ion positive electrode slurry coating layer closely adhering to the first functional layer and the second functional layer, and then rolling and cutting to obtain positive electrode sheets.

5. The method for preparing a positive electrode sheet for a sodium ion battery according to claim 4, wherein: In step 1), the thickness of the single wet film is 2-5 μm; the coating speed is 20-100 m / min, the drying temperature is 80-130°C, and the drying time is 0.5-3 min; the thickness of the single functional layer after drying is 0.5-1.5 μm; and / or, In step 2), the coating speed is 10-30 m / min, the drying temperature is 80-130° C., and the drying time is 3-5 min.

6. The method for preparing a positive electrode sheet for a sodium ion battery according to claim 5, characterized in that: The preparation of the functional slurry includes: dry mixing a first conductive agent, an alkaline blocking agent, a first binder, and a dispersant, and then adding NMP to mix the slurry.

7. The method for preparing a positive electrode sheet for a sodium ion battery according to claim 6, wherein: The dry mixing time is 30-60 minutes; during the slurry mixing, the stirring paddle speed is 10-40 r / min, the dispersion disk linear speed is 15-50 m / s, NMP is evenly added in three times, and each treatment time is 30-60 minutes; the solid content of the functional slurry is 6-20%.

8. A sodium ion battery, characterized in that: It comprises a sodium ion battery positive electrode sheet, a negative electrode sheet, an electrolyte and a separator; the positive electrode sheet is the sodium ion battery positive electrode sheet according to any one of claims 1 to 3 or the sodium ion battery positive electrode sheet obtained by the preparation method according to any one of claims 4 to 7.

9. The sodium ion battery according to claim 8, characterized in that The sodium ion battery is a 32140 cylindrical sodium ion battery.

10. The sodium ion battery according to claim 8, characterized in that The negative electrode plate is composed of a negative electrode active material, a third conductive agent, a third binder and a negative electrode current collector.

11. The sodium ion battery according to claim 10, characterized in that The negative electrode active material is a hard carbon material; and / or the third conductive agent is selected from one or more of acetylene black, carbon black, carbon nanotubes, and graphene; and / or the third binder is CMC and / or SBR; and / or the negative electrode current collector is copper foil or aluminum foil.

12. The sodium ion battery according to claim 8, characterized in that The separator is made of polyethylene, polypropylene, polyvinylidene fluoride or aramid; and / or the electrolyte is composed of an organic solvent and an electrolyte sodium salt.

13. The sodium ion battery according to claim 12, characterized in that The organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, ethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and methyl tert-butyl ether; and / or the electrolyte sodium salt is selected from one or more of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, and sodium perchlorate.

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