Positive electrode sheet and preparation method thereof, and lithium-ion battery

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and in particular to a positive electrode plate and a preparation method thereof, and a lithium-ion battery. The positive electrode plate provided by the present invention includes a main body area, a mixing area and a conductive coating area, wherein the mixing area is a mutually soluble area formed by the main body area material and the conductive coating area material during the coating process; wherein the conductive coating area includes a polymer binder, an isatin anhydride and tris(trimethylsilyl) borate in a mass ratio of (0.3-0.7): (0.2-0.5): (0.1-0.2). The present invention effectively improves the problem of lithium precipitation in the thinning area of the battery by setting a specific composition of the conductive coating area and the mixing area.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a positive electrode plate and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] With increasing environmental pollution, the new energy industry is attracting increasing attention. As a key component of electric vehicles, lithium-ion batteries (Li-ion batteries) have a significant impact on their performance and lifespan, attracting widespread attention. Compared to other housings, aluminum-cased Li-ion batteries are widely used due to their advantages, including light weight, high specific energy, improved safety, and long service life. Li-ion batteries with aluminum metal casings offer excellent heat dissipation and mechanical strength, making them a popular choice among lithium battery manufacturers.

[0003] However, in the existing electrode production process, during the coating process, the fluidity of the electrode slurry causes the slurry thickness or coating surface density at the coating edge (thinning area) to be lower than that in the middle material area (main area), resulting in the Li + The migration path is long and the migration resistance is increased, which can easily lead to lithium deposition in the thinning area. The thickness of the edge of the negative electrode is uneven. Even after rolling, it is still difficult to ensure the flatness of the edge of the electrode. The uneven electrode can easily cause a large overpotential, causing lithium to be deposited on the surface of the negative electrode material, resulting in lithium deposition, which affects the battery performance. The continuous occurrence of lithium deposition can pierce the diaphragm in severe cases, causing an internal short circuit in the battery. On the other hand, due to the fluctuation of the coating surface density, it is easy to cause the ratio of the capacity of the negative electrode sheet in the thinning area to the capacity of the positive electrode sheet (NP ratio) to be too small, which can easily lead to lithium deposition on the surface of the negative electrode in the thinning area during charging. As a result, the lithium deposition in the thinning area worsens during long-term cycling, further causing large-scale lithium deposition inside the battery cell, posing a safety hazard during the use of the battery cell. In addition, in the battery reaction, due to the large local current at the edge of the electrode, the NP ratio of the edge thinning area is too small, which can easily lead to local overcharging at the edge of the negative electrode; local overcharging can easily cause electrolyte decomposition, increase the internal pressure of the battery, and irreversible loss of electrolyte, resulting in battery capacity attenuation and even safety accidents.

[0004] To solve the above problems, the traditional method is generally to increase the surface density of the negative electrode coating to improve the NP ratio of the thinning area and eliminate the risk of lithium deposition in the thinning area. However, the increase in negative electrode material will increase the formation of SEI film and cause the increase in electrolyte consumption. Increasing the NP ratio will consume too much positive electrode active material and reduce the positive electrode specific capacity. In addition, too large a NP ratio can easily cause Li + Excessive losses and deterioration of cycle performance. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the production process of electrode plates in the prior art, thereby providing a positive electrode plate and a preparation method thereof, and a lithium-ion battery.

[0006] To this end, the present invention provides the following technical solutions:

[0007] The present invention provides a positive electrode plate, comprising a main body region, a mixed material region and a conductive coating region, wherein the mixed material region is a mutually soluble region formed by the main body region material and the conductive coating region material during the coating process;

[0008] The conductive coating area comprises a polymer binder, an isatin anhydride and tris(trimethylsilyl)borate in a mass ratio of (0.3-0.7): (0.2-0.5): (0.1-0.2).

[0009] Optionally, the width of the conductive coating area is 3-7 mm.

[0010] Optionally, the width of the mixing zone is 1.0-3.5 mm.

[0011] Optionally, the thickness of the conductive coating area is 10-50% of the thickness of the main body area;

[0012] And / or, the thickness of the main body region is 25-250 μm.

[0013] Optionally, the polymer binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylate, polyimide, polyacrylonitrile, polysilicone ether, and polyethylene oxide resin;

[0014] And / or, the isatin anhydride includes at least one of 5-fluoroisatin anhydride and 6-fluoroisatin anhydride;

[0015] And / or, the positive electrode active material in the main body region is lithium iron phosphate, a ternary lithium battery positive electrode material or a multi-element lithium battery positive electrode material.

[0016] The present invention also provides a method for preparing the above-mentioned positive electrode sheet, comprising the following steps:

[0017] S1, preparing the main area slurry;

[0018] S2, dissolving a polymer binder, isatin anhydride and tris(trimethylsilyl)borate in an organic solvent to obtain a conductive coating slurry;

[0019] S3, coating the main body region slurry and the conductive coating region slurry onto the current collector simultaneously, drying, rolling, and cutting to obtain the positive electrode sheet.

[0020] Optionally, the current collector in the present invention is conventional in the field, for example, aluminum foil is generally used as the positive electrode current collector.

[0021] Optionally, in step S2, the solid content of the conductive coating area slurry is 20-45%;

[0022] And / or, the organic solvent is a commonly used solvent in the field, for example, it can be N-methylpyrrolidone.

[0023] Optionally, in step S3, the drying temperature is 90-120°C.

[0024] Optionally, in step S1, the main region slurry includes: a positive electrode active material, a conductive agent, a binder and a solvent, and its specific composition is conventional in the field and can be adjusted according to the type and model of the battery.

[0025] The present invention also provides a lithium-ion battery, comprising the above-mentioned positive electrode plate or the positive electrode plate prepared by the above-mentioned preparation method.

[0026] By limiting the thickness of the main body area, the present invention covers the high-power thin electrode solutions of conventional hybrid electric vehicles (HEV) and the high-energy thick electrode solutions of pure electric vehicles (EV).

[0027] In the present invention, the positive electrode active material in the main region is a conventional active material in lithium ion batteries, for example, lithium iron phosphate, a ternary lithium battery positive electrode material or a multi-element lithium battery positive electrode material. Typically, but not limited to, the ternary lithium battery positive electrode material includes Li2Ni x Co y Mn z At least one of O2 (0.3≤x≤0.95; 0≤<y≤0.3; 0.05≤z≤0.3), typically, but not limited to, the high nickel ternary positive electrode material includes LiNi 0.9 Co 0.05 Mn 0.05 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.7 Co 0.1 Mn 0.2 O2、LiNi 0.6 Co 0.2 Mn 0.2 One or more kinds of O2, accounting for 80%-95% of the mass in the electrode active layer. The multi-element lithium battery positive electrode material includes Li2Ni x Co y Mn z T n At least one of O2 (0.3≤x≤0.95; 0<y≤0.3; 0.05≤z≤0.3; 0<n≤0.3; T is Al or a transition metal element such as Fe, Cr, Cu, etc.).

[0028] In the present invention, the coating method is well known in the art. Typical non-limiting methods include the following steps: lithium iron phosphate positive electrode material, binder, and conductive agent are mixed in a mass ratio of 94.6:3.7:1.7, and NMP is added to adjust the slurry viscosity. After sufficient stirring, NMP is added to adjust the slurry viscosity to form a positive electrode slurry with a viscosity of 4500 to 8000 mPa·s and a solid content of 60% to 70%. The positive electrode slurry is evenly coated on a 6μm aluminum foil, and the double-sided coating weight is about 50mg / cm 2 .

[0029] Among them, the binder includes one or more of "polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyacrylate, polyimide, polyacrylonitrile, polysiloxane, and polyethylene oxide resin", accounting for 2%-5% of the mass in the electrode active layer.

[0030] Conductive agents include one or more of carbon nanotubes (CNTs), conductive carbon black (SP), Ketjen black, acetylene black, 350G, carbon fiber (VGCF), graphite conductive agent (KS, SO), graphene, etc., and the mass of the electrode active layer accounts for 1.5%-5%.

[0031] In the present invention, other components and preparation methods of the lithium-ion battery provided are conventional in the art.

[0032] The technical solution of the present invention has the following advantages:

[0033] The positive electrode plate provided by the present invention includes a main area, a mixing area and a conductive coating area, wherein the mixing area is a mutually soluble area formed by the main area material and the conductive coating area material during the coating process; wherein the conductive coating area includes a polymer binder, an isatin anhydride and tris(trimethylsilyl) borate in a mass ratio of (0.3-0.7): (0.2-0.5): (0.1-0.2). The present invention effectively improves the problem of lithium plating in the thinning area of the battery by setting a conductive coating area and a mixing area of specific composition. Specifically, 1) by setting a conductive coating in the thinning area, the positive electrode Li in the thinning area is reduced. + content, improve the NP ratio of the thinned area of the battery cell, and eliminate the risk of too small NP ratio caused by polarization and coating tolerance in the thinned area; 2) This setting slows down the thinning trend of the edge thickness of the main area, increases the thickness of the thinned area of the positive electrode edge, and reduces the distance between the thinned area of the positive electrode and the thinned area of the negative electrode edge, thereby effectively shortening the Li + Migration path; 3) At the same time, it can also effectively improve the thinning area Li +Diffusion coefficient, reduce the possibility of lithium plating in the negative electrode thinning area, and improve the safety performance of the battery. Compared with the conventional method of increasing NP ratio, it has cost and performance advantages. Specifically, on the one hand, there is no need to increase the amount of negative electrode coating to increase the NP ratio in the thinning area, which reduces the material cost; on the other hand, it can avoid the increase in electrolyte consumption caused by the formation of excess negative electrode material SEI film; and the present invention increases the NP ratio by reducing the positive electrode content in the thinning area, which does not reduce the positive electrode specific capacity, and also avoids the Li + In addition, the thinning trend of the thickness of the main area edge can be slowed down to reduce the Li+ between the positive electrode thinning area and the negative electrode thinning area. + Diffusion distance. The isatin anhydride in the conductive coating can neutralize the alkalinity on the surface of the positive electrode material particles and form a film on the positive electrode. The fluorinated anhydride can generate LiF, which improves conductivity, reduces internal resistance, and inhibits the formation of cracks within the positive electrode material particles during cycling, thereby improving circulation. Tris(trimethylsilyl)borate forms a stable and dense CEI film on the positive electrode, inhibiting the dissolution of the transition metal in the positive electrode material, improving the stability of the positive electrode material, and at the same time enhancing the charge transfer capacity of the electrode, thereby improving circulation.

[0034] The preparation method of the positive electrode sheet provided by the present invention has a simple process and low cost. The main area slurry and the conductive coating area slurry are simultaneously coated on the aluminum foil, which can slow down the thinning trend of the main area edge thickness and reduce the Li-ion gap between the positive electrode thinning area and the negative electrode thinning area. + The diffusion distance can be shortened and the NP ratio of the thinned area of the battery cell can be reduced by mutual dissolution, thereby improving the lithium deposition in the thinned area. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are 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 the structure of the positive electrode sheet in Example 1 of the present invention;

[0037] Reference numerals:

[0038] 1. Main body area; 2. Mixing area; 3. Conductive coating area. DETAILED DESCRIPTION

[0039] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0040] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0041] Example 1

[0042] This embodiment provides a positive electrode plate, such as Figure 1 As shown, it includes a main body area 1, a mixing area 2 and a conductive coating area 3. Its specific composition and preparation method are as follows:

[0043] S1: Lithium iron phosphate cathode material, polyvinylidene fluoride (PVDF) binder, and conductive carbon black (SP) are mixed in a mass ratio of 94.6:3.7:1.7, stirred thoroughly, and NMP is added to adjust the slurry viscosity. After thorough mixing, NMP is added to adjust the slurry viscosity to form a cathode slurry with a viscosity of 4500-8000 mPa·s and a solid content of 60%-70%. The cathode slurry is evenly coated on a 6μm aluminum foil with a double-sided coating weight of 50mg / cm 2 .

[0044] S2, polyvinylidene fluoride: 5-fluoroisatoic anhydride: tris(trimethylsilyl)borate: N-methylpyrrolidone in a mass ratio of 0.3:0.5:0.2:1, rotate at 20 rpm and 1500 rpm, and stir evenly for 40 minutes. After testing, the slurry viscosity is 3000 cP and the solid content is 35%.

[0045] S3, in the positive electrode coating process, use an extrusion coater to coat the slurry on a 13μm carbon-coated aluminum foil, then dry it in a coating oven at high temperature (drying temperature is between 90℃-120℃), and then roll and cut it to obtain a positive electrode sheet with a main body area thickness of 170μm, a mixing area width of 3mm, a conductive coating area width of 7mm and a thickness of 42μm.

[0046] Example 2

[0047] This embodiment provides a positive electrode plate. Compared with Example 1, the only difference is that the mass ratio of polymer binder: 5-fluoroindigo red anhydride: tris(trimethylsilyl)borate: N-methylpyrrolidone is 0.6:0.3:0.1:1.

[0048] Example 3

[0049] This embodiment provides a positive electrode plate. Compared with Example 1, the only difference is that the mass ratio of polymer binder: 5-fluoroindigo red anhydride: tris(trimethylsilyl)borate: N-methylpyrrolidone is 0.7:0.2:0.1:1.

[0050] Example 4

[0051] This embodiment provides a positive electrode plate, which is different from that of embodiment 1 only in that an equal mass of 6-fluoroisatidic anhydride is used instead of 5-fluoroisatidic anhydride.

[0052] Example 5

[0053] This embodiment provides a positive electrode plate. Compared with Example 1, the only difference is that the main area thickness of the obtained positive electrode plate is 170 μm, the width of the mixing area is 1 mm, and the width of the conductive coating area is 3 mm and the thickness is 17 μm.

[0054] Comparative Example 1

[0055] This comparative example provides a positive electrode sheet. The difference from Example 1 is that the lithium iron phosphate slurry is only coated on a 13 μm carbon-coated aluminum foil using an extrusion coater, without adding Li + Ion-conductive coating.

[0056] Test Case

[0057] Assembling the battery

[0058] The negative electrode was slurried in deionized water using artificial graphite particles: styrene-butadiene rubber: sodium carboxymethyl cellulose: conductive agent SP in a mass ratio of 96:1.7:1.3:1. The slurry viscosity was adjusted to 2500-4500 mPa·s and the solid content was 55-65%. The prepared slurry was evenly coated on 8μm copper foil with a double-sided coating weight of 25mg / cm 2 , and then through drying, rolling, die cutting, punching into negative electrode sheets.

[0059] The prepared positive and negative electrodes and separators are assembled together using a Z-shaped lamination process and packaged into soft-pack batteries. The cells are then baked, injected, formed, and sealed. The electrolyte is 1M LiPF6 dissolved in a mixture of ethylene carbonate and ethyl methyl carbonate (1:1 by volume).

[0060] Low temperature charging performance test

[0061] Discharge at room temperature with 1C constant current to 2.0V cutoff, then charge with 1C constant current and constant voltage to 3.8V, and cutoff at 0.05C, which is recorded as the initial charge capacity C0. Discharge at room temperature with 1C constant current to 2.0V cutoff, then place in a low-temperature test cabinet at -20℃ and leave for 8h; at -20℃, charge with 1C constant current and constant voltage to 3.8V, record the charge capacity C1, repeat the cycle 10 times, and record the charge capacity C2,...C10 of each cycle. Charging efficiency percentage (%) = Average(C1:C10) / C0×100%.

[0062] Cyclic performance test

[0063] -20℃, 1 / 3C charge, 1 / 3C discharge, repeated 200 cycles, cycle retention rate (%) = C200 / C1×100%.

[0064] Lithium deposition: After cycling, disassemble the battery and observe whether lithium deposition occurs at the edge of the electrode. See the table below for specific test results:

[0065] Table 1

[0066]

[0067] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A positive electrode plate, characterized in that: It includes a main body area, a mixing area and a conductive coating area. The mixing area is a mutually soluble area formed by the main body area material and the conductive coating area material during the coating process; the conductive coating area is located at the edges of both sides of the main body area; The conductive coating area is composed of a polymer binder, an isatin anhydride and tris(trimethylsilyl)borate in a mass ratio of (0.3-0.7): (0.2-0.5): (0.1-0.2).

2. The positive electrode sheet according to claim 1, characterized in that: The width of the conductive coating area is 3-7 mm.

3. The positive electrode sheet according to claim 1, characterized in that: The width of the mixing zone is 1.0-3.5 mm.

4. The positive electrode sheet according to claim 1, characterized in that: The thickness of the conductive coating area is 10-50% of the thickness of the main body area; And / or, the thickness of the main body region is 25-250 μm.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The polymer binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylate, polyimide, polyacrylonitrile, polysiloxane, and polyethylene oxide resin; And / or, the isatin anhydride includes at least one of 5-fluoroisatin anhydride and 6-fluoroisatin anhydride; And / or, the positive electrode active material in the main body region is lithium iron phosphate, a ternary lithium battery positive electrode material or a multi-element lithium battery positive electrode material.

6. A method for preparing a positive electrode sheet according to any one of claims 1 to 5, characterized in that: The steps include: S1, preparing the main area slurry; S2, dissolving a polymer binder, isatin anhydride and tris(trimethylsilyl)borate in an organic solvent to obtain a conductive coating slurry; S3, coating the main body region slurry and the conductive coating region slurry onto the current collector simultaneously, drying, rolling, and cutting to obtain the positive electrode sheet.

7. The method for preparing a positive electrode sheet according to claim 6, characterized in that: In step S2, the solid content of the conductive coating area slurry is 20-45%; And / or, the organic solvent includes N-methylpyrrolidone.

8. The method for preparing a positive electrode sheet according to claim 6, wherein: In step S3, the drying temperature is 90-120°C.

9. The method for preparing a positive electrode sheet according to claim 6, wherein: In step S1 , the main region slurry includes: a positive electrode active material, a conductive agent, a binder and a solvent.

10. A lithium ion battery, characterized in that: The invention comprises the positive electrode sheet according to any one of claims 1 to 5 or the positive electrode sheet prepared by the preparation method according to any one of claims 6 to 9.

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