Positive plate and battery

Abstract

The invention relates to the technical field of batteries, in particular to a positive plate and a battery. The positive plate comprises a positive current collector, the surface of at least one side of the positive current collector is provided with a plurality of recesses, the surface of the side, provided with the recesses, of the positive current collector is provided with a positive active layer, the diameter of each recess is 10-50 [mu] m, and the depth of each recess is smaller than 10 [mu] m; the surface roughness of the surface on the side having the plurality of depressions is represented by the arithmetic mean height Sa and the interface expansion area ratio Sdr: Sa is 0.5-1 [mu] m, and Sdr is 0.5-0.8. According to the positive plate disclosed by the invention, the positive current collector is provided with a plurality of recesses with specific sizes, the contact area between the positive active material and the positive current collector is larger, the binding power is better, the contact resistance is lower, and the electrochemical performance and the safety performance are better.

Description

[0001] This invention application is a divisional application of application number 2022103616537, filed on April 7, 2022, entitled "A positive current collector and its preparation method, a positive electrode sheet and its preparation method and a battery". Technical Field

[0002] This invention relates to the field of battery technology, and more specifically, to a positive electrode and a battery. Background Art

[0003] A lithium-ion battery mainly consists of five parts: a positive electrode, a negative electrode, a separator, an electrolyte, and a casing. The positive electrode's primary function is to output current during discharge and insert lithium ions that have migrated from the negative electrode; during charging, it receives current and extracts lithium ions to migrate to the negative electrode. To ensure the electrochemical activity and low internal resistance of the positive electrode, the coated and dried electrode needs to be rolled and compacted. Because the aluminum foil, as a carrier, is subjected to significant forces during coating and rolling, high-strength aluminum foil is currently used to prevent breakage. However, using high-hardness aluminum foil introduces another problem. Even after rolling, the aluminum foil remains difficult to deform, resulting in a small contact area between the active material and the foil, significantly increasing the contact resistance.

[0004] The existing solution involves coating a layer of carbon adhesive, composed of conductive carbon and a binder, onto a high-strength aluminum foil. This increases the contact between the active material and the aluminum foil, reduces contact resistance, and improves battery performance. However, this also introduces several problems: First, the carbon adhesive layer is thick, increasing the battery's volume and reducing its energy density. Second, during lithium battery cycling, the battery expands and contracts, and it sometimes operates at high temperatures, both of which can cause the carbon adhesive layer to potentially detach.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] One objective of this invention is to provide a positive electrode current collector to solve the problems of high contact resistance and poor adhesion caused by the small contact area between high-strength aluminum foil and positive electrode active material in the prior art.

[0007] Another objective of this invention is to provide a method for preparing the aforementioned positive electrode current collector, which is simple, easy to implement, and highly efficient.

[0008] Another objective of this invention is to provide a positive electrode sheet with a large contact area and good adhesion between the positive electrode active material and the positive electrode current collector.

[0009] Another objective of this invention is to provide a method for preparing a positive electrode sheet that is simple, easy to implement, and highly efficient.

[0010] Another object of the present invention is to provide a battery with excellent electrochemical performance and safety performance.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A positive electrode current collector, the positive electrode current collector comprising aluminum foil or composite aluminum foil, wherein at least one surface of the positive electrode current collector is a corroded surface; The hardness of the corroded surface is less than 30 kg / mm². 2 .

[0012] Preferably, the thickness of the positive electrode current collector is 5~16μm.

[0013] Preferably, the aluminum foil comprises H18 state aluminum foil.

[0014] Preferably, the composite aluminum foil includes a first aluminum foil and a second aluminum foil adhered to at least one side of the first aluminum foil, wherein the first aluminum foil and the second aluminum foil are in the H18 state.

[0015] Preferably, the thickness of the first aluminum foil is 4~6μm, and the thickness of the second aluminum foil is 5~7μm.

[0016] Preferably, the hardness of the corroded surface is 15~28 kg / mm². 2 .

[0017] The method for preparing the positive electrode current collector includes the following steps: At least one surface of the positive electrode current collector substrate is subjected to corrosion treatment by contacting it with an alkaline solution, followed by washing; the positive electrode current collector substrate includes an aluminum foil substrate or a composite aluminum foil substrate.

[0018] Preferably, the thickness of the aluminum foil substrate is 7~20μm.

[0019] Preferably, the method for preparing the composite aluminum foil substrate includes: coating at least one side surface of the first aluminum foil substrate with an adhesive, and then thermally bonding it with the second aluminum foil substrate; wherein the first aluminum foil substrate and the second aluminum foil substrate are both in the H18 state.

[0020] Preferably, the thickness of the first aluminum foil substrate is 5~7μm, and the thickness of the second aluminum foil is 6~8μm.

[0021] Preferably, the temperature of the thermal bonding is 90~100℃, and the pressure of the thermal bonding is 0.4~0.6MPa.

[0022] Preferably, after the thermal bonding, the mixture is left to stand for 140-160 hours before undergoing the corrosion treatment.

[0023] Preferably, the alkaline solution comprises a sodium hydroxide solution.

[0024] Preferably, the sodium hydroxide solution contains 8% to 12% sodium hydroxide by mass.

[0025] Preferably, the temperature of the corrosion treatment is 40~50℃, and the corrosion treatment time is 20~62s.

[0026] A positive electrode sheet includes the aforementioned positive current collector, wherein at least one side surface of the positive current collector has multiple depressions, the diameter of which is 10~50μm and the depth is less than 10μm.

[0027] A positive electrode active layer is disposed on the side surface of the positive electrode current collector with the depression.

[0028] Preferably, the surface roughness of the side surface with multiple depressions is expressed as the arithmetic mean height Sa and the ratio of the unfolded interface area Sdr, with Sa being 0.5~1 μm and Sdr being 0.5~0.8. Further, Sa is 0.5~0.97 μm and Sdr is 0.5~0.8; or Sa is 0.95~0.98 μm and Sdr is 0.71~0.75; or Sa is 0.85~0.97 μm and Sdr is 0.65~0.71.

[0029] Preferably, the positive electrode active layer comprises a positive electrode active material, a conductive agent, and a binder, wherein the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95~97):(1.5~2.5):(1~2.5).

[0030] Preferably, the positive electrode active material includes lithium cobalt oxide and / or lithium iron phosphate.

[0031] Preferably, the particle size of the positive electrode active material is 0.5~10μm, and the particle size of the conductive agent is 20nm~1μm.

[0032] Preferably, the compaction density of the positive electrode active layer is 4~4.2 g / m³. 3 .

[0033] The method for preparing the positive electrode includes the following steps: A slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent is coated onto at least one side of the positive electrode current collector, dried, and then compacted.

[0034] Preferably, the compaction pressure is 14.5 to 15.5 tons.

[0035] Preferably, the solid content of the mixed slurry is 64% to 70%.

[0036] Preferably, the mixed slurry is coated onto at least one side surface of the positive electrode current collector to form a slurry layer, and the areal density of the slurry layer is 185~195 g / m³. 2 .

[0037] A battery comprising the aforementioned positive electrode.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The positive electrode current collector of the present invention, by setting a specific corrosion surface, can ensure the high strength of the current collector, while increasing the contact area with the positive electrode active material, reducing the contact resistance, reducing the internal resistance of the battery, and improving the adhesion between the positive electrode active material and the aluminum foil.

[0039] (2) The method for preparing the positive current collector of the present invention is simple, easy and efficient. It can be achieved by using an alkaline solution to corrode and clean the surface of at least one side of the current collector.

[0040] (3) In the positive electrode sheet of the present invention, the positive electrode current collector has multiple depressions of a specific size, the contact area between the positive electrode active material and the positive electrode current collector is larger, and the adhesion is better.

[0041] (4) The method for preparing the positive electrode sheet of the present invention is simple, easy and efficient, by coating the positive electrode slurry onto at least one side of the positive electrode current collector and drying and compacting it.

[0042] (5) The battery of the present invention has excellent electrochemical performance and safety performance. Attached Figure Description

[0043] 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.

[0044] Figure 1 This is a cross-sectional SEM image of the positive electrode sheet in Embodiment 7 of the present invention; Figure 2 This is an SEM image of the surface of the positive electrode current collector after the active material on the surface of the positive electrode sheet in Embodiment 7 of the present invention has been removed; Figure 3 This is a cross-sectional SEM image of the positive electrode sheet in Comparative Example 1 of the present invention. Detailed Implementation

[0045] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0046] According to one aspect of the present invention, the present invention relates to a positive electrode current collector, the positive electrode current collector comprising aluminum foil or composite aluminum foil, wherein at least one surface of the positive electrode current collector is a corroded surface; The hardness of the corroded surface is less than 30 kg / mm². 2 .

[0047] The positive electrode current collector of the present invention, by setting a specific etched surface, can increase the contact area with the positive electrode active material while ensuring the strength of the current collector, thereby reducing the contact resistance and the internal resistance of the battery; it can also improve the adhesion between the positive electrode active material and the aluminum foil. In the positive electrode sheet obtained using the positive electrode current collector of the present invention, the positive electrode current collector has multiple indentations of a specific size, resulting in a larger contact area and better adhesion between the positive electrode active material and the positive electrode current collector. Specifically, the surface roughness of the side surface with multiple indentations is expressed as the arithmetic mean height Sa and the interfacial unfolded area ratio Sdr: Sa is 0.5~1μm, and Sdr is 0.5~0.8.

[0048] In one embodiment, Sa includes, but is not limited to, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm or 1.5μm.

[0049] In one implementation, Sdr includes, but is not limited to, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, or 1.2.

[0050] In one embodiment, the hardness of the corroded surface includes, but is not limited to, 5 kg / mm². 2 7Kg / mm 2 10Kg / mm 2 11Kg / mm 2 12Kg / mm 2 13Kg / mm 2 14Kg / mm 2 15Kg / mm 2 16Kg / mm 2 17Kg / mm 2 18Kg / mm 2 20Kg / mm 2 21Kg / mm2 22Kg / mm 2 23Kg / mm 2 24Kg / mm 2 25Kg / mm 2 26Kg / mm 2 27Kg / mm 2 28Kg / mm 2 Or 29Kg / mm 2 This invention achieves this by setting the surface hardness of the positive electrode current collector to be less than or equal to 30 kg / mm². 2 This ensures the hardness of the current collector, preventing strip breakage during later rolling, while also causing deformation and increasing the contact area with the positive electrode active material.

[0051] In one embodiment, the thickness of the positive electrode current collector is 5-16 μm. In another embodiment, the thickness of the positive electrode current collector includes, but is not limited to, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, or 16.5 μm.

[0052] In one embodiment, the composite aluminum foil includes a first aluminum foil and a second aluminum foil adhered to at least one surface of the first aluminum foil, wherein the first aluminum foil and the second aluminum foil are both in the H18 state. In one embodiment, the thickness of the first aluminum foil is 4-6 μm, and the thickness of the second aluminum foil is 5-7 μm. In another embodiment, the thickness of the first aluminum foil includes, but is not limited to, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5 μm, 5.1 μm, 5.1 μm, 5.3 μm, 5.5 μm, 5.6 μm, 5.8 μm, or 5.9 μm. In one embodiment, the thickness of the second aluminum foil includes, but is not limited to, 5.2 μm, 5.5 μm, 5.6 μm, 5.9 μm, 6 μm, 6.2 μm, 6.5 μm, 6.7 μm, or 6.9 μm.

[0053] In one embodiment, the hardness of the corroded surface is 15~28 kg / mm². 2 .

[0054] According to another aspect of the present invention, the present invention also relates to a method for preparing the aforementioned positive electrode current collector, comprising the following steps: At least one surface of the positive electrode current collector substrate is subjected to corrosion treatment by contacting it with an alkaline solution, followed by washing; the positive electrode current collector substrate includes an aluminum foil substrate or a composite aluminum foil substrate.

[0055] Alkali reacts chemically with aluminum to produce aluminates and hydrogen gas. During this process, the aluminum foil surface corrodes and undergoes hydrogen embrittlement, significantly reducing its surface hardness. Based on this mechanism, this invention uses an alkaline solution to corrode at least one side of the positive electrode current collector substrate, thereby forming a corroded surface and reducing the surface hardness of the positive electrode current collector. This method is simple and easy to implement.

[0056] In one embodiment, the thickness of the aluminum foil substrate is 7~20μm. In another embodiment, the thickness of the aluminum foil substrate includes, but is not limited to, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 19.5μm.

[0057] In one embodiment, the method for preparing the composite aluminum foil substrate includes: coating at least one surface of a first aluminum foil substrate with an adhesive, and then thermally bonding it with a second aluminum foil substrate; the first aluminum foil substrate and the second aluminum foil substrate are both in the H18 state. In one embodiment, the thickness of the first aluminum foil substrate is 5-7 μm, and the thickness of the second aluminum foil is 6-8 μm. The thickness of the first aluminum foil substrate includes, but is not limited to, 5.2 μm, 5.5 μm, 6 μm, 6.2 μm, 6.5 μm, 6.7 μm, or 6.9 μm. The thickness of the second aluminum foil includes, but is not limited to, 6.2 μm, 6.5 μm, 6.7 μm, 7 μm, 7.2 μm, 7.5 μm, 7.7 μm, or 7.9 μm.

[0058] In one embodiment, the thermal bonding temperature is 90~100℃, and the thermal bonding pressure is 0.4~0.6MPa. In another embodiment, the thermal bonding temperature includes, but is not limited to, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, or 99℃. The thermal bonding pressure includes, but is not limited to, 0.42MPa, 0.45MPa, 0.47MPa, 0.5MPa, or 0.55MPa.

[0059] In one embodiment, the heat-bonded material is left to stand for 140-160 hours before undergoing the corrosion treatment. In another embodiment, the standing time after heat-bonding includes, but is not limited to, 141h, 142h, 143h, 144h, 145h, 146h, 147h, 148h, 149h, 150h, 151h, 152h, 153h, 154h, 155h, 156h, or 159h.

[0060] In one embodiment, the alkaline solution comprises a sodium hydroxide solution.

[0061] In one embodiment, the sodium hydroxide solution contains 8% to 12% sodium hydroxide by mass. The mass percentage of sodium hydroxide includes, but is not limited to, 8.2%, 8.5%, 8.6%, 8.8%, 9%, 9.5%, 10%, 10.5%, 11%, or 11.5%.

[0062] In one embodiment, the etching temperature is 40-50°C, and the etching time is 20-62 seconds. The etching temperature includes, but is not limited to, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, or 49°C. The etching time is 20 seconds, 22 seconds, 25 seconds, 27 seconds, 30 seconds, 31 seconds, 33 seconds, 35 seconds, 37 seconds, 40 seconds, 42 seconds, 45 seconds, 46 seconds, 48 ​​seconds, 50 seconds, 53 seconds, 55 seconds, 57 seconds, 59 seconds, or 60 seconds.

[0063] This invention achieves a corroded surface with the desired hardness and roughness by treating the surface with an alkaline solution of appropriate concentration and temperature for an appropriate time.

[0064] According to another aspect of the present invention, the present invention also relates to a positive electrode sheet, comprising the aforementioned positive current collector, wherein at least one side surface of the positive current collector has a plurality of recesses, the diameter of the recesses being 10~50μm and the depth being less than 10μm; A positive electrode active layer is disposed on the side surface of the positive electrode current collector with the depression.

[0065] The positive electrode sheet of the present invention can increase the contact area between the positive electrode active material and the positive electrode current collector, and reduce the internal resistance of the battery; the multiple recessed structures form an embedding effect, making the bond stronger and improving the adhesion between the positive electrode active material and the positive electrode current collector.

[0066] In one embodiment, the diameter of the recess includes, but is not limited to, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 27 μm, 30 μm, 32 μm, 35 μm, 37 μm, 40 μm, 42 μm, 45 μm, 46 μm, or 48 μm. The depth of the recess includes, but is not limited to, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or 9.5 μm.

[0067] In one embodiment, the surface roughness of the side surface with multiple depressions is expressed as an arithmetic mean height Sa and an interface unfolded area ratio Sdr, where Sa is 0.5~1 μm and Sdr is 0.5~0.8. Further, Sa is 0.5~0.97 μm and Sdr is 0.5~0.8; or Sa is 0.95~0.98 μm and Sdr is 0.71~0.75; or Sa is 0.85~0.97 μm and Sdr is 0.65~0.71.

[0068] In one embodiment, the arithmetic mean height Sa includes, but is not limited to, 0.951 μm, 0.955 μm, 0.958 μm, 0.959 μm, 0.96 μm, 0.965 μm, 0.968 μm, 0.97 μm, 0.972 μm, 0.975 μm, 0.977 μm, or 0.98 μm. The unfolded area ratio Sdr is 0.71, 0.712, 0.715, 0.717, 0.72, 0.723, 0.725, 0.727, 0.729, 0.73, 0.732, 0.735, 0.737, 0.74, 0.742, 0.745, 0.748, or 0.75.

[0069] In one embodiment, the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder, wherein the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95~97):(1.5~2.5):(1~2.5).

[0070] In one embodiment, the mass ratio of the positive electrode active material, the conductive agent, and the binder is 95:2.5:2.5, 96:2:2, or 97:1.5:1.5.

[0071] In one embodiment, the positive electrode active material includes lithium cobalt oxide and / or lithium iron phosphate.

[0072] In one embodiment, the particle size of the positive electrode active material is 0.5~10 μm, and the particle size of the conductive agent is 20 nm~1 μm. In another embodiment, the particle size of the positive electrode active material includes, but is not limited to, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm. The particle size of the conductive agent can be 20 nm, 50 nm, 100 nm, 500 nm, 800 nm, or 1 μm.

[0073] In one embodiment, the conductive agent comprises conductive carbon black.

[0074] In one embodiment, the adhesive comprises PVDF (polyvinylidene fluoride), such as PVDF HSV900.

[0075] In one embodiment, the compaction density of the positive electrode active layer is 4~4.2 g / m³. 3 The compaction density of the positive electrode active layer includes, but is not limited to, 4.1 g / m³. 3 4.12g / m 3 4.15g / m 3 4.17g / m 3 .

[0076] According to another aspect of the present invention, the present invention also relates to a method for preparing the aforementioned positive electrode sheet, comprising the following steps: The mixture of the positive electrode active material, conductive agent, binder and solvent is coated onto at least one side of the positive electrode current collector, dried and then compacted.

[0077] The method for preparing the positive electrode sheet of this invention is simple and easy to implement. During the compaction process, the surface hardness of the positive electrode current collector decreases, and the positive electrode active material squeezes the aluminum foil, causing the aluminum foil to deform and form a depression with a diameter of 10~50μm and a depth of less than 10μm; thereby increasing the contact area between the positive electrode active material and the positive electrode current collector.

[0078] In one embodiment, the compaction pressure is 14.5 to 15.5 tons. The compaction pressure includes, but is not limited to, 14.2 tons, 14.5 tons, 14.7 tons, 15 tons, 15.2 tons, or 15.4 tons.

[0079] In one embodiment, the solid content of the mixed slurry is 64% to 70%. The solid content of the mixed slurry includes, but is not limited to, 65%, 66%, 67%, 68%, or 69%.

[0080] In one embodiment, the solvent comprises N-methylpyrrolidone.

[0081] In one embodiment, the mixed slurry is coated onto at least one surface of the positive electrode current collector to form a slurry layer, the areal density of the slurry layer being 185~195 g / m³. 2 The areal density of the slurry layer includes, but is not limited to, 186 g / m³. 2 187g / m 2 188g / m 2 190g / m 2 192g / m 2 193 g / m 2 Or 194g / m 2 .

[0082] In one embodiment, the drying temperature is 95~105℃, and the drying time is 3.5~4.5h. In another embodiment, the drying temperature includes, but is not limited to, 96℃, 97℃, 98℃, 99℃, 100℃, 101℃, or 103℃. The drying time includes, but is not limited to, 3.7h, 4h, or 4.3h.

[0083] According to one aspect of the invention, the invention also relates to a battery comprising the aforementioned positive electrode.

[0084] The battery of this invention has excellent electrochemical performance and high safety performance.

[0085] The present invention will be further explained below with reference to specific embodiments and comparative examples.

[0086] In one embodiment, lithium cobalt oxide is selected from GEM Co., Ltd.

[0087] In one embodiment, the conductive carbon black Super P is selected from Timcal.

[0088] In one implementation, the PVDF HSV900 is selected from Arkema.

[0089] In one embodiment, the adhesive WB888 is selected from Wuxi Yuke Company.

[0090] In one embodiment, lithium iron phosphate is selected from Defang Nano.

[0091] The following explanation, in conjunction with specific embodiments and comparative examples, further clarifies the situation.

[0092] Example 1 A method for preparing a positive electrode current collector includes the following steps: Using 14μm H18 state aluminum foil as the substrate, the sample was immersed in a sodium hydroxide solution for 25 seconds. The sodium hydroxide solution contained 10% solute by mass and was at a temperature of 45°C. The sample was then quickly removed and rinsed with distilled water.

[0093] Example 2 A method for preparing a positive current collector, except that H18 state aluminum foil is immersed in sodium hydroxide solution for 20 seconds, other conditions are the same as in Example 1.

[0094] Example 3 A method for preparing a positive current collector, except that H18 state aluminum foil is immersed in sodium hydroxide solution for 40 seconds, other conditions are the same as in Example 1.

[0095] Example 4 A method for preparing a positive electrode current collector includes the following steps: (a) Preparation of composite aluminum foil: an adhesive was coated on a 5μm H18 state aluminum foil and dried. After drying, the adhesive layer was 1.5μm thick. The adhesive was WB888 glue. The aluminum foil was thermally laminated with a 6μm H18 state aluminum foil at a temperature of 95℃ and a pressure of 0.5MPa. The settling time after lamination was 150 hours. (b) Surface corrosion of composite aluminum foil: The composite aluminum foil obtained in step (a) is immersed in sodium hydroxide solution for 60 seconds, wherein the mass content of sodium hydroxide solution is 10% and the temperature is 45°C; then it is quickly removed and rinsed with distilled water.

[0096] Example 5 A method for preparing a positive current collector, except that the composite aluminum foil is immersed in sodium hydroxide solution for 20 seconds, is the same as in Example 2.

[0097] Example 6 A method for preparing a positive current collector, except that the composite aluminum foil is immersed in sodium hydroxide solution for 40 seconds, is the same as in Example 2.

[0098] Example 7 A method for preparing a positive electrode sheet includes the following steps: (a) The positive electrode active material, conductive agent and binder are added to N-methylpyrrolidone in a mass ratio of 96:2:2 and stirred evenly to form a positive electrode slurry. The solid content of the slurry is 65%. The positive electrode active material is lithium cobalt oxide, the conductive agent is conductive carbon black Super P, and the binder is PVDF HSV900. (b) The positive electrode slurry obtained in step (a) is uniformly coated on one side surface of the positive electrode current collector in Example 1, with an areal density of 190 g / m³. 2 After vacuum drying at 100°C for 4 hours, the above-mentioned positive electrode slurry was coated on the other side of the positive electrode current collector and then vacuum dried. The dried positive electrode sheet was then rolled at a pressure of 15 tons, and the compacted density after rolling was 4.1 g / m³. 3 .

[0099] The cross-sectional SEM image of the positive electrode in this embodiment is as follows: Figure 1 As shown. The SEM image of the positive electrode current collector surface after removing the active material from the positive electrode sheet in this embodiment is shown below. Figure 2 As shown.

[0100] Example 8 A method for preparing a positive electrode sheet, except that the positive electrode current collector obtained in Example 2 is used, and the other conditions are the same as in Example 7.

[0101] Example 9 A method for preparing a positive electrode sheet, except that the positive electrode current collector obtained in Example 3 is used, and the other conditions are the same as in Example 7.

[0102] Example 10 A method for preparing a positive electrode sheet, except that the positive electrode current collector obtained in Example 4 is used, and the other conditions are the same as in Example 7.

[0103] Example 11 A method for preparing a positive electrode sheet, except that the positive electrode current collector obtained in Example 5 is used, and the other conditions are the same as in Example 7.

[0104] Example 12 A method for preparing a positive electrode sheet, except that the positive electrode current collector obtained in Example 6 is used, and the other conditions are the same as in Example 7.

[0105] Example 13 A method for preparing a positive electrode sheet, wherein the positive electrode active material is lithium iron phosphate and the coating surface density is 200 g / m². 2 The density after rolling is 2.40 g / m³. 3 Other conditions are the same as in Example 7.

[0106] Example 14 A method for preparing a positive electrode sheet, wherein the positive electrode active material is lithium iron phosphate and the coating surface density is 200 g / m². 2 The density after rolling is 2.40 g / m³. 3 Other conditions are the same as in Example 10.

[0107] Example 15 A method for preparing a positive electrode sheet, except that the H18 state aluminum foil is subjected to single-sided etching treatment; a slurry is coated on the etched surface, and other conditions are the same as in Example 7.

[0108] Comparative Example 1 A positive current collector is a 12μm H18 state aluminum foil.

[0109] A method for preparing a positive electrode sheet, except that the above-mentioned 12μm H18 state aluminum foil is directly used as the current collector, and other conditions are the same as in Example 7.

[0110] The cross-sectional SEM image of the positive electrode in this comparative example is shown below. Figure 3 As shown.

[0111] Comparative Example 2 A positive current collector was prepared according to step (a) of Example 4.

[0112] A method for preparing a positive electrode sheet, except that the positive current collector used in this comparative example is used, and other conditions are the same as in Example 7.

[0113] Comparative Example 3 A method for preparing a positive electrode sheet, except that the positive electrode active material is lithium iron phosphate, and other conditions are the same as those in Comparative Example 2.

[0114] Experimental Example I. Hardness Test The thickness, Vickers hardness, and surface roughness of the positive electrode current collectors obtained in Examples 1, 4, and Comparative Examples 1-2 were tested, and the test results are shown in Table 1.

[0115] Roughness testing: According to ISO 25178, the surface properties of the positive electrode current collector were tested using the Keyence VK-X3000 shape measurement laser microscope system. The arithmetic mean height Sa and the interface unfolded area ratio Sdr were measured. The interface unfolded area ratio Sdr indicates how much the unfolded area of ​​the defined region increased relative to the area of ​​the defined region. Sdr is 0 for a completely flat surface. If the surface is tilted, Sdr will be larger.

[0116] Sa=1 / A·∫ A ∫|Z(x,y)|dxdy.

[0117] .

[0118] Table 1. Test results of thickness and hardness of the positive electrode current collector.

[0119] As shown in Table 1, this invention, by using alkaline solution to etch the positive electrode current collector and defining specific etching conditions, can impart a surface with specific hardness and roughness to the positive electrode current collector. This facilitates deformation during subsequent compaction with the slurry, increases the contact area with the positive electrode active material, improves adhesion, and reduces the battery's internal resistance. In Comparative Examples 1 and 2, the current collectors were not subjected to alkaline solution etching, resulting in higher surface hardness. After rolling, the positive electrode active material and the high-strength positive electrode current collector were difficult to deform, leading to a very small contact area between the active material and the current collector, which significantly increases the contact resistance.

[0120] II. Testing the peeling force of the positive electrode sheet The positive electrode sheets obtained in Examples 7, 10, 13, Comparative Example 2, and Comparative Example 3 were subjected to peel strength tests, using the same methods as those in patent application CN201811570558.8. The test results are shown in Table 2.

[0121] Table 2 Test results of positive electrode peeling force

[0122] As shown in Table 2, the positive electrode sheet obtained by the method of the present invention undergoes deformation during the rolling process due to the compression of the positive electrode active material onto the surface of the positive electrode current collector, resulting in an interlocking effect and thus improving the adhesion between the positive electrode active material and the current collector. The peel force between the positive electrode active material and the current collector of the present invention is above 22 N / cm, while that of Comparative Example 2 is 14.6 N / cm and that of Comparative Example 3 is 13.5 N / cm, which are far lower than the peel force of the embodiments of the present invention.

[0123] III. Testing of surface roughness of the positive electrode The positive electrode sheets obtained in Examples 7, 10, 13, 14, and Comparative Examples 2 and 3 were immersed in N-methylpyrrolidone and then the surface material was washed off. SEM observation was performed to measure the surface depression dimensions. The arithmetic mean height Sa and the interfacial spread area ratio Sdr of the positive electrode current collector surface after removing the surface active layer were measured. The results are shown in Table 3.

[0124] Table 3 Test results of positive electrode peeling force

[0125] As shown in Table 3, the method of the present invention creates a depression on the surface of the positive electrode current collector, which increases the contact area with the positive electrode active material and improves the adhesion.

[0126] IV. Composite Solvent Immersion Experiment The positive electrode sheets obtained in Examples 7-14 and Comparative Examples 1-3 were soaked in a composite solvent and ultrasonically treated for 15 minutes. The detachment of the active material layer was observed. The composite solvent was a mixture of EC (ethylene carbonate), PC (propylene carbonate) and DMC (dimethyl carbonate), with a mass ratio of EC:PC:DMC of 1:1:3.

[0127] The results show that the positive electrode sheet of the present invention did not detach after being soaked in the composite solvent. However, the positive electrode sheets of Comparative Examples 1 to 3 all experienced detachment of the positive electrode active layer.

[0128] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 positive electrode plate, characterized in that, The device includes a positive current collector, wherein at least one side surface of the positive current collector has multiple depressions, and a positive active layer is disposed on the side surface of the positive current collector having the depressions, wherein the diameter of the depressions is 10~50μm and the depth is less than 10μm. The surface roughness of the side surface with multiple depressions is expressed as the arithmetic mean height Sa and the ratio of the unfolded interface area Sdr: Sa is 0.5~1μm, and Sdr is 0.5~0.

8. The method for preparing the positive electrode sheet includes the following steps: providing a current collector raw material having at least one etched surface; coating a mixed slurry of positive electrode active material, conductive agent, binder, and solvent onto at least one etched surface of the current collector raw material, drying it, and then compacting it; the coating surface density of the mixed slurry is 185~195 g / m³. 2 The drying temperature is 95–105°C, and the compaction pressure is 14.5–15.5 tons. The hardness of the corroded surface is less than 30 kg / mm². 2 The current collector raw material includes aluminum foil or composite aluminum foil, the aluminum foil including H18 state aluminum foil; the composite aluminum foil includes a first aluminum foil and a second aluminum foil adhered to at least one side of the first aluminum foil, the first aluminum foil and the second aluminum foil being H18 state respectively; The method for preparing the current collector raw material having at least one corroded surface includes: contacting at least one side of the current collector raw material with an alkaline solution for corrosion treatment, followed by washing; the alkaline solution includes a sodium hydroxide solution; the sodium hydroxide solution contains 8% to 12% sodium hydroxide by mass; the temperature of the corrosion treatment is 40 to 50°C, and the corrosion treatment time is 20 to 62 seconds.

2. The positive electrode sheet according to claim 1, characterized in that, The surface roughness of the side surface with multiple depressions is represented by the arithmetic mean height Sa and the ratio of the unfolded interface area Sdr, and satisfies any one of the following characteristics: (1) Sa is 0.5~0.97μm, Sdr is 0.5~0.8; (2) Sa is 0.95~0.98μm, Sdr is 0.71~0.75; (3) Sa is 0.85~0.97μm, and Sdr is 0.65~0.

71.

3. The positive electrode sheet according to claim 1, characterized in that, The hardness of the corroded surface is 15~28 kg / mm². 2 .

4. The positive electrode sheet according to claim 1, characterized in that, It has at least one of the following characteristics: (1) The thickness of the positive electrode current collector is 5~16μm; (2) The thickness of the current collector raw material is 7~20μm.

5. The positive electrode sheet according to claim 1, characterized in that, The method for preparing the composite aluminum foil includes: coating at least one side surface of the first aluminum foil with an adhesive, and then thermally bonding it with the second aluminum foil; Preferably, the thickness of the first aluminum foil is 5~7μm, and the thickness of the second aluminum foil is 6~8μm.

6. The positive electrode sheet according to claim 5, characterized in that, The temperature of the thermal bonding is 90~100℃, and the pressure of the thermal bonding is 0.4~0.6MPa; Preferably, after the thermal bonding, the mixture is left to stand for 140-160 hours before undergoing the corrosion treatment.

7. The positive electrode sheet according to claim 1, characterized in that, In the positive electrode active layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (95~97):(1.5~2.5):(1~2.5). Preferably, the positive electrode active material includes lithium cobalt oxide and / or lithium iron phosphate.

8. The positive electrode sheet according to claim 7, characterized in that, The particle size of the positive electrode active material is 0.5~10μm, and the particle size of the conductive agent is 20nm~1μm; Preferably, the compaction density of the positive electrode active layer is 4~4.2 g / m³. 3 .

9. The positive electrode sheet according to claim 1, characterized in that, The solid content of the mixed slurry is 64% to 70%.

10. A battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1 to 9.

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