Positive electrode current collector, secondary battery, and electric device

Abstract

The application discloses a positive electrode current collector, a secondary battery and an electric device, and belongs to the technical field of batteries. The positive electrode current collector comprises a base layer and a coating layer arranged on at least one surface of the base layer, wherein the coating layer comprises a binder, and a structural formula of the binder contains a carboxyl group and at least one amide group. The positive electrode current collector satisfies 9%≤△T 300 -△T 450 ≤22%; wherein, △T 300 is a peak value of a TG spectrum of the positive electrode current collector at 300 DEG C; and △T 450 is a peak value of the TG spectrum of the positive electrode current collector at 450 DEG C. The positive electrode current collector disclosed by the application effectively improves the cycle performance of the secondary battery and reduces the DCR.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive current collector, a secondary battery, and an electrical device. Background Technology

[0002] Secondary batteries have outstanding advantages such as high energy density, high power density, long service life and no memory effect, and have been widely used in consumer electronics, home appliances, aerospace, electric vehicles and other fields.

[0003] Cathode active materials, especially lithium iron phosphate, are widely used in lithium-ion secondary batteries. They are widely used in the preparation of secondary batteries because of their characteristics such as large discharge capacity, high safety, low price and no environmental pollution. However, their poor conductivity has seriously hindered their practical application, resulting in insufficient cycle performance.

[0004] Therefore, this application is submitted. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the existing technology and provide a positive current collector, a secondary battery and an electrical device, which can effectively improve the cycle performance of the secondary battery and reduce the DCR.

[0006] To achieve the above objectives, a first aspect of this application provides a positive electrode current collector, the positive electrode current collector comprising a substrate layer and a coating disposed on at least one surface of the substrate layer, the coating comprising an adhesive having a structural formula containing a carboxyl group and at least one amide group;

[0007] The positive electrode current collector satisfies: 9% ≤ ΔT 300 -△T 450 ≤22%;

[0008] Among them, △T 300 The peak value of the TG spectrum of the positive electrode current collector at 300℃;

[0009] △T 450 The peak value of the TG spectrum of the positive electrode current collector at 450℃.

[0010] As an embodiment of this application, the adhesive comprises the structural formula shown in Formula I:

[0011]

[0012] In Equation I, y:x = (5~25):(75~95), 20000≤x≤30000.

[0013] As an embodiment of this application, the adhesive accounts for 45% to 50% of the coating by mass.

[0014] As an embodiment of this application, the coating further includes a water-resistant agent, which includes at least one of calcium hydroxide, calcium oxide, sodium hydroxide, calcium chloride, and silica gel.

[0015] As an embodiment of this application, the water-repellent agent has a mass percentage content of 2% to 10% in the coating.

[0016] As an embodiment of this application, the mass ratio of the adhesive to the anti-absorption agent is (6-10):1.

[0017] As an embodiment of this application, the coating further includes a conductive agent, wherein the conductive agent has a mass percentage content of 40% to 45% in the coating.

[0018] As an embodiment of this application, the thickness of the coating is 0.5 μm to 5 μm.

[0019] As an embodiment of this application, the diaphragm resistance of the positive current collector is 55mΩ to 185mΩ.

[0020] A second aspect of this application provides a secondary battery including a positive electrode sheet, the positive electrode sheet including the positive current collector described above and a positive active material layer disposed on at least one surface of the positive current collector.

[0021] As an embodiment of this application, the bonding force of the positive electrode sheet is 17.5 N / m to 28 N / m.

[0022] A third aspect of this application provides an electrical device including the aforementioned secondary battery.

[0023] The beneficial effects of this application are as follows: the positive current collector described in this application includes a substrate layer and a coating disposed on at least one surface of the substrate layer, wherein the coating contains a binder with a structure containing carboxyl groups and at least one amide group, and satisfies: 10% ≤ ΔT 300 -△T 450 ≤20%; It can effectively reduce heat and weight loss, improve the thermal stability of the positive electrode current collector, and the binder can hydrate with the conductive agent to form double hydrogen bonds, effectively improving the adhesion between the positive electrode current collector and the positive electrode active material layer, better connecting the substrate layer and the positive electrode active material, effectively improving the adhesion and conductivity of the positive electrode sheet, while effectively reducing the contact resistance between the undercoat layer and the positive electrode active material layer, effectively improving the cycle performance of the secondary battery and reducing DCR. Attached Figure Description

[0024] Figure 1 The TG spectra are for Example 1, Comparative Examples 1 and 2.

[0025] Figure 2 The images show the film resistance diagrams for Examples 1, 1, and 2.

[0026] Figure 3 The adhesive force diagrams are for Example 1, Comparative Examples 1 and 2.

[0027] Figure 4 The diagram shows the cyclic performance of Example 1, Comparative Examples 1 and 2.

[0028] Figure 5 The DCR diagrams are for Example 1, Comparative Examples 1 and 2. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0031] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0032] In this application, there are no particular restrictions on the specific stirring, mixing, ball milling, and rolling processes. Those skilled in the art can select appropriate specific stirring, mixing, ball milling, and rolling processes according to actual needs.

[0033] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this invention are commercially available, and the components and raw materials used in each parallel experiment are the same.

[0034] This application provides a positive electrode current collector, which includes a substrate layer and a coating disposed on at least one surface of the substrate layer. The coating includes an adhesive, and the adhesive has a structural formula containing a carboxyl group and at least one amide group.

[0035] The positive electrode current collector satisfies: 9% ≤ ΔT300 -△T 450 ≤22%, for example, can be 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, or a range of any two of these values;

[0036] Among them, △T 300 The peak value of the TG spectrum of the positive electrode current collector at 300℃;

[0037] △T 450 The peak value of the TG spectrum of the positive electrode current collector at 450℃.

[0038] The positive current collector described in this application includes a substrate layer and a coating disposed on at least one surface of the substrate layer. The coating contains a binder with a structure containing carboxyl groups and at least one amide group, and satisfies: 10% ≤ ΔT 300 -△T 450 ≤20%; It can effectively reduce heat and weight loss, improve the thermal stability of the positive electrode current collector, and the binder can hydrate with the conductive agent to form double hydrogen bonds, effectively improving the adhesion between the positive electrode current collector and the positive electrode active material, better connecting the substrate layer and the positive electrode active material layer, effectively improving the adhesion and conductivity of the positive electrode sheet, and effectively reducing the contact resistance between the undercoating layer and the positive electrode active material layer, effectively improving the cycle performance of the secondary battery and reducing DCR.

[0039] In one embodiment, the adhesive has the structural formula shown in Formula I:

[0040]

[0041] In Equation I, y:x = (5~25):(75~95), 20000≤x≤30000.

[0042] This application uses a binder as shown in Formula I, whose molecular structure contains a carboxyl group and at least one amide group. It can not only form hydrogen bonds with the hydroxyl groups on the surface of the conductive agent, but also form intermolecular hydrogen bonds, effectively improving the adhesion between the positive electrode current collector and the positive electrode active material. At the same time, it effectively reduces thermal weight loss, improves the thermal stability of the positive electrode current collector, improves the safety of the secondary battery, effectively improves the cycle performance of the secondary battery, and reduces DCR.

[0043] In the binder shown in Formula I, the ratio of glycine amide segments to acrylic acid segments is (5-25):(75-95), and x is 20000-30000. The binder not only has extremely high thermal stability, reduces the thermal weight loss of the positive electrode current collector, and improves the safety of the secondary battery, but also provides better adhesion between the matrix layer and the positive electrode active material layer, further improving the binder and conductivity, thereby further improving cycle performance and reducing DCR.

[0044] In one embodiment, the positive current collector satisfies: 13% ≤ ΔT 300 -△T 450 ≤20%.

[0045] In one embodiment, the adhesive content in the coating is 45% to 50% by mass, for example, it can be a range of 45%, 46%, 47%, 48%, 49%, 50%, or any two of these values. By controlling the adhesive content in the coating within this range, ΔT is adjusted. 300 -△T 450 The value is adjusted to avoid excessive thermal and gravitational loss of the positive current collector, improve safety, and maintain good adhesion while improving conductivity.

[0046] In one embodiment, the coating further includes a water-resistant agent, which includes at least one of calcium hydroxide, calcium oxide, sodium hydroxide, calcium chloride, and silica gel.

[0047] In one embodiment, the anti-water-absorbing agent has a mass percentage content of 2% to 10% in the coating, for example, it can be a range of 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any two of these values. By controlling the amount of anti-water-absorbing agent within this range, the moisture content of the electrode is reduced and the battery performance is improved.

[0048] In one embodiment, the mass ratio of the adhesive to the anti-absorption agent is (6-10):1, for example, it can be 6:1, 7:1, 8:1, 9:1, 10:1 or any two of these values. By controlling the mass ratio of the adhesive to the anti-absorption agent within this range, both the adhesion ability of the electrode sheet and the moisture content are taken into account.

[0049] In one embodiment, the coating further includes a conductive agent, the conductive agent having a mass percentage content of 40% to 45% in the coating, for example, it can be 40%, 41%, 42%, 43%, 44%, 45% or any two of these values. By controlling the content of the conductive agent within this range, the conductive agent can better form hydrogen bonds with the adhesive, thereby improving the adhesion.

[0050] In one embodiment, the conductive agent comprises at least one of conductive carbon black, conductive graphite, carbon nanotubes, and graphene.

[0051] In one embodiment, the thickness of the coating is 0.5 μm to 5 μm, for example, it can be 0.5 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any two of these values.

[0052] In one embodiment, the thickness of the coating is 1 μm to 3 μm.

[0053] In one embodiment, the thickness of the substrate layer is 12 μm to 15 μm, for example, it can be 12 μm, 13 μm, 14 μm, 15 μm or any two of these values.

[0054] In one embodiment, the type of substrate layer is not particularly limited, and it can be any known material suitable for use as a substrate layer.

[0055] In one embodiment, the substrate layer includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0056] In one embodiment, the substrate layer is a metallic material. In one embodiment, the positive current collector is aluminum.

[0057] There are no particular restrictions on the form of the substrate layer. When the substrate layer is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the substrate layer is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0058] In one embodiment, the diaphragm resistance of the positive current collector is 55mΩ to 185mΩ, for example, it can be 55mΩ, 65mΩ, 75mΩ, 85mΩ, 95mΩ, 105mΩ, 115mΩ, 125mΩ, 135mΩ, 145mΩ, 155mΩ, 165mΩ, 175mΩ, 185mΩ or any two of these values.

[0059] In one embodiment, the adhesive is prepared by:

[0060] The pH of the polyacrylic acid solution was adjusted to 5.5-6 using a pH adjuster. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were added and stirred until homogeneous. Then, glycine hydrochloride was added and reacted to obtain the adhesive.

[0061] The reaction principle of the adhesive is as follows:

[0062]

[0063] In one embodiment, the mass concentration of the polyacrylic acid solution is 0.1% to 10%, for example, it can be 0.1%, 0.2%, 0.5%, 1%, 2%, 4%, 5%, 6%, 8%, 10%, or any two of these values.

[0064] In one embodiment, the mass ratio of the polyacrylic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, and N-hydroxysuccinimide is 100:(15-25):(10-15), for example, it can be 100:15:10, 100:18:12, 100:20:15, 100:25:10, or any range of two of these values.

[0065] In one embodiment, the molar ratio of polyacrylic acid to glycine hydrochloride is (8-12):1, for example, it can be 8:1, 9:1, 10:1, 11:1, 12:1 or any range of two of these values.

[0066] In one embodiment, the pH adjuster includes at least one of sodium hydroxide solution, potassium hydroxide solution, and ammonia water.

[0067] In one embodiment, the reaction temperature is 20 to 40°C, for example, a range of 20°C, 22°C, 25°C, 28°C, 30°C, 32°C, 35°C, 38°C, 40°C, or any two of these values.

[0068] In one embodiment, the reaction time is 12 to 72 hours, for example, it can be 12 hours, 16 hours, 20 hours, 24 hours, 30 hours, 36 hours, 40 hours, 48 ​​hours, 52 hours, 60 hours, 64 hours, 68 hours, 72 hours or any two of these values.

[0069] One embodiment of this application provides a secondary battery, the secondary battery having a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive current collector includes the positive current collector described above.

[0070] In one embodiment, the bonding strength of the positive electrode sheet is 17.5 N / m to 28 N / m. The bonding strength of the positive electrode sheet is the bonding strength between the positive active material layer and the positive current collector.

[0071] In one embodiment, the positive electrode sheet includes a positive electrode active material, which may be selected from sodium-iron composite oxides, sodium-cobalt composite oxides, sodium-manganese composite oxides, sodium-nickel composite oxides, sodium-nickel-titanium composite oxides, sodium-nickel-manganese composite oxides, sodium-iron-manganese composite oxides, sodium-nickel-cobalt-manganese composite oxides, sodium-iron phosphate compounds, sodium-manganese phosphate compounds, sodium-cobalt phosphate compounds, lithium nickel-cobalt-manganese oxides, lithium-containing phosphates, etc. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0072] In one embodiment, the secondary battery includes a positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer comprising a positive active material comprising carbon-coated lithium iron phosphate, the positive current collector comprising a substrate layer and a coating disposed on at least one surface of the substrate layer, the coating comprising a binder having a structural formula containing a carboxyl group and at least two amide groups.

[0073] The binder has at least two amide groups in its structural formula, which allows the binder molecular chains to form double hydrogen bonds. It can also form double hydrogen bonds by hydration with hydroxyl groups on the surface of the lithium iron phosphate carbon layer and the conductive agent, thereby improving the adhesion between the current collector and the positive electrode active material and improving the electrochemical performance of the positive electrode.

[0074] In one embodiment, the secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material.

[0075] In this application, there are no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector, etc.

[0076] In one embodiment, the negative electrode active material can be natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, or spinel-structured lithium titanate Li4Ti5O. 12 At least one of Li-Al alloys and metallic lithium.

[0077] In the secondary battery mentioned in this application, a separator is usually provided between the positive and negative electrodes to prevent short circuits. There are no particular restrictions on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application.

[0078] In one embodiment, the diaphragm comprises a porous sheet-like or nonwoven material with excellent liquid retention properties. Materials for resin or glass fiber diaphragms include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone.

[0079] In one embodiment, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the diaphragm described above can be used alone or in any combination.

[0080] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0081] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0082] In some embodiments, the type of electrolyte is not specifically limited. The electrolyte includes an electrolyte salt and an organic solvent, and the specific types of the electrolyte salt and organic solvent are not specifically limited and can be selected according to actual needs. The electrolyte may also include additives, and the type of additives is not particularly limited. These additives can be film-forming additives for the positive and / or negative electrodes, or additives that can improve certain battery performance, such as additives that improve the battery's high or low temperature performance.

[0083] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0084] One embodiment of this application provides an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.

[0085] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0086] The present application is further illustrated below with specific embodiments:

[0087] Example 1

[0088] A method for preparing a secondary battery includes the following steps:

[0089] (1) Preparation of adhesive: 1g of polyacrylic acid was added to water to prepare a 1% polyacrylic acid solution. The pH was adjusted to 5.8 with sodium hydroxide. 0.2g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 0.12g of N-hydroxysuccinimide were added and stirred evenly. 0.23g of glycine hydrochloride was added. After concentration, dialyzing with a dialysis bag, and drying, the adhesive (hereinafter referred to as PAA-GA) was obtained.

[0090] (2) Preparation of positive electrode sheet: Conductive carbon black SP, binder from step (1) and calcium hydroxide are mixed in a mass ratio of 47:50:5 to prepare a coating slurry; take an aluminum foil with a thickness of 13μm, coat the coating slurry on the surface of the aluminum foil, dry it to form a positive current collector;

[0091] Lithium iron phosphate, conductive carbon black SP, polyvinylidene fluoride, and solvent N-methylpyrrolidone were mixed in a mass ratio of 8:1:1 to form a uniform electrode slurry. The slurry was then uniformly coated onto the positive current collector, dried at 110°C, and rolled to obtain the positive electrode sheet.

[0092] (3) Preparation of negative electrode sheet: Graphite, polyvinylidene fluoride, conductive carbon black SP and solvent N-methylpyrrolidone are mixed in a mass ratio of 8:1:1 to form a uniform electrode slurry. The slurry is then uniformly coated on a copper foil with a thickness of 8μm. After drying at 110℃, it is rolled to obtain a negative electrode active material layer.

[0093] (4) Assembly of the secondary battery: The separator is a polypropylene porous membrane; dimethyl carbonate and ethylene carbonate are mixed together in a mass ratio of 4:6, and lithium hexafluorophosphate is added to it as the electrolyte solution, wherein the molar concentration of lithium hexafluorophosphate is 1 mol / L. The positive electrode, negative electrode, separator and electrolyte solution are assembled into a coin cell to obtain the secondary battery.

[0094] The specific parameters of the positive current collector in this embodiment are shown in Table 1.

[0095] Examples 2-5

[0096] The difference between Examples 2-5 and Example 1 is that the amount of PAA-GA added is changed in Examples 2-5.

[0097] Examples 6-10

[0098] The difference between Examples 6-10 and Example 1 is that the amount of calcium hydroxide added is changed in Examples 6-10.

[0099] Examples 11-13, Comparative Examples 3-4

[0100] The difference between Examples 11-13 and Comparative Examples 3-4 and Example 1 is that the ratio of x and y in the PAA-GA structural formula is adjusted by changing the amount of glycine hydrochloride added.

[0101] Examples 14-17

[0102] The difference between Examples 14-17 and Example 1 is that Examples 14-17 use polyacrylic acid with different molecular weights, thereby changing the x in the PAA-GA structural formula.

[0103] Examples 18-20

[0104] The difference between Examples 18-20 and Example 1 is that the thickness of the coating is changed in Examples 18-20.

[0105] Comparative Example 1

[0106] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses polyacrylic acid (hereinafter referred to as PAA) as a binder.

[0107] Comparative Example 2

[0108] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses SBR as the binder.

[0109] Table 1

[0110]

[0111]

[0112] Test case

[0113] 1. TG spectrum: "Reference standard: GB / T 27761-2011 Test method for weight loss and residue of thermogravimetric analyzer, test temperature: 30~500℃, 10℃ / min, upper limit temperature: 800℃; test atmosphere: nitrogen / air; test crucible: aluminum crucible / alumina crucible."

[0114] The TG test spectra of Example 1, Comparative Examples 1 and 2 are as follows: Figure 1 As shown.

[0115] 2. Diaphragm resistance of the positive current collector: Test area: 15.4025 mm² 2 Triggering pressure: 0.4t; Sampling time: 10s; Test parallel samples: 10; First, test the membrane resistance values ​​r1, r2, and r3 under no-load conditions 3 times. Then, take the membrane resistance values ​​R1 to R10 at 10 different locations on the electrode. Calculate the membrane resistance value = (R1 + R2... + R10) / 10 - (r1 + r2 + r3) / 3.

[0116] Among them, the diaphragm resistors of Example 1, Comparative Examples 1 and 2 are as follows: Figure 2 As shown.

[0117] 3. Adhesion force: Sample size: 40mm*400mm; Sensor: 50N; Default peel length: 150mm; Test settings: Full scale 50N; Load limit 40N; Stroke limit 150mm; Stroke speed 50mm / min; Change point: 150mm; Data processing settings: Initial stroke 40mm, End stroke 120mm; Upper limit 50N, Lower limit 0N; Test 3 parallel samples; Record the average tensile force F1, F2, F3 (unit: N) of the tensile testing machine within the stroke of 40~120mm, Adhesion force = (F1+F2+F3) / 0.04 / 3 (unit: N / m).

[0118] The adhesive strength of Examples 1, 1, and 2 is as follows: Figure 3 As shown.

[0119] 4. Cycling performance: 45℃ cycle performance test: At 45℃, the battery is charged and discharged at a 1C / 1C rate within the range of 2.5~3.8V. The discharge specific capacity of the battery in the first cycle and the discharge specific capacity after 500 cycles are recorded. The capacity retention rate after 500 cycles is calculated as follows: discharge specific capacity after 500 cycles = discharge specific capacity after 500 cycles / discharge specific capacity after the first cycle * 100%.

[0120] The cyclic performance of Examples 1, 1, and 2 is as follows: Figure 4 As shown.

[0121] 5. DCR: At 25℃, adjust the battery to 10%, 50%, and 90% SOC, and charge it with a 4C current for 10 seconds. Record the voltage rise ΔV and the current I, and calculate DCR: DCR = ΔV / I.

[0122] Among them, the DCR of Example 1, Comparative Examples 1 and 2 are as follows Figure 5 As shown.

[0123] Table 2

[0124]

[0125]

[0126] As can be seen from Table 2, the positive electrode current collector described in this application can significantly improve adhesion and conductivity, thereby significantly reducing membrane resistance, improving adhesion, and thus significantly improving the cycle performance of the secondary battery and reducing DCR.

[0127] As can be seen from the comparison of Example 1 and Comparative Examples 1-2, the adhesive described in this application can significantly improve the adhesion and conductivity, thereby significantly reducing the membrane resistance, improving the adhesion, and thus significantly improving the cycle performance of the secondary battery and reducing the DCR.

[0128] Comparing Example 1 with Comparative Examples 3-4, it can be seen that this application achieves better results by controlling 9% ≤ ΔT. 300 -△T 450 ≤22%, further improving cycle performance and reducing DCR.

[0129] As can be seen from the comparison of Examples 1 to 5, this application can balance the adhesive force and electrochemical performance, reduce processing risks, and avoid delamination during processing by controlling the content of the adhesive in the coating to 45% to 50%.

[0130] Comparing Examples 1, 6-10, it can be seen that this application further reduces DCR by controlling the content of anti-water absorption agent in the coating to 2%-10%.

[0131] Comparing Example 1 with Examples 14-17, it can be seen that by controlling x in the adhesive structural formula to be 20000-30000, this application effectively improves the adhesion, enhances the cycle performance of the secondary battery, and reduces DCR.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A positive electrode current collector, characterized in that, The positive current collector includes a substrate layer and a coating disposed on at least one surface of the substrate layer. The coating includes an adhesive, the adhesive having a structural formula containing a carboxyl group and at least one amide group, and the adhesive comprising the structural formula shown in Formula I. Formula I In Equation I, y:x = (5~25):(75~95), 20000≤x≤30000; The positive electrode current collector satisfies: 9% ≤ ΔT 300 -△T 450 ≤22%; Among them, △T 300 The peak value of the TG spectrum of the positive electrode current collector at 300℃; △T 450 The peak value of the TG spectrum of the positive electrode current collector at 450℃.

2. The positive current collector according to claim 1, characterized in that, The adhesive comprises 45% to 50% by mass in the coating.

3. The positive electrode current collector according to claim 1, characterized in that, The coating also includes a water-resistant agent, which includes at least one of calcium hydroxide, calcium oxide, sodium hydroxide, calcium chloride, and silica gel.

4. The positive electrode current collector according to claim 3, characterized in that, The water-absorbing agent has a mass percentage content of 2% to 10% in the coating.

5. The positive electrode current collector according to claim 3, characterized in that, The mass ratio of the adhesive to the water-resistant agent is (6~10):

1.

6. The positive electrode current collector according to claim 1, characterized in that, The coating also includes a conductive agent, which has a mass percentage of 40% to 45% in the coating.

7. The positive current collector according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The thickness of the coating is 0.5μm~5μm; (2) The diaphragm resistance of the positive current collector is 55mΩ~185mΩ.

8. A secondary battery, characterized in that, It includes a positive electrode sheet, wherein the positive electrode sheet includes a positive current collector as described in any one of claims 1 to 7 and a positive active material layer disposed on at least one surface of the positive current collector.

9. The secondary battery according to claim 8, characterized in that, The bonding strength of the positive electrode sheet is 17.5 N / m to 28 N / m.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 8 or 9.

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