A high-safety composite positive electrode current collector, its preparation method and application

Abstract

This invention belongs to the field of battery material technology, and relates to a high-safety composite positive electrode current collector, its preparation method, and its application. This positive electrode current collector effectively addresses or mitigates cell safety issues. It includes an aluminum foil substrate and a composite layer disposed on the upper and lower surfaces of the aluminum foil substrate. The composite layer comprises a conductive carbon layer and a mica coating, with the conductive carbon layer disposed between the aluminum foil surface and the mica coating. The mica coating is composed of arrayed dot-matrix units. The positive electrode sheet prepared using this current collector exhibits excellent performance, and its application in batteries can significantly improve their safety. This invention prepares the positive electrode current collector through aluminum foil substrate pretreatment, preparation of conductive slurry, coating of conductive carbon layer, carbon-coated aluminum foil pretreatment, preparation of mica insulating slurry, and coating of mica coating. This method utilizes readily available raw materials, has a simple process flow, and is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a high-safety composite positive electrode current collector, its preparation method and application. Background Technology

[0002] Lithium-ion batteries (LIBs) play a crucial role in modern society, with widespread applications in portable electronics, electric vehicles, and smart grids. However, safety concerns have consistently hindered their further development. In practical applications, even millisecond-level transient short circuits within the battery cell can trigger uncontrollable thermal runaway.

[0003] Improving needle penetration by coating aluminum foil (positive electrode current collector) is an important technological direction in the field of lithium-ion battery safety. It aims to reduce the contact between aluminum foil and negative electrode active material during needle penetration by coating the aluminum foil surface with a specific coating, thereby reducing the risk of short circuit and the possibility of thermal runaway.

[0004] Patent document CN113381057A discloses a high-safety lithium-ion battery and its preparation method. The high-safety lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector, a conductive carbon layer disposed on the surface of the positive current collector, a positive electrode slurry layer disposed on the surface of the conductive decarburized layer, and a ceramic material layer disposed on the surface of the positive electrode slurry layer. The negative electrode includes a negative current collector, a conductive carbon layer disposed on the surface of the negative current collector, and a negative electrode slurry layer disposed on the surface of the conductive decarburized layer. By increasing or decreasing the coating structure on the current collector, the safety performance of the battery, especially the needle penetration effect, is improved.

[0005] Patent document CN104332658A discloses a high-safety lithium-ion battery, which includes a packaging shell, a positive electrode, a negative electrode, an electrolyte, and a separator between the positive and negative electrode sheets disposed within the packaging shell. The positive electrode includes a positive current collector and a positive electrode coating area, wherein the positive electrode coating area is coated with a positive active material layer on the positive current collector. The negative electrode includes a negative current collector and a negative electrode coating area, wherein the negative electrode coating area is coated with a negative active material layer on the negative current collector. The positive current collector is provided with a positive electrode blank area, and the end of the positive electrode coating area is coated with a ceramic coating. When the battery is abused, the safety hazards caused by the large energy generated by the direct short circuit between the positive and negative electrode sheets inside the battery are avoided.

[0006] Patent document TW202033447A discloses a method for preparing a carbon conductive coating for use on current collectors in lithium-ion batteries. The method includes providing carbon material dissolved and dispersed in a solvent, a binder, a conductive agent, and additives; then, the binder, conductive agent, and additives are sequentially mixed by ball milling and ultrasonic treatment to form a conductive slurry. A coupling agent is added and mixed with the conductive slurry. A conductive carbon-coated current collector is prepared by coating the conductive slurry onto a copper foil.

[0007] Patent document CN108493455A discloses a multifunctional lithium battery current collector and its preparation method. The current collector includes a metal foil and a multifunctional material layer covering the upper and lower surfaces of the metal foil. The metal foil is aluminum foil, copper foil, carbon-coated aluminum foil, or carbon-coated copper foil. The multifunctional material layer is composed of at least one polymer material and at least one conductive material. This multifunctional lithium battery current collector features low contact resistance and high bonding strength with the active material of the lithium battery, effectively improving the cycle performance of the lithium battery. It also enables active thermal management of the lithium battery, effectively preventing thermal runaway and thus improving the safety performance of the lithium battery.

[0008] In summary, the current mainstream current collector coating technologies fall into two categories: conductive coatings and insulating coatings. Conductive coatings involve applying a carbon-based material to the current collector surface, but they do not specifically address or mitigate safety issues. Insulating coatings typically involve applying a ceramic or polymer-based insulating material to the current collector surface to form a barrier layer. However, ceramic coatings are double insulators of both ions and electrons, significantly increasing interfacial impedance, leading to increased internal resistance, decreased power, and reduced fast-charging performance. Polymer coatings generally have poor conductivity and are temperature-resistant below 300°C, potentially melting, decomposing, or even producing flammable gases in the early stages of thermal runaway, which is detrimental to battery safety. Summary of the Invention

[0009] Based on this, the purpose of this invention is to provide a high-safety composite positive electrode current collector, which is a composite coated positive electrode current collector based on a combination of a conductive carbon layer and an insulating coating, and has the effect of specifically solving or mitigating cell safety issues. This current collector uses a carbon coating layer as a conductive coating on the upper and lower surfaces of an aluminum foil, which can reduce the internal resistance of the electrode and enhance rate performance. Simultaneously, a mica coating with a dotted array arrangement is coated on the surface of the conductive coating, providing high-temperature resistance and insulation. The mica coating provides reliable physical insulation, preventing large-scale internal short circuits caused by direct contact between the positive and negative electrodes. Furthermore, the dotted array coating design, rather than a full-coverage coating, ensures lithium-ion conduction with almost no increase in ion migration resistance, and has virtually no impact on the electrical performance of the cell.

[0010] This invention also provides a method for preparing a high-safety composite positive current collector, which uses readily available raw materials, has a simple process flow, and is easy to mass-produce.

[0011] The present invention also provides a high-safety battery, wherein the positive electrode uses a high-safety composite positive electrode current collector, and the battery has high thermal stability.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] The present invention provides a high-safety composite positive current collector, comprising an aluminum foil substrate and a composite layer disposed on the upper and lower surfaces of the aluminum foil substrate. The composite layer comprises a conductive carbon layer and a mica coating. The conductive carbon layer is disposed between the aluminum foil surface and the mica coating. The mica coating is composed of a lattice unit distributed in an array.

[0014] Furthermore, the aluminum foil has a thickness of 12~16μm, the conductive carbon layer has a thickness of 0.5~3μm, and the mica coating has a thickness of 0.5~3μm; the lattice units in the mica coating include circular lattices with a diameter of 1~5μm and a distribution density of 40~60% of the area of ​​the conductive carbon layer.

[0015] Furthermore, the conductive carbon layer contains a conductive agent, which includes any one or more of conductive carbon black (SP), carbon nanotubes (CNTs), graphene (Gr), and conductive graphite (KS-6), wherein the conductive carbon black (SP) is preferably acetylene black (AB) and / or Ketjen black (KB).

[0016] Furthermore, the mica coating contains mica particles with a median particle size D50 of 1~8μm. Preferably, the mica particles comprise flaky mica powder.

[0017] This invention further provides a method for preparing the above-mentioned high-safety composite positive current collector, comprising the following steps:

[0018] S1, Aluminum foil substrate pretreatment: The aluminum foil to be coated is first cleaned with alkaline solution and deionized water in sequence, and then dried and surface treated to obtain the pretreated aluminum foil substrate.

[0019] S2, Coating a conductive carbon layer: A conductive paste containing a conductive agent is coated on the upper and lower surfaces of the pretreated aluminum foil substrate described in S1, and after drying, a carbon-coated aluminum foil is obtained.

[0020] S3, Pretreatment of carbon-coated aluminum foil: The carbon-coated aluminum foil described in S2 is subjected to surface treatment to obtain pretreated carbon-coated aluminum foil.

[0021] S4, Coating with mica coating: Mica insulating slurry containing mica particles is coated on the upper and lower surfaces of the pretreated carbon-coated aluminum foil described in S3, and after drying, a high-safety composite positive current collector is obtained.

[0022] Further, the cleaning method using alkaline solution and deionized water described in S1 is as follows: a chemical treatment is performed using a sodium carbonate or sodium hydroxide solution with a mass concentration of 5-10 wt%. This chemical treatment involves spraying at 50-55°C for 10-30 seconds, followed by rinsing with deionized water until the conductivity is ≤10 μS / cm. Preferably, the aluminum foil to be coated is dried after cleaning until no moisture residue remains on its surface.

[0023] Furthermore, the surface treatment described in S1 includes corona treatment, with a frequency of 15±2 kHz and a voltage of 15±2 kV; the surface treatment described in S3 includes corona treatment, with a frequency of 5±1 kHz and a voltage of 5±1 kV.

[0024] Further, the conductive slurry in S2 includes a conductive agent with a mass fraction of 1-10 wt%, a first binder with a mass fraction of 0.5-4 wt%, a first solvent with a mass fraction of 90-98 wt%, and a first dispersant with a mass fraction of 0-1.5 wt%. After mixing the conductive agent, the first binder, the first solvent, and the first dispersant, the mixture is first pre-dispersed for 0.5-1 hour, and then accelerated to high-speed dispersion for 1-5 hours to obtain the conductive slurry. The power of the high-speed dispersion is 3-5 times that of the pre-dispersion power. Preferably, the power of different dispersion machines is different during dispersion. Taking a maximum power of 50 Hz as an example, the pre-dispersion power is 10 ± 1 Hz, and the accelerated dispersion power is 40 ± 1 Hz.

[0025] Further, the conductive paste is uniformly coated onto the upper and lower surfaces of the pretreated aluminum foil substrate described in S1 using a wet coating process. After coating, the substrate is dried by segmented heating to obtain a carbon-coated aluminum foil. The wet coating process includes slot extrusion coating. Preferably, the segmented heating process is divided into three stages: the first stage is 85±1℃, the second stage is 105±1℃, and the third stage is 110±1℃.

[0026] Further, the first adhesive includes acrylic acid, styrene-butadiene rubber, or polyvinylidene fluoride; the first solvent includes deionized water, ethanol, or N-methylpyrrolidone; and the first dispersant includes polyvinylpyrrolidone (PVP), hydroxypropyltrimethylammonium chloride, chitosan, or polyethylene oxide.

[0027] Further, the mica insulating slurry described in S4 includes 30-50 wt% mica particles, 50-68 wt% second solvent, 0.5-1.0 wt% second binder, and 0-1.5 wt% second dispersant; the mica particles, second solvent, second binder, and second dispersant are ground to obtain a mica insulating slurry with a median particle size D50 of 0.5-1.0 μm; preferably, the grinding includes ball milling, and the ball-to-material ratio during ball milling is 1:1.

[0028] Further, the mica insulating slurry is uniformly coated onto the upper and lower surfaces of the pretreated carbon-coated aluminum foil described in S3 using a dot matrix coating method. After coating, a high-safety composite positive current collector is obtained after segmented heating and drying. The dot matrix coating method includes gravure printing. Preferably, the segmented heating is divided into three stages: the first stage is 85±1℃, the second stage is 105±1℃, and the third stage is 110±1℃.

[0029] Further, the second solvent includes deionized water, the second binder includes any one or more of styrene-butadiene rubber, polyacrylic acid, acrylic polymer, sodium carboxymethyl cellulose and waterborne polyurethane, and the second dispersant includes polyacrylate, phosphate salt, polyvinylpyrrolidone or polyacrylic acid.

[0030] The present invention further provides an application of the above-mentioned high-safety composite positive electrode current collector, which is applied to a high-safety battery. The high-safety battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode includes the high-safety composite positive electrode current collector.

[0031] The beneficial effects of this invention are:

[0032] 1. The high-safety composite positive current collector provided by the present invention is a composite coating positive current collector based on the combination of conductive carbon layer and insulating coating (i.e. mica coating), which has the effect of specifically solving or mitigating cell safety problems.

[0033] 2. The high-safety composite positive current collector provided by this invention uses a carbon coating layer as a conductive coating on the upper and lower surfaces of an aluminum foil, which can reduce the internal resistance of the electrode and enhance rate performance, mainly solving the electrical performance problem. Simultaneously, a mica coating with a dotted array arrangement is coated on the conductive coating surface, providing high-temperature resistance and insulation, mainly addressing safety issues. The mica coating provides reliable physical insulation, preventing large-scale internal short circuits caused by direct contact between the positive current collector and the negative electrode. Furthermore, the dotted coating design, rather than a full-coverage coating, ensures lithium-ion conduction with almost no increase in ion migration resistance, having virtually no impact on the cell's electrical performance.

[0034] 3. The high-safety battery provided by the present invention is a positive electrode sheet obtained by coating a positive electrode slurry with a high-safety composite positive electrode current collector as a substrate. The positive electrode sheet has high safety. When the positive electrode sheet is applied to the battery, it can effectively enhance the thermal stability of the battery and improve its safety.

[0035] 4. The method for preparing the high-safety composite positive current collector provided by the present invention involves pretreatment of an aluminum foil substrate, coating with a conductive carbon layer, pretreatment of carbon-coated aluminum foil, and coating with a mica coating to obtain the positive current collector. The raw materials are readily available, the process is simple, and it is easy to mass-produce. Attached Figure Description

[0036] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Appendix Figure 1 The diagram shows the structure of the high-safety composite positive electrode current collector prepared according to the present invention, wherein Figure A is a cross-sectional view and Figure B is a surface view;

[0038] Appendix Figure 2 This is a schematic diagram of the preparation process of the conductive carbon layer in the preparation of the high-safety composite positive electrode current collector of the present invention;

[0039] Appendix Figure 3 This is a schematic diagram of the mica coating preparation process for preparing the high-safety composite positive current collector according to the present invention;

[0040] Appendix Figure 4 This is a summary table of the parameters and performance of the positive electrode current collectors prepared in the embodiments and comparative examples of the present invention;

[0041] Appendix Figure 5 The resistivity and battery internal resistance of the positive current collector electrodes prepared using the embodiments and comparative examples of the present invention are compared and analyzed. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All mentioned embodiments are implemented based on the technical solutions of the present invention, and detailed implementation processes are given. However, it should be stated that the scope of protection of the present invention is not limited to the following embodiments.

[0043] The following embodiments provide detailed implementation procedures for the technical solutions of the present invention. Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0044] like Figure 1 As shown, the high-safety composite current collector prepared in this embodiment of the invention includes an aluminum foil substrate and a composite layer disposed on the upper and lower surfaces of the aluminum foil substrate. The composite layer includes a conductive carbon layer and a mica coating, with the conductive carbon layer disposed between the aluminum foil surface and the mica coating. Figure 1 (Figure A in the diagram); the mica coating consists of arrayed lattice units ( Figure 1 (Figure B in the diagram). Figure 2 and Figure 3 The preparation process involves first pretreating the aluminum foil substrate, then preparing the conductive paste and the mica insulating paste, and finally coating the positive electrode current collector with two layers: the first conductive carbon layer is coated on the side close to the positive electrode current collector, and the second mica coating is coated on the conductive carbon layer in a dot matrix pattern.

[0045] The embodiment of this invention completes the cell (i.e., battery) preparation through the following steps: preparation of a high-safety composite current collector, coating of positive and negative electrode slurries, roll pressing and slitting, cell winding, welding and assembly, baking, electrolyte injection 1, activation, formation, aging, electrolyte injection 2, sealing, and capacity testing. Then, the embodiment is evaluated and assessed.

[0046] Example 1

[0047] 1. The preparation of a high-safety composite positive electrode current collector mainly includes the following steps:

[0048] (1) Preparation of conductive paste: SP, CNTs, PVDF, NMP, and PVP were pre-dispersed in a high-speed disperser (model: Hongyun-20L) at a speed of 10 Hz for 1 h, and then dispersed at a high speed of 40 Hz for 5 h until a stable conductive paste that is not prone to settling was formed. The mass fraction ratio of SP:CNTs:PVDF:NMP:PVP was 0.5%:6.5%:1.5%:91%:0.5%.

[0049] (2) Aluminum foil substrate pretreatment: The aluminum foil (12μm) to be coated is cleaned (chemically treated), dried, and corona treated. Chemical treatment is performed using a 5% sodium carbonate solution, i.e., spraying at 55℃ for 30s, followed by rinsing with deionized water until the conductivity is ≤10μS / cm. The aluminum foil is dried using a blower until no moisture remains on the surface. The dried aluminum foil is then quickly passed through a high-frequency, high-voltage (15kHz, 15kV) electrode for corona treatment, thus completing the aluminum foil substrate pretreatment.

[0050] (3) Coating with conductive carbon layer and completing pretreatment: The conductive paste prepared in step (1) is uniformly coated onto the surface of aluminum foil through slit extrusion, with a coating thickness of about 1 μm. The carbon-coated aluminum foil after double-sided coating is subjected to segmented heating and drying (divided into three segments: the first segment at 85°C, the second segment at 105°C, and the third segment at 110°C), and then rapidly passed through a high-frequency high-voltage (5 kHz, 5 kV) electrode for flexible corona treatment, thus completing the pretreatment of the carbon-coated aluminum foil substrate.

[0051] (4) Preparation of mica insulating slurry: Flake mica powder (D50 about 8μm), deionized water, SBR and dispersant are fed into a ball mill (ball-to-powder ratio of 1:1) and ground until the slurry is uniform and stable and the particle size D50 is 0.5μm. The mass fraction ratio of flake mica powder:deionized water:SBR:PVP is 35%:0.6%:63.4%:1%.

[0052] (5) Mica Coating: A custom gravure roller is used, and the roller surface is laser-engraved to form the required circular dot matrix. The pit depth is 0.5 μm, the diameter is 1 μm, and the distribution density is 40% (area ratio). The gravure plate is immersed in the slurry tank, and the excess slurry is scraped off with a scraper, leaving only a fixed amount of slurry in the pits. When the roller comes into contact with the carbon-coated aluminum foil, the slurry in the pits is transferred to the aluminum foil surface under pressure to form a discrete mica dot matrix. The double-sided coated composite current collector is then subjected to segmented heating and drying to complete the preparation of the high-safety composite current collector.

[0053] 2. The preparation of high-safety batteries mainly includes the following steps:

[0054] (1) Preparation of positive electrode slurry: The positive electrode active material lithium iron phosphate (LFP), binder polyvinylidene fluoride (PVDF), conductive agent carbon black (SP) and conductive agent carbon nanotubes (CNTs) are dispersed in N-methylpyrrolidone (NMP) in a mass ratio of 96.0:2.0:1.2:0.8 to obtain the positive electrode slurry;

[0055] (2) Preparation of negative electrode slurry: The negative electrode active material graphite (Gr), conductive agent carbon black (SP), carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are dispersed in deionized water at a mass ratio of 96.0:1.0:1.3:1.7 to obtain the negative electrode slurry.

[0056] (3) Electrode preparation: The positive electrode slurry is uniformly and stably coated on both sides of the prepared high-safety composite current collector, and the negative electrode slurry is uniformly and stably coated on both sides of the copper foil. The surface density of the positive electrode coating is 180 g / m². 2 The negative electrode coating surface density is 70 g / m². 2 After drying, rolling, and slitting, positive and negative electrode sheets are obtained. The compacted density of the positive electrode sheet is 2.35 g / m³.3 The compaction density of the negative electrode sheet is 1.45 g / m³. 3 .

[0057] (4) Battery preparation: The positive and negative electrode sheets and the separator are wound, and then the tabs are flattened, welded and assembled, the cell is baked, the electrolyte is injected for the first time (135g of electrolyte is injected, and the mass fraction ratio of the electrolyte formula is EC:DMC:LiPF6:VC:PS=23:57:10:5:5), activated, formed, aged, injected for the second time (15g of electrolyte is injected, and the mass fraction ratio of the electrolyte formula is EC:DMC:LiPF6:VC:PS=23:57:10:5:5), sealed, and capacity testing are performed to obtain the 60130 lithium-ion cylindrical battery used in this invention.

[0058] Example 2

[0059] A custom gravure roller has a surface laser-engraved with a desired circular dot matrix. The pits are 0.5 μm deep, 1 μm in diameter, and have a distribution density of 45% (area percentage). Everything else is the same as in Example 1.

[0060] Example 3

[0061] A custom gravure roller has a surface laser-engraved with a desired circular dot matrix. The pits are 0.5 μm deep, 1 μm in diameter, and have a distribution density of 50% (area percentage). Everything else is the same as in Example 1.

[0062] Example 4

[0063] A custom gravure roller has a surface laser-engraved with a circular dot matrix, the pits being 0.5 μm deep, 1 μm in diameter, and distributed at a density of 55% (area percentage). Everything else is the same as in Example 1.

[0064] Example 5

[0065] A custom gravure roller is used, with the roller surface laser-engraved to form the required circular dot matrix. The pits are 0.5 μm deep, 1 μm in diameter, and distributed at a density of 60% (area percentage). Everything else is the same as in Example 1.

[0066] Example 6

[0067] A custom gravure roller is used, with the roller surface laser-engraved to form the required circular dot matrix. The pits are 1 μm deep and 1 μm in diameter, with a distribution density of 40% (area percentage). Everything else is the same as in Example 1.

[0068] Example 7

[0069] A custom gravure roller is used, with the roller surface laser-engraved to form the required circular dot matrix. The pits are 1.5 μm deep, 1 μm in diameter, and distributed at a density of 40% (area percentage). Everything else is the same as in Example 1.

[0070] Example 8

[0071] A custom gravure roller has a surface laser-engraved with a circular dot matrix, the pits being 2.0 μm deep, 1 μm in diameter, and distributed at a density of 40% (area percentage). Everything else is the same as in Example 1.

[0072] Example 9

[0073] A custom gravure roller has a surface laser-engraved with a circular dot matrix, the pits being 2.5 μm deep, 1 μm in diameter, and distributed at a density of 40% (area percentage). Everything else is the same as in Example 1.

[0074] Example 10

[0075] A custom gravure roller is used, with the roller surface laser-engraved to form the required circular dot matrix. The pits are 3.0 μm deep, 1 μm in diameter, and distributed at a density of 40% (area percentage). Everything else is the same as in Example 1.

[0076] Example 11

[0077] A custom gravure roller has a surface laser-engraved with a circular dot matrix. The dot depth is 0.5 μm, the diameter is 2.0 μm, and the distribution density is 40% (area percentage). Everything else is the same as in Example 1.

[0078] Example 12

[0079] A custom gravure roller has a surface laser-engraved with a circular dot matrix. The dot depth is 0.5 μm, the diameter is 3.0 μm, and the distribution density is 40% (area percentage). Everything else is the same as in Example 1.

[0080] Example 13

[0081] A custom gravure roller has a surface laser-engraved with a circular dot matrix. The dot depth is 0.5 μm, the diameter is 4.0 μm, and the distribution density is 40% (area percentage). Everything else is the same as in Example 1.

[0082] Example 14

[0083] A custom gravure roller has a surface laser-engraved with a circular dot matrix. The dot depth is 0.5 μm, the diameter is 5.0 μm, and the distribution density is 40% (area percentage). Everything else is the same as in Example 1.

[0084] Comparative Example 1

[0085] Preparation of positive electrode current collectors containing only a conductive carbon layer and their application in battery fabrication

[0086] The difference between this comparative example and Example 1 is that: (1) the coating thickness of the conductive carbon layer is about 2 μm. (2) no mica coating was applied.

[0087] Comparative Example 2

[0088] The difference between this comparative example and Example 1 is that: (1) the coating thickness of the conductive carbon layer is about 3 μm. (2) no mica coating was applied.

[0089] Comparative Example 3

[0090] The difference between this comparative example and Example 1 is that: (1) the coating thickness of the conductive carbon layer is about 4 μm. (2) no mica coating was applied.

[0091] Implementation effect analysis

[0092] The positive electrode sheets and batteries prepared in Examples 1-14 and Comparative Examples 1-3 were subjected to the following tests: (1) Test method for electrode internal resistance: The resistivity of the electrode was tested at 25 MPa using an electrode resistance meter. (2) Test method for battery internal resistance: The AC internal resistance (ACR) of the battery was tested using a battery AC internal resistance tester. (3) Test method for battery thermal runaway performance: The fully charged battery was heated according to the method in UL / 9540A2019 until the cell experienced thermal runaway.

[0093] Test results are as follows Figure 4 and Figure 5 As shown. Figure 4 For the various modified experimental items in the examples and comparative examples, a gradient comparison of four major experimental items was carried out, namely the area ratio of the insulating layer (i.e., mica coating) to the conductive layer (i.e., conductive carbon layer), the thickness of the insulating layer, the diameter of a single coated circle (i.e., lattice unit) of the insulating layer, and the thickness of a single conductive layer. Figure 5 The paper provides comparative data on electrode resistance and battery internal resistance in various embodiments and comparative examples, which shows that the two are strongly correlated. As the electrode resistance increases, the cell internal resistance also increases. The increase in electrode internal resistance changes with the increase in the thickness and area ratio of the insulating layer. The experimental results show that the embodiments provide the optimal solution for balancing conductivity and insulation performance. Figure 4The results show that the thermal runaway experiments of the batteries in all embodiments and comparative examples passed. However, in the comparative examples, the battery surface temperature rose to over 300°C. This is because no insulating layer was coated in the comparative examples. During thermal runaway, the presence of only a conductive layer was insufficient to effectively prevent the internal short circuit caused by the contact of the positive and negative electrodes, resulting in a huge heat burst. In the embodiments, increasing the coating area and thickness of the mica insulating layer significantly and effectively improved the thermal runaway effect, reducing the battery surface temperature to below 100°C.

[0094] In summary, the high-safety composite positive electrode current collector prepared in the examples achieves "functional partitioning" and "physical isolation" in its design. The first conductive carbon layer coated in the current collector has the following advantages: (1) Since CNTs form a three-dimensional conductive network, the transmission of electrons between the current collector and the active material is greatly improved, which can reduce the internal resistance of the electrode and improve the rate performance. (2) The uniform conductive layer helps the current distribution of the electrode to be more uniform, reduces local overcharging / over-discharging, and improves the uniformity of current distribution. The second lattice mica insulating layer has the following advantages: (1) Mica is a natural inorganic insulating material that is resistant to high temperatures (>600℃). When severe thermal runaway occurs inside the battery, the mica coating can still provide reliable physical insulation. After the thermal runaway of a single cell, the high temperature and flame will be rapidly transferred to the adjacent cells through the current collector (aluminum foil is also an excellent thermal conductor), triggering a chain thermal runaway. The mica layer has extremely low thermal conductivity and is an excellent thermal barrier. The dot-matrix mica coating can form "thermal insulation bridges" on the aluminum foil surface, significantly delaying the longitudinal conduction of heat along the aluminum foil, thus buying valuable time for the battery management system (BMS) to trigger protection measures. This design has strong high temperature resistance and insulation protection. (2) The dot-matrix design, rather than a full-coverage coating, leaves sufficient longitudinal transport channels for lithium ions, hardly increasing the resistance to ion migration, and ensuring that the ion transport channels are not blocked. (3) Cylindrical batteries will expand due to gas generation during cycling, generating stress. The dot-matrix structure is more flexible than a full-coverage coating and can better adapt to expansion without falling off.

[0095] Therefore, the positive current collector prepared by the high-safety composite positive current collector preparation method provided by the present invention can significantly improve the safety performance of batteries when applied in batteries, which is of great significance for the future development of batteries.

[0096] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-safety composite positive electrode current collector, characterized in that, The invention includes an aluminum foil substrate and a composite layer disposed on the upper and lower surfaces of the aluminum foil substrate. The composite layer includes a conductive carbon layer and a mica coating. The conductive carbon layer is disposed between the aluminum foil surface and the mica coating. The mica coating is composed of a lattice of dotted units arranged in an array. The aluminum foil has a thickness of 12-16 μm, the conductive carbon layer has a thickness of 0.5-3 μm, and the mica coating has a thickness of 0.5-3 μm; the lattice units in the mica coating include circular lattices with a diameter of 1-5 μm, and their distribution density is 40-60% of the area of ​​the conductive carbon layer. The mica coating contains mica particles, and the median particle size D50 of the mica particles is 1~8μm.

2. The high-safety composite positive electrode current collector according to claim 1, characterized in that, The conductive carbon layer contains a conductive agent, which includes any one or more of conductive carbon black, carbon nanotubes, graphene, and conductive graphite.

3. A method for preparing a high-safety composite positive electrode current collector according to any one of claims 1 or 2, characterized in that, Includes the following steps: S1, Aluminum foil substrate pretreatment: The aluminum foil to be coated is first cleaned with alkaline solution and deionized water in sequence, and then dried and surface treated to obtain the pretreated aluminum foil substrate. S2, Coating a conductive carbon layer: A conductive paste containing a conductive agent is coated on the upper and lower surfaces of the pretreated aluminum foil substrate described in S1, and after drying, a carbon-coated aluminum foil is obtained. S3, Pretreatment of carbon-coated aluminum foil: The carbon-coated aluminum foil described in S2 is subjected to surface treatment to obtain pretreated carbon-coated aluminum foil. S4, Coating with mica coating: Mica insulating slurry containing mica particles is coated on the upper and lower surfaces of the pretreated carbon-coated aluminum foil described in S3, and after drying, a high-safety composite positive current collector is obtained. The median particle size D50 of the mica insulating slurry is 0.5~1.0μm; The mica insulating slurry is uniformly coated onto the upper and lower surfaces of the pretreated carbon-coated aluminum foil described in S3 using a dot matrix coating method. After coating, a high-safety composite positive current collector is obtained after segmented heating and drying. The dot matrix coating includes gravure printing, and the segmented heating is divided into three stages: the first stage is 85±1℃, the second stage is 105±1℃, and the third stage is 110±1℃.

4. The method for preparing the high-safety composite positive current collector according to claim 3, characterized in that, The cleaning method using alkaline solution and deionized water described in S1 is as follows: spray with a sodium carbonate or sodium hydroxide solution with a mass concentration of 5~10wt% at 50~55℃ for 10~30s, and then rinse with deionized water until the conductivity is ≤10μS / cm.

5. The method for preparing the high-safety composite positive current collector according to claim 3, characterized in that, The surface treatment described in S1 includes corona treatment, with a frequency of 15±2 kHz and a voltage of 15±2 kV; the surface treatment described in S3 includes corona treatment, with a frequency of 5±1 kHz and a voltage of 5±1 kV.

6. The method for preparing the high-safety composite positive current collector according to claim 3, characterized in that, The conductive slurry in S2 comprises 1-10 wt% conductive agent, 0.5-4 wt% first binder, 90-98 wt% first solvent, and 0-1.5 wt% first dispersant; the first binder comprises acrylic acid, styrene-butadiene rubber, or polyvinylidene fluoride; the first solvent comprises deionized water, ethanol, or N-methylpyrrolidone; the first dispersant comprises polyvinylpyrrolidone, hydroxypropyltrimethylammonium chloride, chitosan, or polyethylene oxide; after mixing the conductive agent, first binder, first solvent, and first dispersant, the mixture is pre-dispersed for 0.5-1 hour, and then high-speed dispersed for 1-5 hours to obtain the conductive slurry, wherein the power of the high-speed dispersion is 3-5 times that of the pre-dispersion power.

7. The method for preparing the high-safety composite positive current collector according to claim 3, characterized in that, The mica insulating slurry described in S4 comprises 30-50 wt% mica particles, 50-68 wt% second solvent, 0.5-1.0 wt% second binder, and 0-1.5 wt% second dispersant; the second solvent comprises deionized water, the second binder comprises any one or more of styrene-butadiene rubber, polyacrylic acid, acrylic polymer, sodium carboxymethyl cellulose, and waterborne polyurethane, and the second dispersant comprises polyacrylate, phosphate salt, polyvinylpyrrolidone, or polyacrylic acid; the mica particles, second solvent, second binder, and second dispersant are ground to obtain a mica insulating slurry with a median particle size D50 of 0.5-1.0 μm.

8. An application of the high-safety composite positive current collector according to any one of claims 1 or 2, characterized in that, The high-safety composite positive electrode current collector is applied to a high-safety battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode includes the high-safety composite positive electrode current collector.

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