Positive electrode composite current collector, preparation method thereof and lithium ion battery

Abstract

The invention provides a positive electrode composite current collector, a preparation method thereof and a lithium ion battery. The positive electrode composite current collector comprises a base material layer, a first modified layer, a second modified layer, a first conductive layer and a second conductive layer. Wherein the material of the base material layer is selected from an organic polymer material; the first modified layer is arranged on the surface of one side of the base material layer; the second modified layer is arranged on the surface of the other side of the base material layer; the first conductive layer is arranged on the surface of one side, away from the substrate layer, of the first modified layer; the second conductive layer is arranged on the surface of one side, away from the substrate layer, of the second modified layer; the preparation method of the first modified layer and the second modified layer comprises the following steps: S1, mixing polyester resin, a cross-linking agent, an initiator and a solvent to obtain slurry; the solvent comprises styrene, and the cross-linking agent is an isocyanate compound; and S2, coating two side surfaces of the base material layer with the slurry, and carrying out a curing reaction to obtain the first modified layer and the second modified layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery preparation, in particular to a positive electrode composite current collector, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] The current collector is one of the important components of the lithium ion battery, which functions to carry active materials, collect and conduct electrons. The ideal lithium ion battery current collector should meet the following points: (1) high electrical conductivity; (2) good chemical and electrochemical stability; (3) high mechanical strength; (4) good compatibility and binding force with electrode active materials; (5) cheap and easy to obtain; (6) light weight.

[0003] The traditional current collector generally uses aluminum foil as the positive electrode current collector and copper foil as the negative electrode current collector. However, copper foil and aluminum foil are difficult to meet the increasingly high performance requirements of lithium ion battery current collectors. In order to improve the performance of the current collector, people have developed composite current collectors. Compared with traditional metal foils, composite current collectors have the advantages of high electrical conductivity, low cost and light weight.

[0004] However, the composite current collector currently still faces the following problems: (1) the adhesion between the metal layer and the polymer film of the composite current collector obtained by physical vapor deposition is poor, which easily causes the metal layer to peel off or fall off from the polymer film layer; (2) the surface of the polymer film is easily subjected to bombardment of metal particles in the magnetron and evaporation process, which may cause local rupture and degradation of the polymer macromolecules, resulting in a significant decrease in the mechanical properties of the polymer film, causing a risk of belt breakage and affecting the subsequent cell coating process.

[0005] In order to solve the above problems, the prior art adopts a double-layer coating, however, the preparation cost is high, the process is complicated, the adhesion between the layers is insufficient and the adhesion performance after electrolyte immersion is not studied, and the real test of the positive electrode composite current collector is the wet adhesion data after electrolyte immersion.

[0006] On this basis, it is of great significance to research and develop a positive electrode composite current collector with strong adhesion between the substrate and the metal layer, good mechanical properties, good safety, and low cost. SUMMARY

[0007] The main purpose of the present application is to provide a positive electrode composite current collector, a preparation method thereof and a lithium ion battery, to solve the problems of poor adhesion between the substrate and the metal layer, poor mechanical properties and high preparation cost of the positive electrode composite current collector in the prior art, especially the problem that the metal layer in the existing positive electrode composite current collector is easily peeled off or fallen off from the surface of the substrate after being immersed in electrolyte, causing the performance of the lithium ion battery to decrease.

[0008] In order to achieve the above-mentioned purpose, the present application provides a positive electrode composite current collector, which comprises: a substrate layer, a first modified layer, a second modified layer, a first conductive layer and a second conductive layer; the material of the substrate layer is selected from organic polymer materials; the first modified layer is arranged on one side surface of the substrate layer; the second modified layer is arranged on the other side surface of the substrate layer; the first conductive layer is arranged on the side surface of the first modified layer away from the substrate layer; the second conductive layer is arranged on the side surface of the second modified layer away from the substrate layer; the preparation method of the first modified layer and the second modified layer comprises: step S1, mixing polyester resin, crosslinking agent, initiator and solvent to obtain slurry; wherein the solvent comprises styrene, and the crosslinking agent is an isocyanate compound; step S2, coating the slurry on both side surfaces of the substrate layer to obtain the first modified layer and the second modified layer after curing reaction.

[0009] Further, the content of the polyester resin is 5-10wt% based on the weight percentage content of the slurry; preferably, the weight average molecular weight of the polyester resin is 10000-30000.

[0010] Further, the content of the crosslinking agent is 1-5wt% based on the weight percentage content of the slurry; preferably, the crosslinking agent is selected from one or more of the group consisting of hexamethylene diisocyanate, toluene diisocyanate and isophorone diisocyanate; preferably, the weight ratio of the polyester resin to the crosslinking agent is (5-10):(1-5).

[0011] Further, the content of the styrene is 5-10wt% based on the weight percentage content of the slurry.

[0012] Further, the content of the initiator is 1-5wt% based on the weight percentage content of the crosslinking agent; preferably, the initiator is selected from one or more of the group consisting of dibutyltin dilaurate, azobisisobutyronitrile and dibenzoyl peroxide.

[0013] Further, the crosslinking agent is hexamethylene diisocyanate, the initiator is dibutyltin dilaurate, and the weight ratio of the polyester resin, hexamethylene diisocyanate, styrene and dibutyltin dilaurate is (5-10):(1-5):(5-10):(0.1-0.25); preferably, the solvent further comprises one or more of the group consisting of methylcyclohexane, cyclohexane and toluene.

[0014] Further, the solid content of the slurry is 5-10wt%; preferably, the temperature of the curing reaction is 50-100℃, and the time is 1-10min; preferably, the coating process in step S2 is carried out by micro-gravure coating.

[0015] Further, the thickness of the first modification layer and the second modification layer is 0.2-1 μm; preferably, the thickness of the substrate layer is 2-12 μm; preferably, the thickness of the first conductive layer and the second conductive layer is 0.1-1.5 μm; preferably, the material of the substrate layer is selected from one or more of polyethylene, biaxially oriented polypropylene, polyethylene terephthalate, polyethylene naphthalate, poly-para-phenyleneterephthalamide, polyimide, polycarbonate, polyether ether ketone, polyoxymethylene, poly-p-phenylene sulfide, poly-p-phenylene oxide, polyvinyl chloride, polyamide, polytetrafluoroethylene; preferably, the material of the first conductive layer and the second conductive layer is metallic aluminum; preferably, the dry adhesion between the substrate layer and the first conductive layer or the second conductive layer is 3-10 N / 15 mm; the wet adhesion between the substrate layer and the first conductive layer or the second conductive layer is 3-7 N / 15 mm; preferably, the tensile strength of the positive electrode composite current collector in the MD direction is ≥240 MPa, and the tensile strength in the TD direction is ≥200 MPa.

[0016] To achieve the above object, another aspect of the present application further provides a preparation method of the positive electrode composite current collector according to any one of claims 1-8, the preparation method comprising: step S-A1, preparing a substrate layer; step S-A2, preparing a first modification layer and a second modification layer on the two side surfaces of the substrate layer, respectively; and step S-A3, depositing a first conductive layer on the side surface of the first modification layer away from the substrate layer, and depositing a second conductive layer on the side surface of the second modification layer away from the substrate layer, to obtain the positive electrode composite current collector.

[0017] Still another aspect of the present application provides a lithium ion battery, comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode comprises the above-mentioned positive electrode composite current collector and a positive electrode active material arranged on the surface of the positive electrode composite current collector.

[0018] The technical scheme of the present application is applied to the traditional positive electrode current collector, which comprises a first conductive layer, a substrate layer and a second conductive layer arranged in sequence. Compared with the positive electrode current collector with the structure, the positive electrode composite current collector provided by the present application further comprises a first modification layer arranged between the first conductive layer and the substrate layer, and a second modification layer arranged between the second conductive layer and the substrate layer, and the first modification layer and the second modification layer are prepared by the specific preparation method. The polyester resin as the main material of the modification layer can provide mechanical strength for the positive electrode composite current collector. In addition, the use of the polyester resin and the isocyanate compound can form a crosslinked network between the organic polymer material and the polyester resin, thereby significantly improving the tensile strength of the first modification layer and the second modification layer. The styrene can not only act as a solvent, but also can improve the rigidity and elastic modulus of the first modification layer and the second modification layer as a polymer monomer, thereby improving the tensile strength and other mechanical properties of the positive electrode composite current collector. The introduction of the initiator can improve the curing reaction efficiency, thereby shortening the preparation time of the modification layer.

[0019] Therefore, the positive electrode composite current collector provided by the present application has excellent tensile strength and other mechanical properties, good bonding force between the substrate layer and the conductive layer, and is not easy to peel off or fall off. After being soaked in electrolyte, it can still maintain good structural stability. When it is applied in the preparation process of lithium ion batteries, it can reduce the risk of belt breakage and inhibit the decline of the electrochemical performance and cycle stability of lithium ion batteries.

[0020] Another traditional positive electrode current collector comprises a first conductive layer, an aluminum oxide layer, a substrate layer, an aluminum oxide layer and a second conductive layer arranged in sequence, that is, the aluminum oxide layer is introduced between the first conductive layer and the second conductive layer and the substrate layer to improve the bonding force and adhesion between the first conductive layer and the second conductive layer and the substrate layer. However, the aluminum oxide layer is usually prepared by vacuum evaporation method, which results in high preparation cost. The first modification layer and the second modification layer provided by the present application can replace the above-mentioned aluminum oxide layer, and are prepared by coating method, which can significantly reduce the preparation cost of the positive electrode composite current collector. BRIEF DESCRIPTION OF DRAWINGS

[0021] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the description of the exemplary embodiments of the present application and the explanation thereof serve to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0022] Figure 1 A cross-sectional structure schematic diagram of the positive electrode composite current collector prepared in Example 1 of the present application is shown;

[0023] Figure 2 A cross-sectional structure schematic diagram of the positive electrode composite current collector prepared in Comparative Example 2 is shown.

[0024] The above figures include the following reference numerals:

[0025] 10. Substrate layer; 21. First modified layer; 22. Second modified layer; 31. First conductive layer; 32. Second conductive layer; 40. AlO x layer. Detailed Implementation

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0027] As described in the background section, existing positive electrode composite current collectors suffer from poor adhesion between the substrate and the metal layer, poor mechanical properties, and high manufacturing costs. In particular, the metal layer in existing positive electrode composite current collectors is prone to peeling or detaching from the substrate surface after immersion in electrolyte, leading to a decline in lithium-ion battery performance. To address these technical problems, the first aspect of this application provides a positive electrode composite current collector, such as... Figure 1 As shown, the positive electrode composite current collector includes: a substrate layer 10, a first modified layer 21, a second modified layer 22, a first conductive layer 31, and a second conductive layer 32. The substrate layer 10 is made of an organic polymer material; the first modified layer 21 is disposed on one side of the substrate layer 10; the second modified layer 22 is disposed on the other side of the substrate layer 10; the first conductive layer 31 is disposed on the side of the first modified layer 21 away from the substrate layer 10; the second conductive layer 32 is disposed on the side of the second modified layer 22 away from the substrate layer 10. The preparation method of the first modified layer 21 and the second modified layer 22 includes: step S1, mixing polyester resin, a crosslinking agent, an initiator, and a solvent to obtain a slurry; wherein the solvent includes styrene, and the crosslinking agent is an isocyanate compound; step S2, coating the slurry onto both sides of the substrate layer 10, and obtaining the first modified layer 21 and the second modified layer 22 after a curing reaction.

[0028] The traditional positive electrode current collector comprises a first conductive layer 31, a substrate layer 10 and a second conductive layer 32 which are sequentially stacked. Compared with the positive electrode current collector having the structure, the positive electrode composite current collector provided by the application further comprises a first modification layer 21 arranged between the first conductive layer 31 and the substrate layer 10, and a second modification layer 22 arranged between the second conductive layer 32 and the substrate layer 10, and the first modification layer 21 and the second modification layer 22 are prepared by the specific preparation method. The polyester resin as the main material of the modification layer can provide the positive electrode composite current collector with mechanical strength. Moreover, the use of the polyester resin and the isocyanate compound can form a crosslinked network between the organic polymer material and the polyester resin, thereby significantly improving the tensile strength of the first modification layer 21 and the second modification layer 22. The styrene can not only act as a solvent, but also act as a polymerization monomer to improve the rigidity and elastic modulus of the first modification layer 21 and the second modification layer 22, thereby improving the tensile strength and other mechanical properties of the positive electrode composite current collector. The introduction of the initiator can improve the curing reaction efficiency, thereby shortening the preparation time of the modification layer.

[0029] Therefore, the positive electrode composite current collector provided by the application has excellent tensile strength and other mechanical properties, good bonding force between the substrate layer 10 and the conductive layer, and is not easy to peel off or fall off. After being soaked in electrolyte, the positive electrode composite current collector can still maintain good structural stability, thereby reducing the risk of belt breakage and inhibiting the decline of the electrochemical performance and cycle stability of the lithium ion battery during the preparation of the lithium ion battery.

[0030] Another traditional positive electrode current collector comprises a first conductive layer 31, an aluminum oxide layer, a substrate layer 10, an aluminum oxide layer and a second conductive layer 32 which are sequentially stacked, that is, the aluminum oxide layer is introduced between the first conductive layer 31 and the second conductive layer 32 and the substrate layer 10 to improve the bonding force and adhesion between the first conductive layer 31 and the second conductive layer 32 and the substrate layer 10. However, the aluminum oxide layer is usually prepared by a vacuum evaporation method, resulting in high preparation cost. The first modification layer 21 and the second modification layer 22 provided by the application can replace the above-mentioned aluminum oxide layer, and are prepared by a coating method, thereby significantly reducing the preparation cost of the positive electrode composite current collector.

[0031] In a preferred embodiment, the content of the polyester resin is 5-10 wt% based on the weight percentage content of the slurry. The content of the polyester resin includes but is not limited to the above range, and the limitation of the content of the polyester resin in the above range is beneficial to improve the mechanical strength and tensile strength of the positive electrode composite current collector and reduce the risk of belt breakage.

[0032] In order to further improve the mechanical strength and tensile strength of the positive electrode composite current collector, preferably, the weight average molecular weight of the polyester resin is 10000-30000.

[0033] In a preferred embodiment, the crosslinking agent content is 1-5 wt% by weight of the slurry. The crosslinking agent content includes, but is not limited to, the above range. Limiting it within the above range is beneficial to improving the mechanical strength and tensile strength of the positive electrode composite current collector and reducing the risk of strip breakage.

[0034] To further improve the mechanical strength and tensile strength of the positive electrode composite current collector, preferably, the crosslinking agent includes, but is not limited to, one or more of the group consisting of hexamethylene diisocyanate, toluene diisocyanate and isophorone diisocyanate.

[0035] In a preferred embodiment, the weight ratio of polyester resin to crosslinking agent is (5-10):(1-5). The weight ratio of polyester resin to crosslinking agent includes, but is not limited to, the above range. Limiting it to the above range is beneficial to further improve the tensile strength of the first modified layer 21 and the second modified layer 22, thereby further improving the tensile strength of the positive electrode composite current collector and further reducing the risk of strip breakage.

[0036] In a preferred embodiment, the styrene content is 5-10 wt% by weight of the slurry. The styrene content includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improving the rigidity and elastic modulus of the first modified layer 21 and the second modified layer 22, thereby improving the mechanical properties of the positive electrode composite current collector and reducing the risk of strip breakage.

[0037] In a preferred embodiment, the initiator content is 1-5 wt% based on the weight percentage of the crosslinking agent. The initiator content includes, but is not limited to, the above range. Limiting it within the above range is beneficial to improving the curing reaction efficiency, thereby shortening the preparation time of the first modified layer 21 and the second modified layer 22.

[0038] To further improve the efficiency of the curing reaction, preferably, the initiator includes, but is not limited to, one or more of the group consisting of dibutyltin dilaurate, azobisisobutyronitrile, and benzoyl peroxide.

[0039] In a preferred embodiment, the crosslinking agent is hexamethylene diisocyanate, the initiator is dibutyltin dilaurate, and the weight ratio of polyester resin, hexamethylene diisocyanate, styrene, and dibutyltin dilaurate is (5-10):(1-5):(5-10):(0.1-0.25). Compared to other ranges, using the above-mentioned preferred ratio of components for compounding is beneficial to better exert the synergistic effect of each component in the slurry, to further improve the mechanical properties of the positive electrode composite current collector, to further improve the adhesion between the substrate layer 10 and the first conductive layer 31 or the second conductive layer 32, thereby further improving the structural stability of the positive electrode composite current collector after being immersed in the electrolyte, suppressing the peeling and detachment of the first conductive layer 31 or the second conductive layer 32, and its application in lithium-ion batteries is beneficial to further reduce the risk of band breakage, and further suppress the decline in the electrochemical performance and cycle stability of lithium-ion batteries.

[0040] This application does not specifically limit the type of solvent used in the slurry preparation process; any solvent that can improve the compatibility of the components in the slurry can be used. In a preferred embodiment, the solvent includes, but is not limited to, one or more of the group consisting of styrene, methylcyclohexane, cyclohexane, and toluene.

[0041] In a preferred embodiment, the solid content of the slurry is 5 to 10 wt%. The solid content of the slurry includes, but is not limited to, the above range. Limiting it to the above range facilitates the coating of the slurry, improves its processability, and facilitates the control of the coating thickness.

[0042] In order to improve the curing reaction efficiency and thus better leverage the advantages of the first modified layer 21 and the second modified layer 22, thereby improving the adhesion between the substrate layer 10 and the first conductive layer 31 and the second conductive layer 32, preferably, the curing reaction temperature is 50-100°C and the time is 1-10 min.

[0043] Microgravure coating is a contact coating method. In a preferred embodiment, the coating process in step S2 is performed using microgravure coating. This coating method facilitates improved processing efficiency and allows for easy control of the thickness of the first modified layer 21 and the second modified layer 22.

[0044] In a preferred embodiment, the thickness of the first modified layer 21 and the second modified layer 22 is 0.2–1 μm. Compared to other ranges, limiting the thickness of the first modified layer 21 and the second modified layer 22 to the above range is beneficial to improving the energy density of the lithium-ion battery while reducing the thickness of the positive electrode composite current collector, and at the same time, it is beneficial to reduce the risk of the first conductive layer 31 and the second conductive layer 32 falling off or peeling off, thereby extending the service life of the lithium-ion battery.

[0045] To reduce the weight of the positive electrode composite current collector and to improve its flexibility, the thickness of the substrate layer 10 is preferably 2 to 12 μm.

[0046] In a preferred embodiment, the thickness of the first conductive layer 31 and the second conductive layer 32 is 0.1 to 1.5 μm. Compared to other ranges, limiting the thickness of the first conductive layer 31 and the second conductive layer 32 to the above range is beneficial to improving the conductivity of the positive electrode composite current collector.

[0047] This application does not specifically limit the material of the substrate layer 10, as long as it can support the conductive layer. In a preferred embodiment, the material of the substrate layer 10 includes, but is not limited to, one or more of the following: polyethylene, biaxially oriented polypropylene, polyethylene terephthalate, polyethylene naphthalate, poly(p-phenylene terephthalate), polyimide, polycarbonate, polyetheretherketone, polyoxymethylene, polyphenylene sulfide, poly(p-phenylene ether), polyvinyl chloride, polyamide, and polytetrafluoroethylene.

[0048] In order to adapt to the positive electrode composite current collector, and in order to improve conductivity and reduce cost, preferably, the first conductive layer 31 and the second conductive layer 32 are made of aluminum.

[0049] The positive electrode composite current collector provided in this application has excellent dry and wet bonding strength, and the conductive layer is not easily peeled off or detached after being immersed in electrolyte. In a preferred embodiment, the dry bonding strength between the substrate layer 10 and the first conductive layer 31 or the second conductive layer 32 is 3 to 10 N / 15 mm; the wet bonding strength between the substrate layer 10 and the first conductive layer 31 or the second conductive layer 32 is 3 to 7 N / 15 mm.

[0050] The positive electrode composite current collector provided in this application exhibits excellent tensile strength in both the MD direction (longitudinal direction) and the TD direction (transverse direction). In a preferred embodiment, the tensile strength of the positive electrode composite current collector in the MD direction is ≥240MPa, and the tensile strength in the TD direction is ≥200MPa.

[0051] The second aspect of this application also provides a method for preparing the above-mentioned positive electrode composite current collector provided in this application. The method for preparing the positive electrode composite current collector includes: step S-A1, preparing a substrate layer 10 for later use; step S-A2, preparing a first modified layer 21 and a second modified layer 22 on both sides of the substrate layer 10 respectively; step S-A3, depositing a first conductive layer 31 on the side of the first modified layer 21 away from the substrate layer 10, and depositing a second conductive layer 32 on the side of the second modified layer 22 away from the substrate layer 10, thereby obtaining the positive electrode composite current collector.

[0052] Using the above method, a first modified layer 21 and a second modified layer 22 are prepared on both sides of the substrate layer 10, and then a first conductive layer 31 and a second conductive layer 32 are deposited respectively. The preparation method provided in this application is simple to operate, and the resulting positive electrode composite current collector has excellent mechanical properties such as tensile strength. Furthermore, the bonding force between the substrate layer 10 and the conductive layer is good, making it difficult to peel or detach. Even after being immersed in electrolyte, it can still maintain good structural stability. Applying it to the lithium-ion battery manufacturing process can reduce the risk of band breakage and suppress the decline in the electrochemical performance and cycle stability of the lithium-ion battery.

[0053] Compared to the traditional magnetron sputtering method for preparing alumina layers, the preparation method of the first modified layer 21 and the second modified layer 22 provided in this application includes the above-mentioned slurry coating process, which can significantly reduce the preparation cost of the positive electrode composite current collector.

[0054] In a preferred embodiment, the first conductive layer 31 and the second conductive layer 32 are deposited using a vapor deposition method. Depositing the first conductive layer 31 and the second conductive layer 32 using the above method facilitates control over the thickness and density of the deposited layers, which is beneficial for improving the conductivity of the negative electrode composite current collector. The vapor deposition method can be either barrier vapor deposition or electron gun vapor deposition.

[0055] In a preferred embodiment, step S-A1 further includes corona treatment of the substrate layer 10. Corona treatment of the substrate layer 10 helps to improve the surface roughness and reactivity of the substrate layer 10, thereby facilitating the subsequent preparation of the first modified layer 21 and the second modified layer 22.

[0056] A third aspect of this application also provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. The positive electrode includes the aforementioned positive electrode composite current collector provided in this application and a positive electrode active material disposed on the surface of the positive electrode composite current collector. The aforementioned positive electrode composite current collector provided in this application has excellent mechanical properties such as tensile strength, and the bonding force between the substrate layer 10 and the conductive layer is good, making it difficult to peel off or detach. Even after being immersed in the electrolyte, it can still maintain good structural stability. Its application in the lithium-ion battery manufacturing process can reduce the risk of band breakage and suppress the decline in the electrochemical performance and cycle stability of the lithium-ion battery. In addition, compared with the traditional magnetron sputtering method for preparing the alumina layer, the preparation method of the first modified layer 21 and the second modified layer 22 provided in this application includes the aforementioned slurry coating process, which can significantly reduce the preparation cost of the positive electrode composite current collector, thereby reducing the manufacturing cost of the lithium-ion battery.

[0057] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0058] Example 1

[0059] A method for preparing a positive electrode composite current collector, comprising:

[0060] (1) A PET film with a thickness of 6 μm was subjected to corona treatment at 3000W, and the treated PET film was put into use.

[0061] (2) Dissolve 5g of hexamethylene diisocyanate and 5g of polyester resin with a weight average molecular weight of 20,000 in a mixed solvent of 10g of styrene and 80g of methylcyclohexane, then add 0.1g of dibutyltin dilaurate, stir at 80°C for 2 hours, and simultaneously perform ultrasonic treatment to obtain a slurry; wherein, the solid content of the slurry is 10wt%; the weight ratio of styrene to methylcyclohexane in the mixed solvent is 1:8;

[0062] (3) The above slurry obtained in step (2) is coated on the upper and lower surfaces of the corona-treated PET film using a micro-gravure coating machine (Kejing, MSK-AFA-MG200). After curing at 80°C for 10 minutes, a first laminated structure is obtained. The first laminated structure includes a first modified layer 21, a substrate layer 10 and a second modified layer 22 stacked in sequence.

[0063] (4) Using an electron gun evaporation method, aluminum is evaporated on the surface of the first modified layer 21 away from the substrate layer 10 to form the first conductive layer 31, and aluminum is evaporated on the surface of the second modified layer 22 away from the substrate layer 10 to form the second conductive layer 32, thus obtaining the positive electrode composite current collector; wherein, during the evaporation process, the temperature of the main roller is 5℃, the film forming speed is 10m / min, and the bias voltage is 450V.

[0064] The positive electrode composite current collector prepared in Example 1 has Figure 1 The structure shown has a first modified layer 21 and a second modified layer 22 with a thickness of 300 nm, and a first conductive layer 31 and a second conductive layer 32 with a thickness of 1 μm.

[0065] Example 2

[0066] The difference from Example 1 is that the amount of polyester resin used is changed so that it accounts for 5 wt% of the slurry.

[0067] In the prepared positive electrode composite current collector, the thicknesses of the first modified layer 21 and the second modified layer 22 are the same as those in Example 1.

[0068] Example 3

[0069] The difference from Example 1 is that the amount of polyester resin used is changed so that it accounts for 10 wt% of the slurry.

[0070] In the prepared positive electrode composite current collector, the thicknesses of the first modified layer 21 and the second modified layer 22 are the same as those in Example 1.

[0071] Example 4

[0072] The difference from Example 1 is that the amount of polyester resin used is changed so that it accounts for 15 wt% of the slurry.

[0073] In the prepared positive electrode composite current collector, the thicknesses of the first modified layer 21 and the second modified layer 22 are the same as those in Example 1.

[0074] Example 5

[0075] The difference from Example 1 is that the amount of hexamethylene diisocyanate was changed so that it accounted for 1 wt% of the slurry.

[0076] In the prepared positive electrode composite current collector, the thicknesses of the first modified layer 21 and the second modified layer 22 are the same as those in Example 1.

[0077] Example 6

[0078] The difference from Example 1 is that the amount of hexamethylene diisocyanate was changed to 6 wt% of the slurry.

[0079] In the prepared positive electrode composite current collector, the thicknesses of the first modified layer 21 and the second modified layer 22 are the same as those in Example 1.

[0080] Example 7

[0081] The difference from Example 1 is that the amount of dibutyltin dilaurate is changed so that its weight percentage of hexamethylene diisocyanate is 1 wt%.

[0082] In the prepared positive electrode composite current collector, the thicknesses of the first modified layer 21 and the second modified layer 22 are the same as those in Example 1.

[0083] Example 8

[0084] The difference from Example 1 is that the amount of dibutyltin dilaurate is changed so that its weight percentage of hexamethylene diisocyanate is 5 wt%.

[0085] In the prepared positive electrode composite current collector, the thicknesses of the first modified layer 21 and the second modified layer 22 are the same as those in Example 1.

[0086] Example 9

[0087] The difference from Example 1 is that the amount of dibutyltin dilaurate is changed so that its weight percentage of hexamethylene diisocyanate is 6 wt%.

[0088] In the prepared positive electrode composite current collector, the thicknesses of the first modified layer 21 and the second modified layer 22 are the same as those in Example 1.

[0089] Example 10

[0090] The difference from Example 1 is that in step (3), the curing reaction temperature is 50°C.

[0091] Example 11

[0092] The difference from Example 1 is that in step (3), the curing reaction temperature is 100°C and the time is 1 min.

[0093] Comparative Example 1

[0094] The difference from Example 1 is that steps (2) and (3) are omitted, and aluminum is vapor-deposited on both sides of the corona-treated PET film.

[0095] Comparative Example 2

[0096] The difference from Example 1 is that steps (2) and (3) are replaced by the following steps, including: preparing a layer of AlO with a light transmittance of 85% on each of the two surfaces of the corona-treated PET film. x Layer 40 is used to obtain the second stacked structure.

[0097] The positive electrode composite current collector prepared in Comparative Example 2 has Figure 2 The structure shown includes a first conductive layer 31 and AlO2 layers stacked sequentially. x Layer 40, Substrate Layer 10, AlO x Layer 40 and second conductive layer 32; wherein, AlO x The thickness of layer 40 is 10 nm.

[0098] The sheet resistance of the positive electrode composite current collectors prepared in all the above embodiments and comparative examples of this application was tested using the four-probe method. The tensile strength of the positive electrode composite current collectors in the MD and TD directions was tested according to GB / T 1040.1-2018 "Determination of Tensile Properties of Plastics". The peel strength of the first conductive layer 31 and the second conductive layer 32 was tested using the current collector peel strength testing method provided in Chinese Patent Application 202310804230.2, under both dry conditions and electrolyte immersion conditions (85℃, immersion for 3 days). The electrolyte used was a commercial electrolyte, model Hairong 9212. The test results are shown in Table 1.

[0099] In all the embodiments and comparative examples of this application, a positive electrode active material layer was coated onto the surface of the positive electrode composite current collector, wherein the positive electrode active material was NCM811, graphite was used as the negative electrode, a ceramic membrane was used as the separator, and 1 mol / L LiPF6 electrolyte (solvents included DMC and DC) was used to assemble a lithium-ion battery. Its energy density and cycle stability were tested. The coulombic efficiency method was used to test lithium plating. The cycle stability test conditions were: voltage range of 2.85V to 4.25V, 1C constant current charge-discharge. The test results are shown in Table 2.

[0100] Table 1

[0101]

[0102] Table 2

[0103] Internal resistance (mΩ) Number of turns required for discharge at room temperature to 80% capacity retention Example 1 9.54 1785 Example 2 10.50 1654 Example 3 11.32 1542 Example 4 11.95 1321 Example 5 12.31 1300 Example 6 13.10 1219 Example 7 14.21 1189 Example 8 15.01 1087 Example 9 15.98 1011 Example 10 16.77 989 Example 11 18.41 854 Comparative Example 1 32.11 321 Comparative Example 2 35.10 279

[0104] From the above description, it can be seen that the embodiments of the present invention achieve the following technical effects: A conventional positive electrode current collector includes a first conductive layer 31, a substrate layer 10, and a second conductive layer 32 stacked sequentially. Compared to a positive electrode current collector with this structure, the positive electrode composite current collector provided in this application further includes a first modified layer 21 between the first conductive layer 31 and the substrate layer 10, and a second modified layer 22 between the second conductive layer 32 and the substrate layer 10. The first modified layer 21 and the second modified layer 22 are prepared using the specific preparation method described above. Polyester resin, as the main material of the modified layer, can form a cross-linked network between the organic polymer material and the polyester resin, thereby providing mechanical strength to the positive electrode composite current collector. Furthermore, the combination of polyester resin and isocyanate compounds can significantly improve the tensile strength of the first modified layer 21 and the second modified layer 22. Styrene not only acts as a solvent but also as a polymer monomer to improve the rigidity and elastic modulus of the first modified layer 21 and the second modified layer 22, thereby improving the tensile strength and other mechanical properties of the positive electrode composite current collector. The introduction of an initiator can improve the efficiency of the curing reaction, thereby shortening the preparation time of the modified layer.

[0105] Therefore, the positive electrode composite current collector provided in this application has excellent mechanical properties such as tensile strength, and the bonding force between the substrate layer 10 and the conductive layer is good, making it difficult to peel off or fall off. It can still maintain good structural stability after being soaked in electrolyte. Applying it in the lithium-ion battery manufacturing process can reduce the risk of band breakage and suppress the decline in the electrochemical performance and cycle stability of lithium-ion batteries.

[0106] Another conventional positive electrode current collector includes a first conductive layer 31, an alumina layer, a substrate layer 10, an alumina layer, and a second conductive layer 32 stacked sequentially. Specifically, an alumina layer is introduced between the first and second conductive layers 31 and the substrate layer 10 to improve the bonding and adhesion between them. However, the alumina layer is typically prepared using vacuum evaporation, resulting in high manufacturing costs. The first modified layer 21 and the second modified layer 22 provided in this application can replace the aforementioned alumina layer and are prepared using a coating method, significantly reducing the manufacturing cost of the positive electrode composite current collector.

[0107] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0108] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A positive electrode composite current collector, characterized by, The positive electrode composite current collector comprises: a substrate layer (10) whose material is selected from organic polymer materials; a first modified layer (21) arranged on one side surface of the substrate layer (10); a second modified layer (22) arranged on the other side surface of the substrate layer (10); a first conductive layer (31) arranged on the side surface of the first modified layer (21) away from the substrate layer (10); a second conductive layer (32) arranged on the side surface of the second modified layer (22) away from the substrate layer (10); The preparation method of the first modified layer (21) and the second modified layer (22) comprises: Step S1, mixing polyester resin, crosslinking agent, initiator and solvent to obtain slurry; wherein the solvent comprises styrene, and the crosslinking agent is an isocyanate compound; Step S2, coating the slurry on the two side surfaces of the substrate layer (10), and obtaining the first modified layer (21) and the second modified layer (22) after curing reaction.

2. The positive composite current collector of claim 1, wherein The content of the polyester resin is 5-10wt% based on the weight percentage of the slurry; Preferably, the weight average molecular weight of the polyester resin is 10000-30000.

3. The positive composite current collector of claim 1, wherein The content of the crosslinking agent is 1-5wt% based on the weight percentage of the slurry; Preferably, the crosslinking agent is selected from one or more of the group consisting of hexamethylene diisocyanate, toluene diisocyanate and isophorone diisocyanate; Preferably, the weight ratio of the polyester resin to the crosslinking agent is (5-10):(1-5).

4. The positive composite current collector according to any one of claims 1 to 3, characterized in that, The content of the styrene is 5-10wt% based on the weight percentage of the slurry.

5. The positive composite current collector of claim 4, wherein The content of the initiator is 1-5wt% based on the weight percentage of the crosslinking agent; Preferably, the initiator is selected from one or more of the group consisting of dibutyltin dilaurate, azobisisobutyronitrile and dibenzoyl peroxide.

6. The positive composite current collector of claim 1, wherein The crosslinking agent is hexamethylene diisocyanate, the initiator is dibutyltin dilaurate, and the weight ratio of the polyester resin, the hexamethylene diisocyanate, the styrene, the dibutyltin dilaurate is (5-10):(1-5):(5-10):(0.1-0.25); Preferably, the solvent further comprises one or more of the group consisting of methylcyclohexane, cyclohexane and toluene.

7. The positive composite current collector of claim 1, wherein The solid content of the slurry is 5-10wt%; Preferably, the temperature of the curing reaction is 50-100℃, and the time is 1-10min; Preferably, the coating process in the step S2 is carried out by micro-gravure coating.

8. The positive composite current collector according to any one of claims 1 to 7, wherein, The thickness of the first modified layer (21) and the second modified layer (22) is 0.2-1μm; Preferably, the thickness of the substrate layer (10) is 2-12μm; Preferably, the thickness of the first conductive layer (31) and the second conductive layer (32) is 0.1-1.5μm; Preferably, the material of the substrate layer (10) is selected from one or more of polyethylene, biaxially oriented polypropylene, polyethylene terephthalate, polyethylene naphthalate, poly (p-phenylene terephthalamide), polyimide, polycarbonate, polyether ether ketone, polyoxymethylene, poly (p-phenylene sulfide), poly (p-phenylene oxide), polyvinyl chloride, polyamide, polytetrafluoroethylene; Preferably, the material of the first conductive layer (31) and the second conductive layer (32) is aluminum; Preferably, the dry bonding force between the substrate layer (10) and the first conductive layer (31) or the second conductive layer (32) is 3-10 N / 15 mm; the wet bonding force between the substrate layer (10) and the first conductive layer (31) or the second conductive layer (32) is 3-7 N / 15 mm; Preferably, the tensile strength of the positive electrode composite current collector in the MD direction is ≥240 MPa, and the tensile strength in the TD direction is ≥200 MPa.

9. A method of producing the positive electrode composite current collector according to any one of claims 1 to 8, characterized by, The preparation method of the positive electrode composite current collector comprises: Step S-A1, preparing a substrate layer (10); Step S-A2, preparing a first modified layer (21) and a second modified layer (22) on the two side surfaces of the substrate layer (10), respectively; Step S-A3, depositing a first conductive layer (31) on the side surface of the first modified layer (21) away from the substrate layer (10), and depositing a second conductive layer (32) on the side surface of the second modified layer (22) away from the substrate layer (10), to obtain the positive electrode composite current collector.

10. A lithium ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, characterized by, The positive electrode comprises the positive electrode composite current collector according to any one of claims 1-8 and a positive electrode active material arranged on the surface of the positive electrode composite current collector.

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