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

Abstract

The invention provides a negative electrode composite current collector, a preparation method thereof and a lithium ion battery. The negative 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 base material layer is made of biaxially oriented polypropylene; 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 an isocyanate compound, acrylic acid, a modifier, a photoinitiator, a catalyst and a solvent to obtain slurry; wherein the isocyanate compound comprises an aromatic group, and the modifier contains an amino group; and S2, coating two side surfaces of a base material layer with the slurry, and carrying out a curing reaction under an ultraviolet irradiation condition to obtain a first modified layer and a second modified layer.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery manufacturing technology, and more specifically, to a negative electrode composite current collector, its preparation method, and a lithium-ion battery. Background Technology

[0002] Current collectors are an important component of lithium-ion batteries, and their function is to carry active materials and collect and conduct electrons. An ideal lithium-ion battery current collector should meet the following requirements: (1) high conductivity; (2) good chemical and electrochemical stability; (3) high mechanical strength; (4) good compatibility and binding force with electrode active materials; (5) low cost and easy availability; and (6) light weight.

[0003] Traditional current collectors typically use aluminum foil as the positive electrode and copper foil as the negative electrode. However, copper and aluminum foils are insufficient to meet the increasingly demanding performance requirements of lithium-ion battery current collectors. To improve current collector performance, composite current collectors have been developed. Compared to traditional metal foils, composite current collectors offer advantages such as high conductivity, low cost, and light weight.

[0004] However, composite current collectors still face 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 can easily cause the metal layer to peel off or fall off from the polymer film; (2) The surface of the polymer film is easily bombarded by metal particles in the magnetron and vapor deposition process, which may cause local breakage and degradation of polymer macromolecules, resulting in a significant decrease in the mechanical properties of the polymer film, triggering the risk of strip breakage, and affecting the subsequent cell coating process.

[0005] To address the aforementioned issues, existing technologies employ a double-layer coating. However, this method is costly and cumbersome to prepare, and the adhesion between the layers is insufficient. Furthermore, the adhesion performance after electrolyte immersion has not been studied. The real test for negative electrode composite current collectors lies in the wet bonding strength data after electrolyte immersion.

[0006] Based on this, it is of great significance to study and develop a negative electrode composite current collector with strong interlayer bonding and good mechanical properties. Summary of the Invention

[0007] The main objective of this invention is to provide a negative electrode composite current collector, its preparation method, and a lithium-ion battery, in order to solve the problem that existing negative electrode composite current collectors are difficult to have excellent mechanical properties while also having excellent interlayer bonding and heat resistance. In particular, the metal layer of existing negative electrode composite current collectors is easily peeled off or detached from the polymer layer surface after being immersed in electrolyte, causing a decrease in the performance of lithium-ion batteries.

[0008] To achieve the above objectives, the present invention provides a negative electrode composite current collector, comprising: a substrate layer, a first modified layer, a second modified layer, a first conductive layer, and a second conductive layer. The substrate layer is made of biaxially oriented polypropylene; the first modified layer is disposed on one side surface of the substrate layer; the second modified layer is disposed on the other side surface of the substrate layer; the first conductive layer is disposed on the side surface of the first modified layer away from the substrate layer; the second conductive layer is disposed on the side surface of the second modified layer away from the substrate layer; the preparation method of the first and second modified layers comprises: step S1, mixing an isocyanate compound, acrylic acid, a modifier, a photoinitiator, a catalyst, and a solvent to obtain a slurry; wherein the isocyanate compound includes aromatic groups, and the modifier contains amino groups; step S2, coating the slurry onto both sides of the substrate layer, and performing a curing reaction under ultraviolet light irradiation to obtain the first and second modified layers.

[0009] Further, the content of isocyanate compounds is 1 to 5 wt% based on the weight percentage of the slurry; preferably, the isocyanate compounds are selected from diphenylmethane diisocyanate and / or toluene diisocyanate.

[0010] Further, the acrylic acid content is 1-5 wt% by weight of the slurry; preferably, the modifier is thiourea; more preferably, the modifier is thiourea, and the thiourea content is 1-3 wt% by weight of the slurry.

[0011] Further, the photoinitiator content is 1-3 wt% based on the weight percentage of acrylic acid; preferably, the photoinitiator is selected from one or more of the group consisting of 2-hydroxy-2-methyl-1-phenyl-1-propanone, ethyl 2,4,6-trimethylbenzoylphenylphosphonate and 2-hydroxy-2-methyl-1-phenylpropanone; preferably, the catalyst content is 0.5-3 wt% based on the weight percentage of isocyanate compounds; preferably, the catalyst is selected from organotin compounds, more preferably stannous octoate and / or dibutyltin dilaurate.

[0012] Further, the solid content of the slurry is 5-10 wt%; preferably, the solvent is selected from one or more of the group consisting of toluene, ethyl acetate and acetone; preferably, during the curing reaction, an ultraviolet light source is used to provide ultraviolet light irradiation conditions, the power of the ultraviolet light source is 1000-1500W, and the curing reaction time is 15-60s.

[0013] Further, the thickness of the first modified layer and the second modified layer are each independently selected from 0.2 to 1 μm; preferably, the thickness of the substrate layer is 2 to 12 μm, more preferably 2 to 6.5 μm, and even more preferably 2.4 to 4.5 μm; preferably, the thickness of the first conductive layer and the second conductive layer are each independently selected from 0.1 to 1.51 μm; preferably, the first conductive layer and the second conductive layer are each independently selected from copper layers.

[0014] Furthermore, a first metal oxide layer is disposed between the first modified layer and the first conductive layer, and a second metal oxide layer is disposed between the second modified layer and the second conductive layer; preferably, the thicknesses of the first metal oxide layer and the second metal oxide layer are independently selected from 0.01 to 0.1 μm; preferably, the first metal oxide layer and the second metal oxide layer are independently selected from copper oxide layers.

[0015] Furthermore, the dry bonding force between the substrate layer and the first conductive layer or the second conductive layer is 3 to 10 N / 15 mm; the wet bonding force between the substrate layer and the first conductive layer or the second conductive layer is 3 to 7 N / 15 mm; preferably, the tensile strength of the negative electrode composite current collector in the MD direction is ≥200 MPa, and the tensile strength in the TD direction is ≥170 MPa.

[0016] To achieve the above objectives, another aspect of the present invention provides a method for preparing the negative electrode composite current collector provided in this application. The method for preparing the negative electrode composite current collector includes: step S-A1, preparing a substrate layer for later use; step S-A2, preparing a first modified layer and a second modified layer on both sides of the substrate layer respectively; step S-A3, depositing a first conductive layer on the side of the first modified layer away from the substrate layer, and depositing a second conductive layer on the side of the second modified layer away from the substrate layer, thereby obtaining the negative electrode composite current collector.

[0017] Another aspect of the present invention provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. The negative electrode includes the negative electrode composite current collector provided in this application and a negative electrode active material disposed on the surface of the negative electrode composite current collector.

[0018] Traditional negative electrode composite current collectors include a first conductive layer, a substrate layer, and a second conductive layer stacked sequentially. Applying the technical solution of this invention, the negative electrode composite current collector provided in this application further includes a first modified layer disposed between the first conductive layer and the substrate layer, and a second modified layer disposed between the second conductive layer and the substrate layer. The first and second modified layers provided in this application are prepared using the specific method described above. The isocyanate compounds include aromatic groups, and the introduction of aromatic groups can improve the rigidity and tensile strength of the subsequently prepared first and second modified layers. During the curing reaction, the isocyanate compounds can bond with the modifier to form a cross-linked network structure. Simultaneously, the amino groups in the modifier can form strong bonds with the metal elements in the first and second conductive layers, thereby improving the bonding force between the first modified layer and the first conductive layer, and between the second modified layer and the second conductive layer.

[0019] Compared to PET, BOPP has better inertness and resistance to electrolyte corrosion, but poorer heat resistance. Introducing the aforementioned first and second modified layers into the structure of a traditional negative electrode composite current collector can further improve its heat resistance. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0021] Figure 1 A schematic diagram of the cross-sectional structure of the negative electrode composite current collector in a preferred embodiment of this application is shown;

[0022] Figure 2 A schematic diagram of the cross-sectional structure of the negative electrode composite current collector in another preferred embodiment of this application is shown.

[0023] The above figures include the following reference numerals:

[0024] 10. Substrate layer; 21. First modified layer; 22. Second modified layer; 31. First conductive layer; 32. Second conductive layer; 41. First metal oxide layer; 42. Second metal oxide layer. Detailed Implementation

[0025] 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.

[0026] As described in the background section, existing negative electrode composite current collectors suffer from the problem of not being able to simultaneously possess excellent mechanical properties, excellent interlayer bonding, and heat resistance. In particular, after immersion in electrolyte, the metal layer in existing negative electrode composite current collectors is prone to peeling or detaching from the polymer layer surface, causing a decline in lithium-ion battery performance. To solve the above technical problems, this application provides a negative electrode composite current collector, such as... Figure 1 As shown, the negative 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 biaxially oriented polypropylene (BOPP). 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 an isocyanate compound, acrylic acid, a modifier, a photoinitiator, a catalyst, and a solvent to obtain a slurry; wherein the isocyanate compound includes aromatic groups, and the modifier contains amino groups; step S2, coating the slurry onto both sides of the substrate layer 10 and curing it under ultraviolet light irradiation to obtain the first modified layer 21 and the second modified layer 22.

[0027] Traditional negative electrode composite current collectors include a first conductive layer 31, a substrate layer 10, and a second conductive layer 32 stacked sequentially. The negative electrode composite current collector provided in this application further includes a first modified layer 21 disposed between the first conductive layer 31 and the substrate layer 10, and a second modified layer 22 disposed between the second conductive layer 32 and the substrate layer 10. The first modified layer 21 and the second modified layer 22 provided in this application are prepared using the specific method described above. The isocyanate compound includes aromatic groups, and the introduction of aromatic groups can improve the rigidity and tensile strength of the subsequently prepared first modified layer 21 and second modified layer 22. During the curing reaction, the isocyanate compound can bond with the modifier to form a cross-linked network structure. Simultaneously, the amino groups in the modifier can form strong bonds with the metal elements in the first conductive layer 31 and the second conductive layer 32, thereby improving the bonding force between the first modified layer 21 and the first conductive layer 31, and between the second modified layer 22 and the second conductive layer 32.

[0028] Compared to PET, BOPP has better inertness and resistance to electrolyte corrosion, but poorer heat resistance. Introducing the aforementioned first modified layer 21 and second modified layer 22 into the structure of a traditional negative electrode composite current collector can further improve its heat resistance.

[0029] In a preferred embodiment, the content of isocyanate compounds is 1-5 wt% by weight of the slurry. The content of isocyanate compounds includes, but is not limited to, the above range, and limiting it within the above range is beneficial to improving the rigidity and tensile strength of the negative electrode composite current collector.

[0030] To further improve the rigidity and tensile strength of the negative electrode composite current collector, preferably, the isocyanate compounds include, but are not limited to, diphenylmethane diisocyanate and / or toluene diisocyanate.

[0031] In a preferred embodiment, the acrylic acid content is 1 to 5 wt% by weight of the slurry. The acrylic acid content includes, but is not limited to, the above range, and limiting it within the above range is beneficial to improving the bonding force between the first modified layer 21 and the first conductive layer 31, as well as the bonding force between the second modified layer 22 and the second conductive layer 32.

[0032] To further improve the bonding force between the first modified layer 21 and the first conductive layer 31, and between the second modified layer 22 and the second conductive layer 32, preferably, the modifier is thiourea.

[0033] To further improve the bonding force between the first modified layer 21 and the first conductive layer 31, and between the second modified layer 22 and the second conductive layer 32, more preferably, the modifier is thiourea, and the content of thiourea is 1 to 3 wt% based on the weight percentage of the slurry.

[0034] In a preferred embodiment, the photoinitiator content is 1-3 wt% based on the weight percentage of acrylic acid. The photoinitiator content includes, but is not limited to, the above range. Limiting it within the above range is beneficial to improving the curing reaction effect, thereby improving the overall performance of the negative electrode composite current collector, such as tensile strength.

[0035] To further improve the overall performance of the negative electrode composite current collector, such as tensile strength, preferably, the photoinitiator includes, but is not limited to, one or more of the group consisting of 2-hydroxy-2-methyl-1-phenyl-1-propanone, ethyl 2,4,6-trimethylbenzoylphenylphosphonate and 2-hydroxy-2-methyl-1-phenylpropanone.

[0036] In a preferred embodiment, the catalyst content is 0.5 to 3 wt%, based on the weight percentage of the isocyanate compound. The catalyst content includes, but is not limited to, the above range, and limiting it within the above range is beneficial to improving the curing reaction efficiency.

[0037] To further improve the efficiency of the curing reaction, the catalyst is preferably, but not limited to, organotin compounds, more preferably stannous octoate and / or dibutyltin dilaurate.

[0038] In a preferred embodiment, the solid content of the slurry is 5-10 wt%. The solid content of the slurry includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improving the coatability of the slurry, thereby better utilizing the functions of the first modified layer 21 and the second modified layer 22, and further beneficial to improving the tensile strength and interlayer bonding force of the negative electrode composite current collector, and suppressing the peeling and detachment of the first conductive layer 31 and the second conductive layer 32.

[0039] To improve the dispersibility of the raw materials, preferably, the solvent includes, but is not limited to, one or more of the group consisting of toluene, ethyl acetate and acetone.

[0040] In order to improve the curing reaction effect, thereby better utilizing the functions of the first modified layer 21 and the second modified layer 22, and further improving the tensile strength and interlayer bonding force of the negative electrode composite current collector, and suppressing the peeling and detachment of the first conductive layer 31 and the second conductive layer 32, in a preferred embodiment, an ultraviolet light source is used to provide ultraviolet light irradiation conditions during the curing reaction. The power of the ultraviolet light source is 1000-1500W, and the curing reaction time is 15-60s.

[0041] In a preferred embodiment, the thicknesses of the first modified layer 21 and the second modified layer 22 are independently, but not limited to, 0.2–1 μm. Compared to other ranges, limiting the thicknesses of the first modified layer 21 and the second modified layer 22 to the above ranges is beneficial for better utilizing the functions of the first modified layer 21 and the second modified layer 22, thereby improving the tensile strength of the negative electrode composite current collector and the interlayer bonding force, and suppressing the peeling and detachment of the first conductive layer 31 and the second conductive layer 32.

[0042] In a preferred embodiment, the thickness of the substrate layer 10 is 2–12 μm. Compared to other ranges, limiting the thickness of the substrate layer 10 to the above range is beneficial for reducing the weight of the negative electrode composite current collector and improving its flexibility. To further reduce its weight and further improve its flexibility, the thickness of the substrate layer 10 is preferably 2–6.5 μm, more preferably 2.4–4.5 μm.

[0043] In a preferred embodiment, the thicknesses of the first conductive layer 31 and the second conductive layer 32 are independently limited to, but not limited to, 0.1–1.51 μm. Compared to other ranges, limiting the thicknesses of the first conductive layer 31 and the second conductive layer 32 to the above ranges is beneficial to improving the conductivity of the negative electrode composite current collector.

[0044] In a preferred embodiment, the first conductive layer 31 and the second conductive layer 32 are each independently including, but not limited to, a copper layer. The aforementioned type of first conductive layer 31 and second conductive layer 32 is suitable for negative electrode composite current collectors.

[0045] To further improve the bonding strength between the first modified layer 21 and the first conductive layer 31, and between the second modified layer 22 and the second conductive layer 32, such as Figure 2 As shown, in a preferred embodiment, a first metal oxide layer 41 is further disposed between the first modified layer 21 and the first conductive layer 31, and a second metal oxide layer 42 is further disposed between the second modified layer 22 and the second conductive layer 32.

[0046] To further improve the bonding force between the first modified layer 21 and the first conductive layer 31, and between the second modified layer 22 and the second conductive layer 32, preferably, the thicknesses of the first metal oxide layer 41 and the second metal oxide layer 42 are independently, but not limited to, 0.01 to 0.1 μm.

[0047] In a preferred embodiment, the first metal oxide layer 41 and the second metal oxide layer 42 are each independently including, but not limited to, a copper oxide layer. The aforementioned first metal oxide layer 41 and second metal oxide layer 42 are suitable for negative electrode composite current collectors.

[0048] The negative electrode composite current collector provided in this application exhibits excellent bonding properties between its layers, especially the wet bonding strength after immersion at 85°C for 30 days. 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 3–10 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 3–7 N / 15 mm.

[0049] The negative electrode composite current collector provided in this application exhibits excellent tensile strength in both the MD and TD directions. In a preferred embodiment, the tensile strength of the negative electrode composite current collector is ≥200MPa in the MD direction and ≥170MPa in the TD direction.

[0050] The second aspect of this application also provides a method for preparing the above-mentioned negative electrode composite current collector provided in this application. The method for preparing the negative 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 negative electrode composite current collector.

[0051] 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 negative electrode composite current collector has excellent tensile strength, excellent interlayer bonding force, and good heat resistance.

[0052] 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.

[0053] 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.

[0054] To improve the bonding force between the first conductive layer 31 and the first modified layer 21, and between the second conductive layer 32 and the second modified layer 22, and to facilitate the preparation of the first conductive layer 31 and the second conductive layer 32, preferably, between steps S-A2 and S-A3, a first metal oxide layer 41 is deposited on the surface of the first modified layer 21 away from the substrate layer 10, and a second metal oxide layer 42 is deposited on the surface of the second modified layer 22 away from the substrate layer 10.

[0055] In a preferred embodiment, the first metal oxide layer 41 and the second metal oxide layer 42 are deposited by sputtering. Depositing the first metal oxide layer 41 and the second metal oxide layer 42 using the above method facilitates control over the thickness and density of the deposited layers, thereby improving the adhesion of the subsequently formed first conductive layer 31 and second conductive layer 32.

[0056] Preferably, the process parameters for the sputtering deposition process include: vacuum degree ≥10 -3 Pa, main roller temperature is -25~35℃, main roller speed is ≤20m / min, and sputtering power is ≤20kW.

[0057] 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 negative electrode includes the aforementioned negative electrode composite current collector and a negative electrode active material disposed on the surface of the negative electrode composite current collector. The aforementioned negative electrode composite current collector provided by this application exhibits strong interlayer bonding (dry and wet bonding), and excellent tensile strength and heat resistance. Applying the aforementioned negative electrode composite current collector to lithium-ion batteries can improve the electrochemical performance and lifespan of lithium-ion batteries.

[0058] 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.

[0059] Example 1

[0060] A method for preparing a negative electrode composite current collector, comprising:

[0061] (1) A BOPP film with a thickness of 4.5 μm was subjected to corona treatment under 3000W conditions, and the treated BOPP film was put into use.

[0062] (2) Dissolve 3g of diphenylmethane diisocyanate, 5g of acrylic acid and 3g of thiourea in 86.16g of toluene to prepare solution A. Dissolve 0.15g of 2-hydroxy-2-methyl-1-phenyl-1-propanone and 0.09g of stannous octoate in 15g of toluene to prepare solution B. Add the prepared solution B to solution A and mix. Then, perform ultrasonic and mechanical stirring. Stir at 120 rpm at 80°C for 8 hours to obtain a mixed system. The solid content of the mixed system is 10 wt%.

[0063] (3) The mixed system obtained in step (2) is coated on the upper and lower surfaces of the corona-treated BOPP film using a micro-gravure coating machine (Kejing, MSK-AFA-MG200). After curing under 1000W ultraviolet light for 30s, 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.

[0064] (4) A copper oxide layer is sputtered on the surface of the first modified layer 21 away from the substrate layer 10 to form a first metal oxide layer 41, and a copper oxide layer is sputtered on the surface of the second modified layer 22 away from the substrate layer 10 to form a second metal oxide layer 42, thereby obtaining a second stacked structure; wherein, during the sputtering process, the vacuum degree is ≥10 -3 Pa, main roller temperature is 5℃, main roller speed is 10m / min, sputtering power is 13.3kW;

[0065] (5) Copper is deposited on the side of the first metal oxide layer 41 away from the substrate layer 10 by electron gun evaporation to form the first conductive layer 31, and copper is deposited on the side of the second metal oxide layer 42 away from the substrate layer 10 to form the second conductive layer 32, thus obtaining the negative electrode composite current collector; wherein, during the evaporation process, the temperature of the main roller is -20℃, the film forming speed is 10m / min, and the bias voltage is 450V.

[0066] The negative electrode composite current collector prepared in Example 1 has Figure 2 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.

[0067] Example 2

[0068] The difference from Example 1 is that step (4) is omitted, and step (5) includes: depositing copper on the surface of the first modified layer 21 away from the substrate layer 10 to form the first conductive layer 31, depositing copper on the surface of the second modified layer 22 away from the substrate layer 10 to form the second conductive layer 32, and obtaining the negative electrode composite current collector. The process parameters of the evaporation process in step (5) are the same as those in Example 1.

[0069] Example 3

[0070] The difference from Example 1 is that the amount of diphenylmethane diisocyanate is changed so that it accounts for 1 wt% of the total weight of the slurry; and the amount of stannous octoate is 0.03 g.

[0071] The thickness of the first modified layer 21 and the second modified layer 22 in the prepared negative electrode composite current collector is 300 nm.

[0072] Example 4

[0073] The difference from Example 1 is that the amount of diphenylmethane diisocyanate was changed so that its weight percentage in the total slurry was 5 wt%.

[0074] The thickness of the first modified layer 21 and the second modified layer 22 in the prepared negative electrode composite current collector is 300 nm.

[0075] Example 5

[0076] The difference from Example 1 is that the amount of diphenylmethane diisocyanate was changed so that it accounted for 6 wt% of the total weight of the slurry.

[0077] The thickness of the first modified layer 21 and the second modified layer 22 in the prepared negative electrode composite current collector is 300 nm.

[0078] Example 6

[0079] The difference from Example 1 is that the content of acrylic acid is changed so that it accounts for 1 wt% of the total weight of the slurry; at the same time, the amount of 2-hydroxy-2-methyl-1-phenyl-1-propanone is 0.03 g.

[0080] The thickness of the first modified layer 21 and the second modified layer 22 in the prepared negative electrode composite current collector is 300 nm.

[0081] Example 7

[0082] The difference from Example 1 is that the content of acrylic acid is changed so that it accounts for 6 wt% of the total weight of the slurry; at the same time, the amount of 2-hydroxy-2-methyl-1-phenyl-1-propanone used is 0.18 g.

[0083] The thickness of the first modified layer 21 and the second modified layer 22 in the prepared negative electrode composite current collector is 300 nm.

[0084] Example 8

[0085] The difference from Example 1 is that the content of thiourea is changed so that it accounts for 1 wt% of the total weight of the slurry.

[0086] The thickness of the first modified layer 21 and the second modified layer 22 in the prepared negative electrode composite current collector is 300 nm.

[0087] Example 9

[0088] The difference from Example 1 is that the content of thiourea is changed so that it accounts for 4 wt% of the total weight of the slurry.

[0089] The thickness of the first modified layer 21 and the second modified layer 22 in the prepared negative electrode composite current collector is 300 nm.

[0090] Example 10

[0091] The difference from Example 1 is that the curing reaction time is 15 seconds.

[0092] Example 11

[0093] The difference from Example 1 is that the curing reaction time is 60 seconds.

[0094] Example 12

[0095] The difference from Example 1 is that the curing reaction time is 100 seconds.

[0096] Comparative Example 1

[0097] The difference from Example 1 is that steps (2) and (3) are omitted, and copper is directly deposited on both sides of the corona-treated BOPP film.

[0098] Comparative Example 2

[0099] The difference from Example 2 is that steps (2) and (3) are omitted, and copper is directly deposited on both sides of the corona-treated BOPP film.

[0100] The sheet resistance of the negative 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 negative electrode composite current collector 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 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.

[0101] In all the embodiments and comparative examples of this application, a negative electrode active material layer was coated on the surface of the negative electrode composite current collector to obtain a layer disposed on its surface. The negative electrode active material was graphite, NCM811 was used as the positive electrode, a ceramic membrane was used as the separator, and a 1 mol / L LiPF6 electrolyte (solvents included DMC and DC) was used to assemble a lithium-ion battery. Lithium deposition and cycle stability were tested. The coulombic efficiency method was used to test lithium deposition. The cycle stability test conditions were: voltage range of 2.8V to 4.3V, 1C constant current charge-discharge. The test results are shown in Table 2.

[0102] Table 1

[0103]

[0104] Table 2

[0105] Internal resistance (mΩ) Number of turns required for discharge at room temperature to 80% capacity retention Example 1 10.61 1454 Example 2 9.77 1585 Example 3 12.41 1100 Example 4 14.32 989 Example 5 16.19 881 Example 6 13.33 1019 Example 7 18.49 654 Example 8 16.87 789 Example 9 19.21 598 Example 10 15.02 987 Example 11 12.16 1221 Example 12 13.33 912 Comparative Example 1 35.16 179 Comparative Example 2 32.18 221

[0106] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: A conventional negative electrode composite current collector includes a first conductive layer 31, a substrate layer 10, and a second conductive layer 32 stacked sequentially. The negative electrode composite current collector provided in this application further includes a first modified layer 21 disposed between the first conductive layer 31 and the substrate layer 10, and a second modified layer 22 disposed between the second conductive layer 32 and the substrate layer 10. The first modified layer 21 and the second modified layer 22 provided in this application are prepared using the specific method described above. The isocyanate compound includes aromatic groups, and the introduction of aromatic groups can improve the rigidity and tensile strength of the subsequently prepared first modified layer 21 and second modified layer 22. During the curing reaction, isocyanate compounds can bond with the modifier to form a cross-linked network structure. At the same time, the amino groups in the modifier (such as thiourea) can form coordination bonds with the metal elements in the first conductive layer 31 and the second conductive layer 32 to enhance the bonding force, thereby improving the bonding force between the first modified layer 21 and the first conductive layer 31, as well as the bonding force between the second modified layer 22 and the second conductive layer 32.

[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 negative electrode composite current collector, characterized by, The negative electrode composite current collector comprises: a substrate layer (10) whose material is biaxially oriented polypropylene; 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 isocyanate compounds, acrylic acid, a modifier, a photoinitiator, a catalyst and a solvent to obtain a slurry; wherein the isocyanate compounds comprise an aromatic group, and the modifier contains an amino group; Step S2, coating the slurry on the two side surfaces of the substrate layer (10) and performing a curing reaction under ultraviolet light irradiation to obtain the first modified layer (21) and the second modified layer (22).

2. The negative composite current collector according to claim 1, wherein The content of the isocyanate compounds is 1-5wt% based on the weight percentage of the slurry; Preferably, the isocyanate compounds are selected from diphenylmethane diisocyanate and / or toluene diisocyanate.

3. The negative composite current collector according to claim 1, wherein The content of the acrylic acid is 1-5wt% based on the weight percentage of the slurry; Preferably, the modifier is thiourea; More preferably, the modifier is thiourea, and the content of the thiourea is 1-3wt% based on the weight percentage of the slurry.

4. The negative composite current collector according to any one of claims 1 to 3, characterized in that, The content of the photoinitiator is 1-3wt% based on the weight percentage of the acrylic acid; Preferably, the photoinitiator is selected from one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-trimethylbenzoyl phenyl phosphinic acid ethyl ester and 2-hydroxy-2-methyl-1-phenylpropanone; Preferably, the content of the catalyst is 0.5-3wt% based on the weight percentage of the isocyanate compounds; Preferably, the catalyst is selected from organic tin compounds, and more preferably is stannous octoate and / or dibutyltin dilaurate.

5. The negative composite current collector according to claim 4, wherein The solid content of the slurry is 5-10wt%; Preferably, the solvent is selected from one or more of toluene, ethyl acetate and acetone; Preferably, in the process of the curing reaction, an ultraviolet light source is used to provide ultraviolet light irradiation, the power of the ultraviolet light source is 1000-1500W, and the curing reaction time is 15-60s.

6. The negative composite current collector of claim 1, wherein The thickness of the first modified layer (21) and the second modified layer (22) is independently selected from 0.2-1μm; Preferably, the thickness of the substrate layer (10) is 2-12μm, preferably 2-6.5μm, and more preferably 2.4-4.5μm; Preferably, the thickness of the first conductive layer (31) and the second conductive layer (32) is independently selected from 0.1-1.5 μm, respectively; Preferably, the first conductive layer (31) and the second conductive layer (32) are independently selected from copper layer, respectively.

7. The negative composite current collector of claim 1, wherein A first metal oxide layer (41) is further arranged between the first modified layer (21) and the first conductive layer (31), and a second metal oxide layer (42) is further arranged between the second modified layer (22) and the second conductive layer (32); Preferably, the thickness of the first metal oxide layer (41) and the second metal oxide layer (42) is independently selected from 0.01-0.1 μm, respectively; Preferably, the first metal oxide layer (41) and the second metal oxide layer (42) are independently selected from copper oxide layer, respectively.

8. The negative composite current collector of claim 1, wherein The dry adhesion between the substrate layer (10) and the first conductive layer (31) or the second conductive layer (32) is 3-10 N / 15 mm, and the wet adhesion 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 negative electrode composite current collector in the MD direction is ≥200 MPa, and the tensile strength in the TD direction is ≥170 MPa.

9. A method for producing the negative electrode composite current collector according to any one of claims 1 to 8, characterized by, The preparation method of the negative 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 negative 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 negative electrode comprises the negative electrode composite current collector according to any one of claims 1-8 and a negative electrode active material arranged on the surface of the negative electrode composite current collector.

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