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 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 an organic compound containing one or more of ureido, amino and acylamino, a cellulose ether compound, a transition metal oxide, a silane coupling agent and a solvent to obtain a mixed system; and S2, coating the surfaces of the two sides of the base material layer with the mixed system, 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 batteries, in particular to a negative 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 a lithium ion battery, which functions to carry active materials and collect and conduct electrons. An ideal lithium ion battery current collector should meet the following requirements: (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) inexpensive and easy to obtain; (6) light weight.

[0003] Traditional current collectors are generally aluminum foils for positive electrode current collectors and copper foils for negative electrode current collectors. However, copper foils and aluminum foils 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] The existing document (publication number CN113795954A) discloses a composite current collector, which comprises a polymer film layer and a metal layer arranged on at least one surface of the polymer film layer; a first coating layer is arranged between the polymer film layer and the metal layer, and a second coating layer is arranged between the first coating layer and the metal layer; the adhesion between the first coating layer and the second coating layer is greater than the adhesion between the second coating layer and the metal layer, and greater than the adhesion between the first coating layer and the polymer film layer, thereby effectively improving the adhesion between the metal layer and the polymer film layer.

[0005] However, the composite current collector 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 low, which easily causes the risk of peeling or falling off of the metal layer from the polymer film layer; and no electrolyte immersion data is provided, while the true test of the adhesion of the current collector is the wet adhesion after electrolyte immersion; (2) in the evaporation process, due to the high energy of the evaporation particles, the surface of the polymer film is heated to a temperature exceeding the glass transition temperature of the film, causing the polymer macromolecular chain to move and recrystallize, forming crystalline internal stress, which causes the polymer film to appear scalding or shrinkage, ultimately affecting the appearance of the product and subsequent cell process.

[0006] On this basis, it is particularly important to research and develop a negative electrode composite current collector with excellent heat resistance and wet adhesion. SUMMARY

[0007] The main objective of this invention is to provide a negative electrode composite current collector, its preparation method, and a lithium-ion battery, so as to solve the problem that the existing negative electrode composite current collector is difficult to have both excellent heat resistance and poor adhesion between the metal layer and the polymer film after electrolyte immersion.

[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 an organic polymer material. 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 modified layer and the second modified layer comprises: step S1, mixing one or more organic compounds containing urea, amino, and amide groups, cellulose ether compounds, transition metal oxides, silane coupling agents, and solvents to obtain a mixed system; step S2, coating the mixed system onto both sides of the substrate layer, and obtaining the first modified layer and the second modified layer after a curing reaction.

[0009] Further, the organic compound containing one or more of urea, amino, and amide groups is selected from dihydroxymethylurea and / or hydroxymethylurea; preferably, the content of the organic compound is 5 to 20 wt% based on the weight percentage of the mixed system.

[0010] Furthermore, the solid content of the mixed system is 5–10 wt%.

[0011] Further, the content of cellulose ether compounds is 0.1 to 1 wt% based on the weight percentage of the mixed system; preferably, the cellulose ether compounds are selected from one or more of the group consisting of carboxymethyl cellulose, carboxyethyl cellulose and hydroxypropyl cellulose; preferably, when the cellulose ether compound is carboxymethyl cellulose, the weight average molecular weight of carboxymethyl cellulose is 15,000 to 30,000.

[0012] Further, the content of the transition metal oxide is 0.5 to 1 wt% based on the weight percentage of the mixed system; preferably, the transition metal oxide is selected from one or more of the group consisting of silica sol, titanium dioxide and nano alumina; preferably, the D50 of the transition metal oxide is 15 to 25 nm.

[0013] Further, the weight ratio of the silane coupling agent to the transition metal oxide is (10-30):100; preferably, the silane coupling agent is selected from one or more of the group consisting of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane and γ-(methacryloyloxy)propyltrimethoxysilane.

[0014] Furthermore, the mixed system also includes a catalyst; preferably, the weight ratio of the catalyst to the organic compound is (1-5):100; preferably, the catalyst is selected from one or more of the group consisting of magnesium chloride, aluminum chloride and zinc chloride.

[0015] Furthermore, in step S1, the mixing is carried out under stirring conditions, with a stirring speed of 115–135 rpm / min.

[0016] Furthermore, step S3 involves a coating process using a micro-recessed coating method.

[0017] Furthermore, the curing reaction temperature is 50–100°C, and the time is 1–10 min.

[0018] 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.

[0019] Furthermore, the thicknesses of the first metal oxide layer and the second metal oxide layer are each independently selected from 3 to 10 nm; preferably, the first metal oxide layer and the second metal oxide layer are each independently selected from copper oxide layers.

[0020] Furthermore, the thickness of the substrate layer is 2 to 12 μm, preferably 2 to 6.5 μm, and more preferably 2.4 to 4.5 μm.

[0021] Furthermore, the thicknesses of the first modified layer and the second modified layer are independently selected from 0.2 to 1 μm.

[0022] Furthermore, the thicknesses of the first conductive layer and the second conductive layer are independently selected from 0.1 to 1.51 μm.

[0023] Furthermore, the material of the substrate layer is selected from one or more of the group consisting of polyethylene, biaxially oriented polypropylene, polyethylene terephthalate, polyethylene terephthalate, poly(p-phenylene terephthalate), polyimide, polycarbonate, polyetheretherketone, polyoxymethylene, polyphenylene sulfide, poly(p-phenylene ether), polyvinyl chloride, polyamide, and polytetrafluoroethylene.

[0024] Furthermore, the first conductive layer and the second conductive layer are each independently selected from the copper layer.

[0025] Furthermore, the dry bonding force between the substrate layer and the first conductive layer or the second conductive layer is 5 to 10 N / 15 mm; preferably, the wet bonding force between the substrate layer and the first conductive layer or the second conductive layer is 2 to 7 N / 15 mm; preferably, after being treated at 150°C for 30 min, the thermal shrinkage rate of the negative electrode composite current collector in the MD direction is ≤3%, and the thermal shrinkage rate in the TD direction is ≤1%.

[0026] 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.

[0027] 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.

[0028] By applying the technical solution of this invention, the organic compounds containing the specific groups in the first and second modified layers provided in this application can form coordination bonds between the specific groups and materials (such as copper) in the first and second conductive layers, and place them between the substrate layer and the first or second conductive layer. This significantly improves the bonding force between the layers in the negative electrode composite current collector, reduces the risk of the first or second conductive layer detaching, and improves its peel strength, especially significantly improving its wet bonding force after immersion in electrolyte, thereby increasing its service life. Simultaneously, the introduction of cellulose ether compounds can act as a reinforcing agent and heat-resistant agent, thereby improving the heat resistance of the negative electrode composite current collector, suppressing thermal deformation caused by temperature rise, and thus improving the service life of the lithium-ion battery. Furthermore, the introduction of transition metal oxides can act as heat-resistant agents, thereby improving the heat resistance of the negative electrode composite current collector. The introduction of silane coupling agents facilitates subsequent curing reactions, thereby improving the bonding force between the first and second modified layers and the substrate layer. Attached Figure Description

[0029] 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:

[0030] 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;

[0031] 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.

[0032] The above figures include the following reference numerals:

[0033] 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

[0034] 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.

[0035] As described in the background section, existing negative electrode composite current collectors suffer from the problem of simultaneously possessing excellent heat resistance and poor adhesion between the metal layer and the polymer film after electrolyte immersion. To address these 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 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 one or more organic compounds containing urea, amino, and amide groups, cellulose ether compounds, transition metal oxides, silane coupling agents, and solvents to obtain a mixed system; step S2, coating the mixed system 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.

[0036] The organic compounds containing the specific groups in the first modified layer 21 and the second modified layer 22 provided in this application can form coordination bonds between the specific groups and materials (such as copper) in the first conductive layer 31 and the second conductive layer 32, and place them between the substrate layer 10 and the first conductive layer 31 or the second conductive layer 32. This significantly improves the bonding force between the layers in the negative electrode composite current collector, reduces the risk of the first conductive layer 31 or the second conductive layer 32 detaching, and improves its peel strength. In particular, it significantly improves its wet bonding force after immersion in electrolyte, thereby improving its service life. Simultaneously, the introduction of cellulose ether compounds can act as a reinforcing agent and heat-resistant agent, thereby improving the heat resistance of the negative electrode composite current collector, suppressing thermal deformation caused by temperature rise, and thus improving the service life of the lithium-ion battery. Furthermore, the introduction of transition metal oxides can act as heat-resistant agents, thereby improving the heat resistance of the negative electrode composite current collector. The introduction of silane coupling agents facilitates subsequent curing reactions, thereby improving the bonding force between the first modified layer 21 and the second modified layer 22 and the substrate layer 10.

[0037] In a preferred embodiment, the solid content of the mixture is 5-10 wt%. Compared to other ranges, limiting the solid content of the mixture to the above range facilitates coating treatment and improves its processability.

[0038] In a preferred embodiment, the organic compound containing one or more of urea, amino, and amide groups includes, but is not limited to, dihydroxymethylurea and / or hydroxymethylurea. Compared to other types, using the above-mentioned organic compounds is beneficial to improving the adhesion between the substrate layer 10 and the first conductive layer 31 or the second conductive layer 32, thereby reducing the risk of the first conductive layer 31 or the second conductive layer 32 detaching, and thus helping to extend the service life of the lithium-ion battery.

[0039] To further improve the adhesion between the substrate layer 10 and the first conductive layer 31 or the second conductive layer 32, and to further improve the service life of the lithium-ion battery, preferably, the content of organic compounds is 5 to 20 wt% based on the weight percentage of the mixed system.

[0040] In a preferred embodiment, the content of cellulose ether compounds is 0.1 to 1 wt% of the weight percentage of the mixed system. The content of cellulose ether compounds includes, but is not limited to, the above range. Limiting it to the above range is beneficial to better utilize the role of cellulose ether compounds as reinforcing agents and heat-resistant agents, thereby improving the heat resistance of the negative electrode composite current collector and reducing its thermal deformation.

[0041] To further improve the heat resistance of the negative electrode composite current collector and further reduce its thermal deformation, preferably, the cellulose ether compound includes, but is not limited to, one or more of the group consisting of carboxymethyl cellulose, carboxyethyl cellulose and hydroxypropyl cellulose.

[0042] To further improve the heat resistance of the negative electrode composite current collector and further reduce its thermal deformation, preferably, when the cellulose ether compound is carboxymethyl cellulose, the weight-average molecular weight of carboxymethyl cellulose is 15,000 to 30,000.

[0043] In a preferred embodiment, the content of transition metal oxides is 0.5 to 1 wt% of the weight percentage of the mixed system. The content of transition metal oxides includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improving the heat resistance of the substrate and increasing the bonding sites, thereby improving the heat resistance of the negative electrode composite current collector and the bonding force between the layers.

[0044] To further improve the bonding force between the layers in the negative electrode composite current collector, preferably, the transition metal oxide includes, but is not limited to, one or more of the group consisting of silica sol, titanium dioxide and nano-alumina.

[0045] To further improve the heat resistance of the negative electrode composite current collector, preferably, the D50 of the transition metal oxide is 15-25 nm.

[0046] In a preferred embodiment, the weight ratio of the silane coupling agent to the transition metal oxide is (10-30):100. The weight ratio of the silane coupling agent to the transition metal oxide includes, but is not limited to, the above range. Limiting it to this range is beneficial for increasing the curing and crosslinking reaction rate of the first modified layer 21 and the second modified layer 22, and for improving the dispersibility of the transition metal oxide, thereby improving the overall performance of the negative electrode composite current collector, such as the bonding force and heat resistance between the layers.

[0047] To further improve the curing and crosslinking reaction rate, and to further improve the mechanical strength of the first modified layer 21 and the second modified layer 22, as well as the adhesion between the layers in the negative electrode composite current collector, preferably, the silane coupling agent includes, but is not limited to, one or more of the group consisting of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560), and γ-(methacryloyloxy)propyltrimethoxysilane.

[0048] The introduction of a catalyst can improve the reaction efficiency of the curing reaction. In a preferred embodiment, the mixture also includes a catalyst.

[0049] In a preferred embodiment, the weight ratio of the catalyst to the organic compound is (1-5):100. The weight ratio of the catalyst to the organic compound includes, but is not limited to, the above range. Limiting it to this range is beneficial for improving the reaction efficiency of the curing reaction, providing more favorable conditions for the subsequent coating process and curing reaction of the mixed system.

[0050] To further improve the reaction efficiency of the curing reaction, preferably, the catalyst includes, but is not limited to, one or more of the group consisting of magnesium chloride, aluminum chloride, and zinc chloride.

[0051] To further improve the efficiency of the curing reaction, preferably, the mixing in step S1 is carried out under stirring conditions, with a stirring speed of 115-135 rpm / min.

[0052] Microgravure coating is a contact coating method. In a preferred embodiment, step S3 involves coating using microgravure coating. This coating method improves processing efficiency and allows for easy control of coating thickness.

[0053] In a preferred embodiment, the curing reaction temperature is 50–100°C, and the time is 1–10 min. The curing reaction temperature and time include, but are not limited to, the above ranges. Limiting them to the above ranges is beneficial to improving the curing reaction efficiency, improving the adhesion of each layer in the negative electrode composite current collector, and improving the overall performance of the negative electrode composite current collector, such as its heat resistance and mechanical properties.

[0054] In a preferred embodiment, such as Figure 2 As shown, 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. The presence of the first metal oxide layer 41 and the second metal oxide layer 42 helps to improve the adhesion 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, and also facilitates the preparation of the first conductive layer 31 and the second conductive layer 32.

[0055] To further improve the adhesion 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, 3 to 10 nm.

[0056] 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.

[0057] In a preferred embodiment, the thickness of the substrate layer 10 is 2–12 μm. The thickness of the substrate layer 10 includes, but is not limited to, the above range. Limiting it within this range helps reduce the weight of the negative electrode composite current collector and also improves its flexibility. To further reduce the weight of the negative electrode composite current collector, the thickness of the substrate layer 10 is preferably 2–6.5 μm, more preferably 2.4–4.5 μm.

[0058] 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 to improving the bonding strength between the substrate layer 10 and the first conductive layer 31 and between the substrate layer 10 and the second conductive layer 32, especially the wet bonding strength of the negative electrode composite current collector after being immersed in the electrolyte.

[0059] 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.

[0060] In a preferred embodiment, the material of the substrate layer 10 includes, but is not limited to, one or more of the group consisting of polyethylene, biaxially oriented polypropylene, polyethylene terephthalate, polyethylene terephthalate, poly(p-phenylene terephthalate), polyimide, polycarbonate, polyetheretherketone, polyoxymethylene, polyphenylene sulfide, poly(p-phenylene ether), polyvinyl chloride, polyamide, and polytetrafluoroethylene. Compared to other types, using the above-mentioned substrate layer 10 helps to reduce the weight of the negative electrode composite current collector itself, and also helps to improve its flexibility. When the lithium-ion battery is impacted by a foreign object, the substrate layer 10 can wrap the fracture surface, thereby preventing the fracture from piercing the separator and causing a short circuit, thus improving the safety performance of the battery.

[0061] 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.

[0062] 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 minutes. 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 5–10 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 2–7 N / 15 mm.

[0063] The negative electrode composite current collector provided in this application exhibits excellent heat resistance, with extremely low thermal shrinkage after treatment at 150°C for 30 minutes. In a preferred embodiment, after treatment at 150°C for 30 minutes, the thermal shrinkage rate of the negative electrode composite current collector is ≤3% in the MD direction (longitudinal) and ≤1% in the TD direction (transverse).

[0064] 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.

[0065] 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 adhesion and heat resistance.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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 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.

[0072] 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.

[0073] Example 1

[0074] A method for preparing a negative electrode composite current collector, comprising:

[0075] (1) A PET film with a thickness of 4.5 μm was subjected to corona treatment at 3000 W and the treated PET film was put into use.

[0076] (2) 10g of dihydroxymethylurea, 0.5g of carboxymethyl cellulose (weight average molecular weight of 20000), and 0.1g of magnesium chloride were dissolved in 57.1g of water to prepare solution A. 1g of nano-silica sol (where the D50 of silica is 15nm) and 0.3g of γ-aminopropyltriethoxysilane were dissolved in 50g of water to prepare solution B. The above-prepared solutions A and B were mixed and subjected to ultrasonic and mechanical stirring. The mixture was stirred at 45℃ and 115rpm / min for 8h to obtain a mixed system. The solid content of the mixed system was 10wt%.

[0077] (3) The mixture 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 100°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 sequentially.

[0078] (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;

[0079] (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 5°C, the film forming speed is 10m / min, and the bias voltage is 450V.

[0080] The negative electrode composite current collector prepared in Example 1 has the following properties: Figure 2 The structure shown has the following characteristics: the thickness of the first modified layer 21 and the second modified layer 22 is 200 nm, the thickness of the first metal oxide layer 41 and the second metal oxide layer 42 is 3 nm, and the thickness of the first conductive layer 31 and the second conductive layer 32 is 1 μm.

[0081] Example 2

[0082] The difference from Example 1 is that the amount of dihydroxymethylurea was changed so that it accounted for 20 wt% of the mixture.

[0083] Example 3

[0084] The difference from Example 1 is that the amount of dihydroxymethylurea was changed so that it accounted for 3 wt% of the weight of the mixture.

[0085] Example 4

[0086] The difference from Example 1 is that the amount of carboxymethyl cellulose was changed so that it accounted for 0.5 wt% of the weight of the mixture.

[0087] Example 5

[0088] The difference from Example 1 is that the amount of carboxymethyl cellulose used is changed so that it accounts for 1 wt% of the weight of the mixture.

[0089] Example 6

[0090] The difference from Example 1 is that the amount of carboxymethyl cellulose was changed so that it accounted for 2 wt% of the weight of the mixture.

[0091] Example 7

[0092] The difference from Example 1 is that the amount of nano-silica sol was changed so that it accounted for 0.5 wt% of the weight of the mixture.

[0093] Example 8

[0094] The difference from Example 1 is that the amount of nano-silica sol was changed so that it accounted for 1 wt% of the weight of the mixture.

[0095] Example 9

[0096] The difference from Example 1 is that the amount of nano-silica sol was changed so that it accounted for 2 wt% of the weight of the mixture.

[0097] Example 10

[0098] The difference from Example 1 is that in step (3), the curing reaction temperature is 50°C and the time is 10 min.

[0099] Example 11

[0100] The difference from Example 1 is that in step (3), the curing reaction temperature is 100°C and the time is 1 min.

[0101] Comparative Example 1

[0102] The difference from Example 1 is that steps (2) and (3) are omitted, and the first metal oxide layer 41 (copper oxide layer) and the second metal oxide layer 42 (copper oxide layer) are directly sputtered on both sides of the corona-treated PET film.

[0103] Comparative Example 2

[0104] The difference from Example 1 is that steps (2) to (4) are omitted, and copper is directly deposited on both sides of the corona-treated PET film to form the first conductive layer 31 and the second conductive layer 32.

[0105] 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. After drying in an oven at 150°C for 30 min, the thermal shrinkage rate of the negative electrode composite current collector in the MD and TD directions was tested. 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 a dry environment and electrolyte immersion conditions (85°C, immersion for 3 days). The electrolyte used was a commercial electrolyte, model Hairong 9212. The test results are shown in Table 1.

[0106] 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.

[0107] Table 1

[0108]

[0109] Table 2

[0110] Lithiation Number of cycles required for discharge at room temperature to 80% capacity retention Example 1 No lithium precipitation 1750 Example 2 No lithium precipitation 1600 Example 3 No lithium precipitation 1533 Example 4 No lithium precipitation 1401 Example 5 No lithium precipitation 1333 Example 6 No lithium precipitation 1288 Example 7 No lithium precipitation 1200 Example 8 Slight lithium precipitation 1108 Example 9 Slight lithium precipitation 1091 Example 10 Slight lithium precipitation 1000 Example 11 Slight lithium precipitation 922 Comparative Example 1 Severe lithium precipitation 105 Comparative Example 2 Severe lithium precipitation 201

[0111] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: The organic compounds containing the specific groups in the first modified layer 21 and the second modified layer 22 provided in this application can form coordination bonds between the specific groups and the materials (such as copper) in the first conductive layer 31 and the second conductive layer 32, and place them between the substrate layer 10 and the first conductive layer 31 or the second conductive layer 32. This can significantly improve the bonding force between the layers in the negative electrode composite current collector, reduce the risk of the first conductive layer 31 or the second conductive layer 32 falling off, improve its peel strength, and especially significantly improve its wet bonding force after immersion in electrolyte, thereby improving its service life. At the same time, the introduction of cellulose ether compounds can play the role of reinforcing agent and heat resistant agent, thereby improving the heat resistance of the negative electrode composite current collector, suppressing thermal deformation caused by temperature rise, and thus improving the service life of lithium-ion batteries. In addition, the introduction of transition metal oxide nanoparticles can play the role of heat resistant agent, thereby improving the heat resistance of the negative electrode composite current collector.

[0112] As can be seen from Table 2 above, the lithium-ion batteries of Examples 1 to 11 of this application have a lower degree of lithium plating than those of Comparative Examples 1 and 2. This indicates that the lithium-ion batteries containing the above-mentioned negative electrode composite current collector prepared in each embodiment of this application have a longer service life than those of Comparative Examples 1 and 2.

[0113] The number of cycles required for the lithium-ion batteries prepared in Examples 1 to 11 of this application to discharge at room temperature to a capacity retention rate of 80% is significantly greater than that in Comparative Examples 1 and 2. This indicates that the lithium-ion batteries containing the above-mentioned negative electrode composite current collector prepared in each embodiment of this application have better cycle performance than Comparative Examples 1 and 2.

[0114] 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.

[0115] 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), a material of the substrate layer (10) being 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 one side surface of the first modified layer (21) away from the substrate layer (10); a second conductive layer (32) arranged on one side surface of the second modified layer (22) away from the substrate layer (10); a preparation method of the first modified layer (21) and the second modified layer (22) comprises: Step S1, mixing an organic compound containing one or more of urea groups, amino groups and amide groups, a cellulose ether compound, a transition metal oxide and a silane coupling agent with a solvent to obtain a mixed system; Step S2, coating the mixed system on both side surfaces of the substrate layer (10), and obtaining the first modified layer (21) and the second modified layer (22) after a curing reaction.

2. The negative composite current collector according to claim 1, wherein The organic compound containing one or more of urea groups, amino groups and amide groups is selected from dihydroxymethylurea and / or hydroxymethylurea; Preferably, the content of the organic compound is 5-20wt% based on the weight percentage of the mixed system; Preferably, the solid content of the mixed system is 5-10wt%.

3. The negative electrode composite current collector according to claim 1 or 2, characterized in that, The content of the cellulose ether compound is 0.1-1wt% based on the weight percentage of the mixed system; Preferably, the cellulose ether compound is selected from one or more of carboxymethyl cellulose, carboxyethyl cellulose and hydroxypropyl cellulose; Preferably, when the cellulose ether compound is carboxymethyl cellulose, the weight average molecular weight of the carboxymethyl cellulose is 15000-30000.

4. The negative composite current collector according to any one of claims 1 to 3, characterized in that, The content of the transition metal oxide is 0.5-1wt% based on the weight percentage of the mixed system; Preferably, the transition metal oxide is selected from one or more of silica sol, titanium dioxide and nano-aluminum oxide; Preferably, the D50 of the transition metal oxide is 15-25nm.

5. The negative composite current collector according to claim 4, wherein The weight ratio of the silane coupling agent to the transition metal oxide is (10-30):100; Preferably, the silane coupling agent is selected from one or more of γ-aminopropyl triethoxysilane, γ-(2,3-epoxypropoxy) propyl trimethoxysilane and γ-(methacryloyloxy) propyl trimethoxysilane.

6. The negative composite current collector according to claim 5, wherein The mixed system further comprises a catalyst; Preferably, the weight ratio of the catalyst to the organic compound is (1-5):100; Preferably, the catalyst is selected from one or more of magnesium chloride, aluminum chloride and zinc chloride.

7. The negative composite current collector according to claim 5 or 6, wherein The mixing in the step S1 is carried out under stirring, and the stirring speed is 115-135rpm / min; and / or, The coating process in the step S3 is carried out by micro-concave coating; and / or, The temperature of the curing reaction is 50-100℃, and the time is 1-10 min.

8. The negative composite current collector according to any one of claims 5 to 7, wherein The first metal oxide layer (41) is further arranged between the first modified layer (21) and the first conductive layer (31), and the 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 3-10 nm, respectively; Preferably, the first metal oxide layer (41) and the second metal oxide layer (42) are independently selected from a copper oxide layer, respectively; Preferably, the thickness of the substrate layer (10) is 2-12μm, preferably 2-6.5μm, more preferably 2.4-4.5μm; Preferably, the thickness of the first modified layer (21) and the second modified layer (22) is independently selected from 0.2-1μm, respectively; Preferably, the thickness of the first conductive layer (31) and the second conductive layer (32) is independently selected from 0.1-1.51μm, respectively; Preferably, the material of the substrate layer (10) is selected from one or more of the group consisting of polyethylene, biaxially oriented polypropylene, polyethylene terephthalate, polyethylene terephthalate, poly-p-phenyleneterephthalamide, polyimide, polycarbonate, polyether ether ketone, polyformaldehyde, poly-p-phenylene sulfide, poly-p-phenylene oxide, polyvinyl chloride, polyamide and polytetrafluoroethylene; Preferably, the first conductive layer (31) and the second conductive layer (32) are independently selected from a copper layer, respectively; Preferably, the dry adhesion between the substrate layer (10) and the first conductive layer (31) or the second conductive layer (32) is 5-10N / 15mm; Preferably, the wet adhesion between the substrate layer (10) and the first conductive layer (31) or the second conductive layer (32) is 2-7N / 15mm; Preferably, the thermal shrinkage rate of the negative electrode composite current collector in the MD direction is ≤3% and the thermal shrinkage rate in the TD direction is ≤1% after being treated at 150℃ for 30min.

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 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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