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. The base material layer is made of a polyester 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 the other side, away from the base material layer, of the second modified layer; a preparation method of the first modified layer and the second modified layer comprises the following steps: S1, mixing chitosan, guar gum, an ester-based protective agent, a coupling agent and a solvent to obtain a mixed system; and S2, coating two side surfaces of a base material layer with the mixed system, and carrying out a curing reaction 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, serving 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 bonding 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, and the metal layer is easy to peel off or fall off from the polymer film layer; (2) the substrate used for current collectors, especially PET film, is easily corroded and degraded in electrolyte immersion, which seriously affects the safety and service life of the battery cell.

[0005] Therefore, it is necessary to research and develop a negative electrode composite current collector with excellent corrosion resistance and a metal layer that is not easily peeled or detached from the polymer film. Summary of the Invention

[0006] 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 problems of poor bonding force between the metal layer and the polymer film layer in the prior art negative electrode composite current collector, poor corrosion resistance, and easy peeling or detachment of the metal layer from the polymer film layer after being immersed in electrolyte.

[0007] 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 polyester 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 other 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 chitosan, guar gum, ester group protectant, coupling agent, and solvent to obtain a mixed system; step S2, coating the mixed system on both sides of the substrate layer, and obtaining the first modified layer and the second modified layer after a curing reaction.

[0008] Furthermore, the weight-average molecular weight of chitosan is 15,000 to 20,000; preferably, the weight percentage of chitosan in the mixture is 1 to 5 wt%.

[0009] Furthermore, the weight-average molecular weight of guar gum is 200,000 to 300,000; preferably, the weight percentage of guar gum in the mixture is 0.1 to 1 wt%.

[0010] Further, the weight percentage of the ester-protecting agent in the mixed system is 1-5 wt%; preferably, the weight percentage of the coupling agent in the mixed system is 5-7.5 wt%; more preferably, the ester-protecting agent is selected from one or more of the group consisting of trimethylsilyl ethanol ester, triphenylmethyl diphenylsilane and methoxymethyl ether; more preferably, the coupling agent is selected from titanate coupling agents, and more preferably one or more of the group consisting of isopropyl di(methacryloyl)isostearoyl titanate, isopropyl tri(dioctylphosphoyloxy)phthalate and isopropyl dioleoyloxy(dioctylphosphoyloxy)phthalate; more preferably, the solvent is selected from one or more of the group consisting of N,N-dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone.

[0011] Further, the solid content of the mixture is 5-10 wt%, and the viscosity is 100-200 mPa·s; preferably, the mixing in step S1 is carried out under ultrasonic and / or stirring conditions; preferably, the ultrasonic power is 100-300 W; preferably, the stirring speed is 110-140 rpm / min.

[0012] Furthermore, in step S3, a micro-recessed coating method is used for coating.

[0013] Furthermore, the curing reaction temperature is 50–100°C, and the time is 1–10 min.

[0014] Furthermore, the weight ratio of chitosan, guar gum, ester protectant and coupling agent is (1-5):0.1:(1-5):(5-7.5).

[0015] 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.

[0016] Furthermore, the thicknesses of the first metal oxide layer and the second metal oxide layer are independently selected from 1 to 10 nm.

[0017] Furthermore, the first metal oxide layer and the second metal oxide layer are each independently selected from the copper oxide layer.

[0018] Further, the thickness of the substrate layer is 2 to 6.5 μm, more preferably 2.4 to 4.5 μm; preferably, the material of the substrate layer is selected from one or more of the group consisting of polyethylene terephthalate, polyethylene terephthalate and polycarbonate.

[0019] Furthermore, the thicknesses of the first modified layer and the second modified layer are independently selected from 0.2 to 1 μm.

[0020] Furthermore, the thicknesses of the first conductive layer and the second conductive layer are independently selected from 0.1 to 1.51 μm; preferably, the first conductive layer and the second conductive layer are independently selected from copper layers.

[0021] 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, 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.

[0022] 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.

[0023] 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.

[0024] By applying the technical solution of this invention, chitosan contains a large number of amino groups. After coating the mixed system containing amino groups onto both sides of the substrate layer to form a first modified layer and a second modified layer, it can bond with materials (such as copper) in the first or second conductive layer, thereby improving the bonding force between the substrate layer and the first and second conductive layers. This reduces the risk of peeling or detachment of the first and second conductive layers, improving the structural stability of the negative electrode composite current collector. Simultaneously, the ester-based protective agent in the mixed system contains silicone protective groups, which can effectively inhibit the acid or alkali hydrolysis of the ester groups in the polyester material, thereby protecting the ester-containing substrate layer from electrolyte degradation and improving the corrosion resistance of the negative electrode composite current collector. Furthermore, the introduction of guar gum as a thickener into the mixed system, combined with the chitosan and ester-based protective agent, facilitates their synergistic effect, thereby improving the bonding force between the layers in the negative electrode composite current collector and its resistance to electrolyte corrosion, thus extending the service life of the negative electrode composite current collector. Attached Figure Description

[0025] 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:

[0026] 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;

[0027] 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.

[0028] The above figures include the following reference numerals:

[0029] 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

[0030] 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.

[0031] As described in the background section, existing negative electrode composite current collectors suffer from poor adhesion between the metal layer and the polymer film layer, as well as poor corrosion resistance. After immersion in electrolyte, the metal layer is easily peeled off or detached from the polymer film layer. To address these technical problems, this application provides a negative electrode composite current collector, such as... Figure 1As 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 polyester. 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 other 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 chitosan, guar gum, an ester protective agent, a coupling agent, and a solvent 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.

[0032] Chitosan contains a large number of amino groups. After coating the two sides of the substrate layer 10 with a mixture containing amino groups to form the first modified layer 21 and the second modified layer 22, it can bond with materials (such as copper) in the first conductive layer 31 or the second conductive layer 32. This improves the bonding force between the substrate layer 10 and the first and second conductive layers 31 and 32, thereby reducing the risk of peeling or detachment of the first and second conductive layers 31 and improving the structural stability of the negative electrode composite current collector. Simultaneously, the ester-based protective agent in the mixture contains silicone protective groups, which can effectively inhibit the acid or alkali hydrolysis of the ester groups in the polyester material, thus protecting the ester-containing substrate layer 10 from electrolyte degradation and improving the corrosion resistance of the negative electrode composite current collector. Furthermore, the introduction of guar gum as a thickener into the mixture, combined with chitosan and the ester-based protective agent, facilitates their synergistic effect, thereby improving the bonding force between the layers in the negative electrode composite current collector and its resistance to electrolyte corrosion, thus extending the service life of the negative electrode composite current collector.

[0033] In a preferred embodiment, the weight-average molecular weight of chitosan is 15,000 to 20,000. Compared to other ranges, using the above-mentioned type of chitosan is beneficial to improving the bonding force between the substrate layer 10 and the first conductive layer 31 and the second conductive layer 32, and to reducing the risk of peeling or detachment of the first conductive layer 31 and the second conductive layer 32, thereby improving the structural stability of the negative electrode composite current collector.

[0034] To further improve the bonding force between the substrate layer 10 and the first conductive layer 31 and the second conductive layer 32, preferably, the weight percentage of chitosan in the mixture is 1 to 5 wt%.

[0035] In a preferred embodiment, the weight-average molecular weight of guar gum is 200,000 to 300,000. Compared to other ranges, limiting the weight-average molecular weight of guar gum to the above range facilitates the adjustment of the viscosity of the mixture, thereby facilitating coating processes.

[0036] To further improve the bonding strength between layers and the resistance to electrolyte corrosion in the negative electrode composite current collector, and to facilitate coating processing, preferably, the weight percentage of guar gum in the mixture is 0.1 to 1 wt%.

[0037] In a preferred embodiment, the weight percentage of the ester-based protective agent in the mixture is 1–5 wt%. The weight percentage of the ester-based protective agent in the mixture includes, but is not limited to, the above range. Limiting it to this range is beneficial for better protecting the PET substrate from electrolyte degradation, thereby improving the corrosion resistance of the negative electrode composite current collector.

[0038] To further improve the resistance of PET substrate to electrolyte degradation, thereby further improving the corrosion resistance of the negative electrode composite current collector, preferably, the ester-based protective agent includes, but is not limited to, one or more of the group consisting of trimethylsilyl ethanol ester (TMSE), triphenylmethyl diphenylsilane, and methoxymethyl ether.

[0039] In a preferred embodiment, the weight percentage of the coupling agent in the mixed system is 5 to 7.5 wt%. The weight percentage of the coupling agent in the mixed system includes, but is not limited to, the above range. Limiting it to the above range is beneficial to increasing the crosslinking density of the first modified layer 21 and the second modified layer 22 obtained by the subsequent curing reaction, thereby improving the tensile strength and other mechanical properties of the negative electrode composite current collector.

[0040] In order to further improve the crosslinking density of the first modified layer 21 and the second modified layer 22, thereby further improving the tensile strength and other mechanical properties of the negative electrode composite current collector, preferably, the coupling agent includes, but is not limited to, titanate coupling agents, and more preferably, one or more of the group consisting of isopropyl di(methacryloyl)isostearyl titanate, isopropyl tri(dioctylphosphoyloxy)phthalate and isopropyl dioleoyloxy(dioctylphosphoyloxy)phthalate.

[0041] In a preferred embodiment, the solvent includes, but is not limited to, one or more of the group consisting of N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone. Compared to other types, using the above-mentioned solvents is beneficial for improving the dispersibility and compatibility of the components in the mixture.

[0042] In a preferred embodiment, the solid content of the mixture is 5–10 wt%, and the viscosity is 100–200 mPa·s. Compared to other ranges, limiting the solid content and viscosity of the mixture to the above ranges facilitates coating treatment and improves its processability.

[0043] To further improve the efficiency of the curing reaction, preferably, the curing reaction is carried out under ultrasonic and / or stirring conditions.

[0044] To further improve the efficiency of the curing reaction, the ultrasonic power is preferably 100-300W; the stirring speed is preferably 110-140rpm / min.

[0045] Microgravure coating is a contact coating method. In a preferred embodiment, microgravure coating is used in step S3. This coating method facilitates improved processing efficiency and allows for easy control of the thickness of the first modified layer 21 and the second modified layer 22.

[0046] 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 corrosion resistance and tensile strength.

[0047] In a preferred embodiment, the weight ratio of chitosan, guar gum, ester-based protective agent, and coupling agent is (1–5):0.1:(1–5):(5–7.5). Compared to other ranges, limiting the weight ratio of chitosan, guar gum, ester-based protective agent, and coupling agent to the above range is beneficial to further exert their synergistic effect, thereby facilitating the improvement of the bonding force between the layers in the negative electrode composite current collector and the resistance to electrolyte corrosion, thus improving the service life of the negative electrode composite current collector.

[0048] 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.

[0049] 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, including but not limited to, 1 to 10 nm.

[0050] 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.

[0051] In a preferred embodiment, the thickness of the substrate layer 10 is 2–6.5 μm, more preferably 2.4–4.5 μm. The thickness of the substrate layer 10 includes, but is not limited to, the above range. Limiting it to the above range helps to reduce the weight of the negative electrode composite current collector and also helps to improve its flexibility.

[0052] 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 terephthalate, polyethylene terephthalate, and polycarbonate. All of the above materials belong to polyester materials, and the negative electrode composite material provided in this application is particularly suitable for the substrate layer 10 made of polyester material, thereby inhibiting the degradation of the polyester material after immersion in the electrolyte.

[0053] 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 reducing the thickness of the negative electrode composite current collector while increasing the energy density of the lithium-ion battery. It also helps reduce the risk of the first conductive layer 31 and the second conductive layer 32 detaching or peeling off, thereby extending the lifespan of the lithium-ion battery.

[0054] 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.

[0055] 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. Compared to other types, the first conductive layer 31 and the second conductive layer 32 described above are suitable for negative electrode composite current collectors, have better conductivity, and are less expensive.

[0056] The negative electrode composite current collector provided in this application has good adhesion between the layers, and the risk of the first conductive layer 31 and the second conductive layer 32 falling off or peeling is low. In a preferred embodiment, the dry bonding force between the substrate layer 10 and the first conductive layer 31 or the second conductive layer 32 is 5 to 10 N / 15 mm; the wet bonding force between the substrate layer 10 and the first conductive layer 31 or the second conductive layer 32 is 2 to 7 N / 15 mm.

[0057] The negative electrode composite current collector provided in this application has excellent tensile strength. In a preferred embodiment, the tensile strength of the negative electrode composite current collector in the MD direction (longitudinal direction) is ≥200MPa, and the tensile strength in the TD direction (transverse direction) is ≥170MPa.

[0058] 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.

[0059] 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 corrosion resistance.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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 provided in this application 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 in this application exhibits strong interlayer bonding and excellent resistance to electrolyte corrosion, demonstrating excellent structural stability. Applying the aforementioned negative electrode composite current collector to lithium-ion batteries can improve their electrochemical performance and lifespan.

[0066] 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.

[0067] Example 1

[0068] A method for preparing a negative electrode composite current collector, comprising:

[0069] (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.

[0070] (2) 5g of isopropyl di(methacryloyl)isostearoyl titanate, 3.9g of chitosan (weight average molecular weight of 15,000), and 0.1g of guar gum (weight average molecular weight of 200,000) were dissolved in 90g of DMF to obtain solution A. 1g of ester-protecting agent TMSE was added dropwise to solution A, and the mixture was subjected to ultrasonic and mechanical stirring. The ultrasonic power was 300W, and the mixture was stirred at 120rpm / min for 8 hours at 45℃ to obtain a mixed system. The solid content of this mixed system was 10wt%, and the viscosity was 150mPa·s.

[0071] (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 90°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.

[0072] (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;

[0073] (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.

[0074] The negative electrode composite current collector prepared in Example 1 has 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.

[0075] Example 2

[0076] The difference from Example 1 is that the weight percentage of chitosan in the mixed system is 1 wt%.

[0077] Example 3

[0078] The difference from Example 1 is that the weight percentage of chitosan in the mixed system is 5 wt%.

[0079] Example 4

[0080] The difference from Example 1 is that the weight percentage of chitosan in the mixed system is 0.5 wt%.

[0081] Example 5

[0082] The difference from Example 1 is that the weight percentage of TMSE in the mixture is 5 wt%.

[0083] Example 6

[0084] The difference from Example 1 is that the weight percentage of TMSE in the mixture is 6 wt%.

[0085] Example 7

[0086] The difference from Example 1 is that the curing reaction temperature is 50°C and the time is 10 minutes.

[0087] Example 8

[0088] The difference from Example 1 is that the curing reaction temperature is 100°C and the time is 1 minute.

[0089] Example 9

[0090] The difference from Example 1 is that the amount of isopropyl di(methacryloyl)isostearyl titanate was changed to make it account for 7.5 wt% of the weight of the mixture.

[0091] Example 10

[0092] The difference from Example 1 is that the amount of isopropyl di(methacryloyl)isostearyl titanate is changed so that it accounts for 10 wt% of the weight of the mixture.

[0093] Comparative Example 1

[0094] 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.

[0095] Comparative Example 2

[0096] 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.

[0097] 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 immersion in electrolyte at 45°C for 7 days, the tensile strength of the negative electrode composite current collector in the MD and TD directions was tested using a universal tensile testing machine. The peel strength of the first conductive layer 31 and the second conductive layer 32 was tested using the current collector peel strength testing method provided in Chinese Patent Application 202310804230.2, under both dry conditions and electrolyte immersion conditions (85°C, immersion for 3 days). The electrolyte used was a commercial electrolyte, model Hairong 9212. The test results are shown in Table 1. In Table 1, the negative electrode composite current collector prepared in Comparative Example 1 detached after immersion in electrolyte, and the peel strength value could not be measured.

[0098] 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 separator 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. The internal resistance, initial discharge capacity, and cycle stability were tested. The initial discharge capacity was tested using the coulombic efficiency method. 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.

[0099] Table 1

[0100]

[0101] Table 2

[0102]

[0103] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: Chitosan contains a large number of amino groups. After coating the mixed system containing amino groups onto both sides of the substrate layer 10 to form the first modified layer 21 and the second modified layer 22, it can bond with the materials (such as copper elements) in the first conductive layer 31 or the second conductive layer 32, thereby improving the bonding force between the substrate layer 10 and the first conductive layer 31 and the second conductive layer 32, and thus reducing the risk of peeling or detachment of the first conductive layer 31 and the second conductive layer 32, and improving the structural stability of the negative electrode composite current collector. At the same time, the ester-based protective agent in the mixed system contains silicone protective groups, which can effectively inhibit the acid or alkali hydrolysis of the ester groups in the polyester material, thereby protecting the ester-containing substrate layer 10 from being degraded by the electrolyte, and thus improving the corrosion resistance of the negative electrode composite current collector. Furthermore, the introduction of guar gum as a thickener into the mixing system, along with the combination of chitosan and ester-based protective agents, facilitates their synergistic effect, thereby improving the bonding strength between the layers in the negative electrode composite current collector and its resistance to electrolyte corrosion, thus extending the service life of the negative electrode composite current collector.

[0104] As shown in Table 2, the initial discharge capacity of the lithium-ion batteries containing the above-mentioned negative electrode composite current collector prepared in Examples 1 to 10 of this application is greater than that of Comparative Examples 1 and 2, indicating that the lithium-ion batteries obtained in each embodiment of this application have better discharge performance. The internal resistance of the lithium-ion batteries containing the above-mentioned negative electrode composite current collector prepared in Examples 1 to 10 of this application is significantly lower than that of Comparative Examples 1 and 2, indicating that the lithium-ion batteries obtained in each embodiment of this application have lower internal resistance. The number of cycles required for the lithium-ion batteries in Examples 1 to 10 of this application to reach 80% capacity at room temperature is greater than that of Comparative Examples 1 and 2, indicating that the lithium-ion batteries obtained in each embodiment of this application have better cycle performance.

[0105] 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.

[0106] 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) made of a polyester material; a first modified layer (21) disposed on one side surface of the substrate layer (10); a second modified layer (22) disposed on the other side surface of the substrate layer (10); a first conductive layer (31) disposed on the side surface of the first modified layer (21) away from the substrate layer (10); a second conductive layer (32) disposed on the other 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 chitosan, guar gum, an ester-based protective agent, a coupling agent, and 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 weight average molecular weight of the chitosan is 15000-20000; Preferably, the weight percentage content of the chitosan in the mixed system is 1-5wt%.

3. The negative electrode composite current collector according to claim 1 or 2, characterized in that, The weight average molecular weight of the guar gum is 200-300w; Preferably, the weight percentage content of the guar gum in the mixed system is 0.1-1wt%.

4. The negative composite current collector according to any one of claims 1 to 3, characterized in that, The weight percentage content of the ester-based protective agent in the mixed system is 1-5wt%; Preferably, the weight percentage content of the coupling agent in the mixed system is 5-7.5wt%; More preferably, the ester-based protective agent is selected from one or more of the group consisting of trimethylsilyl ethyl alcohol ester, triphenylmethyl diphenyl silane, and methoxy methyl ether; More preferably, the coupling agent is selected from one or more of the group consisting of titanium ester coupling agent, further preferably isopropyl di(methacryl) isostearoyl titanate, isopropyl tri(dioctyl phosphoric acyloxy) phthalate, and isopropyl di-oleic acyloxy(dioctyl phosphoric acyloxy) phthalate; More preferably, the solvent is selected from one or more of the group consisting of N,N-dimethyl formamide, dimethyl sulfoxide, and N-methyl pyrrolidone.

5. The negative composite current collector according to claim 4, wherein The solid content of the mixed system is 5-10wt%, and the viscosity is 100-200mPa·s; Preferably, the mixing in step S1 is carried out under ultrasonic and / or stirring conditions; preferably, the power of the ultrasonic is 100-300W; preferably, the stirring speed is 110-140rpm / min.

6. The negative composite current collector according to claim 5, wherein In step S3, the coating is carried out by micro-concave coating method; and / or, the temperature of the curing reaction is 50-100℃, and the time is 1-10min.

7. The negative composite current collector of claim 1, wherein The weight ratio of the chitosan, the guar gum, the ester-based protective agent, and the coupling agent is (1-5):0.1:(1-5):(5-7.5).

8. The negative composite current collector according to any one of claims 1 to 7, 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 1-10 nm; Preferably, the first metal oxide layer (41) and the second metal oxide layer (42) are independently selected from a copper oxide layer; Preferably, the thickness of the substrate layer (10) is 2-6.5 μm, more preferably 2.4-4.5 μm; Preferably, the material of the substrate layer (10) is selected from one or more of the group consisting of polyethylene terephthalate, polyethylene terephthalate and polycarbonate; Preferably, the thickness of the first modified layer (21) and the second modified layer (22) is independently selected from 0.2-1 μm; Preferably, the thickness of the first conductive layer (31) and the second conductive layer (32) is independently selected from 0.1-1.51 μm; Preferably, the first conductive layer (31) and the second conductive layer (32) are independently selected from a copper layer; Preferably, the dry adhesion between the substrate layer (10) and the first conductive layer (31) or the second conductive layer (32) is 5-10 N / 15 mm; Preferably, the wet adhesion between the substrate layer (10) and the first conductive layer (31) or the second conductive layer (32) is 2-7 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 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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