Preparation method of composite current collector

Abstract

The invention specifically discloses a preparation method of a composite current collector. The preparation method of the composite current collector comprises the following steps: S1, preparing a seed layer on the surface of a macromolecular base membrane to obtain a pretreated base membrane; and S2, performing molten salt electroplating on the pretreated base film to generate a metal layer, thereby obtaining the composite current collector, wherein an inorganic molten salt system used in the molten salt electroplating process is obtained by mixing metal salts including AlCl3, NaCl, KCl and CaCl2; in the process of forming the metal layer, the current density in the molten salt electroplating process is 0 mA. Cm <-2 >-50 mA. Cm <-2 >, and the electroplating temperature in the molten salt electroplating process is 110-180 DEG C. The composite current collector has the advantages that the pinhole defect in the composite current collector is reduced, and the conductivity and mechanical strength of the composite current collector are improved.

Description

Technical Field

[0001] The present application relates to the technical field of current collectors, and in particular to a method for preparing a composite current collector. Background Art

[0002] With the rapid development of new energy and advanced manufacturing, key battery performance indicators such as cycle life, safety, and energy density urgently need to be improved. The current collector is a key component in the battery, serving to collect current. Its performance directly impacts the battery's cycle life, energy density, safety, and other technical indicators.

[0003] At present, the common current collectors in the battery industry are mostly made of copper foil and aluminum foil. Current collectors made of pure metal have high cost and quality, and their performance in battery safety is often unsatisfactory. In addition, pure metal current collectors also have high "dead weight", which is not conducive to improving the energy density of the battery. The traditional composite aluminum foil production process is generally obtained by evaporating aluminum vapor onto polymer materials under a vacuum environment. However, since the aluminum vapor temperature in this process can often reach thousands of degrees Celsius, the plating process may cause polymer film ablation, and the process window is small. It often requires multiple evaporation processes to obtain a film layer with good performance. In addition, since the precipitation potential of aluminum is lower than the hydrogen production potential, the electroplating method in aqueous solution is not suitable for processing aluminum current collectors. Therefore, it is necessary to develop a new current collector preparation method to reduce production defects and improve the process window. Summary of the Invention

[0004] In order to solve the problems in the prior art, the present application provides a method for preparing a composite current collector.

[0005] The present application provides a method for preparing a composite current collector, which adopts the following technical solution: A method for preparing a composite current collector comprises the following steps: S1, preparing a seed layer on the surface of the polymer base film to obtain a pretreated base film; S2, performing molten salt electroplating on the pretreated base film to form a metal layer to obtain the composite current collector; The inorganic molten salt system used in the molten salt electroplating process is obtained by mixing metal salts including AlCl3, NaCl, KCl, and CaCl2; in the process of forming the metal layer, the current density in the molten salt electroplating process is 0mA.cm -2 -50mA.cm -2 , the electroplating temperature in the molten salt electroplating process is 110-180℃.

[0006] In the present application, a metal layer is generated on the surface of the seed layer by a molten salt electroplating method. First, molten salt electroplating will not produce hydrogen evolution as in aqueous solution electroplating, thereby avoiding the appearance of a large number of holes and gaps in the metal layer caused by hydrogen evolution, which helps to improve the electrical and mechanical properties of the metal layer. Second, the electroplating temperature in the molten salt electroplating process adopted in the present application is low, which not only does not have a negative impact on the stability of the polymer base film, but also does not require multiple evaporation processes like steam evaporation to obtain a metal layer. By adjusting the appropriate current density and electroplating temperature, the present application can form a metal layer on the surface of the seed layer in one step, which helps to improve the surface quality and flatness of the metal layer, and has high process stability, which helps to further improve the conductivity and mechanical strength of the composite current collector. Third, by selecting a suitable inorganic molten salt system and controlling the current density, the present application can achieve control of the crystal phase and morphology in the metal layer, which helps to improve the uniformity of the grains in the metal layer, thereby improving the uniformity of the current distribution in the composite current collector, and will not cause local overheating of the composite current collector, which can improve the cycle stability and service life of the lithium battery.

[0007] Preferably, in S1, the seed layer is prepared on the surface of the polymer base film by magnetron sputtering.

[0008] Preferably, the sputtering power during the magnetron sputtering process is 6-12 kW, and the background vacuum is 3×10 -3 -5×10 -3 Pa, argon flow rate is 80-130sccm, the cooling temperature of the sputtering main roller is -35 to 0°C, the aluminum target power is 8-12kW, and the winding speed is 5-8m / min.

[0009] Preferably, the mass ratio of AlCl3, NaCl, KCl and CaCl2 is (74-86): (7-11): (7-11): (0-4).

[0010] By adjusting the metal salt composition in the inorganic molten salt system, the present application can appropriately adjust the electroplating temperature of the inorganic molten salt system during the electroplating process to maintain it at a low level, so that the molten salt electroplating treatment can be applied to different types of polymer base films, such as PET, PP, PI, etc., thereby broadening the scope of application of the molten salt electroplating in this application.

[0011] Preferably, the current density during the molten salt electroplating process is from 0 to 5 mA.cm -2 Gradually increase to 45-50mA.cm -2 .

[0012] Preferably, during the molten salt electroplating process, the pretreated base film sequentially passes through multiple stages of different current densities, so that the difference between the current density of the latter stage and the current density of the previous stage always satisfies 0-10mA.cm -2 .

[0013] As the molten salt electroplating process proceeds, the total thickness of the composite current collector gradually increases. By timely adjusting the current density during the electroplating process to gradually increase, it helps to improve the deposition uniformity of the metal layer, form a metal layer with stable performance and stable bonding with the seed layer, and improve the surface flatness of the metal layer, avoiding pinhole defects in the metal layer, while improving the conductivity and mechanical strength of the composite current collector while ensuring a high yield in the production process.

[0014] Preferably, after preparing the seed layer on the surface of the polymer base film, an alloy layer is further deposited to obtain the pretreated base film; the thickness of the alloy layer is 10-30nm; the material of the alloy layer includes at least one of copper, nickel, zinc and titanium.

[0015] By depositing an alloy layer on the surface of the seed layer, the low-thickness alloy layer can not only prevent oxidation on the surface of the obtained pre-treated base film aluminum layer, but also improve the conductivity of the pre-treated base film, and can further improve the density of the subsequent electroplated metal aluminum layer and reduce the number of holes.

[0016] Preferably, the mass ratio of copper, nickel, zinc and titanium in the alloy layer is (60-80):(10-20):(5-10):(5-10).

[0017] By adjusting the mass ratio of copper, nickel, zinc and titanium in the alloy layer, the conductivity of the pre-treated base film and the density of the subsequent electroplated metal aluminum layer can be further improved; in addition, it can not only improve the corrosion resistance and wear resistance of the composite current collector, but also effectively solve the problem of adhesion between the membranes when the pre-treated base film is rolled up, further reducing the number of holes.

[0018] Preferably, metal salts including NaCl, KCl, and CaCl2 are mixed and dried, cooled and then mixed with AlCl3, and then electrolytically removed to obtain the inorganic molten salt system.

[0019] Preferably, the mixture is cooled to below 250°C and then mixed with AlCl3; the drying temperature is 300°C and the drying time is 2h.

[0020] Preferably, the current density of the electrolytic dedoping is 5-10 mA.cm 2 , the electrolysis time is 3-5h.

[0021] By electrolytically de-doping the inorganic molten salt system, the influence of impurity ions on the subsequent metal layer deposition process can be removed at this current density, thereby improving the integrity and purity of the metal layer; the electrical conductivity of the composite current collector and its ability to resist electrolyte corrosion can be significantly improved, and the metal layer has high mechanical strength, which can better withstand the residual stress generated by the battery during the charging and discharging process, thereby helping to improve the overall performance of the composite current collector.

[0022] Preferably, the thickness of the seed layer is 50-100 nm; the thickness of the metal layer is 1-3 μm. DETAILED DESCRIPTION

[0023] For better understanding and implementation, the technical solution of the present application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0025] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that can vary depending upon the desired properties sought to be obtained.

[0026] As used herein, "and / or" means one or all of the mentioned elements.

[0027] As used herein, “including” and “comprising” encompasses the case where only the stated elements are present and also the case where there are other elements other than the stated elements.

[0028] All percentages in this application are by weight unless otherwise stated.

[0029] Unless otherwise indicated, as used in this specification, "a," "an," "an," and "the" are intended to include "at least one" or "one or more." For example, "a component" refers to one or more components, and thus more than one component is contemplated and may be employed or used in the practice of the described embodiment.

[0030] The metal salts used in this application were of analytical grade.

[0031] Example 1 A method for preparing a composite current collector comprises the following steps: S1, after the sputtering chamber is vacuumed, start sputtering to treat the surface of the polymer base film (commercial PI film, thickness of 4.5μm) by magnetron sputtering (the parameters during magnetron sputtering are set as follows: the background vacuum degree is 5×10 -3Pa, argon flow rate of 130sccm, sputtering main roller cooling temperature of -25℃, aluminum target (target material purity of 99.99%) power of 10kW, winding speed of 7m / min), a seed layer with a thickness of 50nm was formed on the surface of the polymer base film to obtain a pretreated base film; S2, NaCl, KCl, CaCl2 were mixed and dried at 300℃ for 2h, and then mixed with AlCl3 (AlCl 3、 The mass ratio of NaCl, KCl, and CaCl2 is 80:9:9:2), and then the current density is 5 mA.cm 2 Electrolysis was performed for 180 min to remove impurities and obtain an inorganic molten salt system; Heat the inorganic molten salt system to 150°C to obtain molten salt, place the pretreated base film in the molten salt, and control the current density to 3 mA.cm -2 、8mA.cm -2 、13mA.cm -2 、18mA.cm -2 、23mA.cm -2 、28mA.cm -2 、33mA.cm -2 、38mA.cm -2 、43mA.cm -2 、48mA.cm -2 , a metal aluminum layer with a thickness of 100 nm for each sublayer and a thickness of 1 μm on one side is obtained, that is, a composite current collector is obtained.

[0032] Example 2 A method for preparing a composite current collector comprises the following steps: S1, after the sputtering chamber is vacuumed, start sputtering to treat the surface of the polymer base film (commercial PET film, thickness of 4.5μm) by magnetron sputtering (the parameters during magnetron sputtering are set as follows: the background vacuum degree is 5×10 -3 Pa, argon flow rate of 130sccm, sputtering main roller cooling temperature of -5°C, aluminum target (target material purity of 99.99%) power of 8kW, winding speed of 5m / min), a seed layer with a thickness of 70nm was formed on the surface of the polymer base film to obtain a pretreated base film; S2, NaCl, KCl, CaCl2 were mixed and dried at 300℃ for 2h, and then mixed with AlCl3 (AlCl 3、 The mass ratio of NaCl, KCl, and CaCl2 is 80:9:9:2), and then the current density is 5 mA.cm 2 Electrolysis was performed for 180 min to remove impurities and obtain an inorganic molten salt system; The inorganic molten salt system is heated to 150°C to obtain molten salt, the pretreated base film is placed in the molten salt, and the current density is controlled from 2 mA.cm -2 、6mA.cm -2 、12mA.cm -2 、18mA.cm -2 , 22mA.cm -2 、26mA.cm -2 、30mA.cm -2 、36mA.cm -2 、44mA.cm -2 、50mA.cm -2 , obtaining a sub-layer thickness of 100 nm, and obtaining a metal aluminum layer with a thickness of 1 μm on one side, thereby obtaining a composite current collector.

[0033] Example 3 A method for preparing a composite current collector comprises the following steps: S1, after the sputtering chamber is vacuumed, start sputtering to treat the surface of the polymer base film (commercial PP film, thickness of 4.5μm) by magnetron sputtering. (The parameters during magnetron sputtering are set as follows: the background vacuum degree is 5×10 -3 Pa, argon flow rate of 130sccm, sputtering main roller cooling temperature of -30℃, aluminum target (target material purity of 99.99%) power of 12kW, winding speed of 8m / min), a seed layer with a thickness of 100nm was generated on the surface of the polymer base film to obtain a pretreated base film; S2, NaCl, KCl, CaCl2 were mixed and dried at 300℃ for 2h, and then mixed with AlCl3 (AlCl 3、 The mass ratio of NaCl, KCl, and CaCl2 is 80:9:9:2), and then the current density is 5 mA.cm 2 Electrolysis was performed for 180 min to remove impurities and obtain an inorganic molten salt system; The inorganic molten salt system is heated to 150°C to obtain molten salt, the pretreated base film is placed in the molten salt, and the current density is controlled from 4 mA.cm -2 , 9mA.cm -2 、14mA.cm -2 、18mA.cm -2 、23mA.cm -2 、29mA.cm -2 、33mA.cm -2 、36mA.cm -2 、45mA.cm -2 、50mA.cm -2, obtaining a sub-layer thickness of 100 nm, and obtaining a metal aluminum layer with a thickness of 1 μm on one side, thereby obtaining a composite current collector.

[0034] Example 4 The difference between this embodiment and Example 1 is that the mass ratio of the metal salts AlCl3, NaCl, KCl, and CaCl2 used in the molten salt electroplating process is 70:12:12:6; the other steps and parameter settings are consistent with Example 1.

[0035] Example 5 The difference between this embodiment and Example 1 is that the mass ratio of the metal salts AlCl3, NaCl, KCl, and CaCl2 used in the molten salt electroplating process is 85:6:6:3; the other steps and parameter settings are consistent with Example 1.

[0036] Example 6 The difference between this embodiment and embodiment 1 is that after the pre-treated base film in S2 is placed in the molten salt, the current density is increased from 5 mA.cm -2 、10mA.cm -2 、16mA.cm -2 、16mA.cm -2 , 20mA.cm -2 , 20mA.cm -2 , 20mA.cm -2 、30mA.cm -2 、42mA.cm -2 、50mA.cm -2 ; Other steps and parameter settings are consistent with Example 1.

[0037] Example 7 The difference between this embodiment and embodiment 1 is that after the pre-treated base film in S2 is placed in the molten salt, the current density is increased from 4 mA.cm -2 , 20mA.cm -2 、26mA.cm -2 、35mA.cm -2 、48mA.cm -2 、50mA.cm -2 ; Other steps and parameter settings are consistent with Example 1.

[0038] Example 8 The difference between this embodiment and embodiment 1 is that, in the metal salt mixing step, NaCl, KCl, CaCl2, and AlCl3 are mixed simultaneously and then dried; the other steps and parameter settings are consistent with those in embodiment 1.

[0039] Example 9 The difference between this embodiment and embodiment 1 is that, after a seed layer with a thickness of 50 nm is formed on the surface of the polymer base film in S1, an alloy layer is deposited to obtain a pretreated base film; In the process of depositing the alloy layer by magnetron sputtering, the target material used includes copper, nickel, zinc, and titanium in a mass ratio of 50:20:20:10. The thickness of the alloy layer is 10 nm, and the materials in the alloy layer include copper, nickel, zinc, and titanium in a mass ratio of 50:20:20:10; the other steps and parameter settings are consistent with Example 1.

[0040] Example 10 The difference between this embodiment and embodiment 9 is that, in the process of depositing the alloy layer by magnetron sputtering, the target material used is copper, nickel, zinc, and titanium with a mass ratio of 60:20:10:10; the other steps and parameter settings are consistent with embodiment 1.

[0041] Example 11 The difference between this embodiment and Example 9 is that, in the process of depositing the alloy layer by magnetron sputtering, the target material used is copper, nickel, zinc, and titanium with a mass ratio of 70:10:10:10; the other steps and parameter settings are consistent with Example 1.

[0042] Example 12 The difference between this embodiment and embodiment 9 is that, in the process of depositing the alloy layer by magnetron sputtering, the target material used is copper, nickel, zinc, and titanium with a mass ratio of 80:10:5:5; the other steps and parameter settings are consistent with embodiment 1.

[0043] Example 13 The difference between this embodiment and embodiment 9 is that, in the process of depositing the alloy layer by magnetron sputtering, the target material used is copper, nickel, zinc, and titanium with a mass ratio of 90:5:2:3; the other steps and parameter settings are consistent with embodiment 1.

[0044] Example 14 The difference between this embodiment and embodiment 11 is that the thickness of the alloy layer is 20 nm; other steps and parameter settings are consistent with embodiment 1.

[0045] Example 15 The difference between this embodiment and embodiment 11 is that the thickness of the alloy layer is 30 nm; other steps and parameter settings are consistent with embodiment 1.

[0046] Example 16 The difference between this embodiment and embodiment 11 is that the thickness of the alloy layer is 40 nm; other steps and parameter settings are consistent with embodiment 1.

[0047] Example 17 The difference between this embodiment and embodiment 11 is that the thickness of the alloy layer is 5 nm; other steps and parameter settings are consistent with embodiment 1.

[0048] Comparative Example 1 The difference between this comparative example and Example 1 is that in S2, magnetron sputtering is still used to treat the pretreated base film to generate a metal aluminum layer to obtain a composite current collector; other steps and parameter settings are consistent with Example 1.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is that the metal aluminum layer is plated on the surface of the polymer base film by vacuum evaporation, and the entire plating process is carried out by the evaporation method.

[0050] Comparative Example 3 The difference between this comparative example and Example 1 is that the current density during the molten salt electroplating process is always 60 mA.cm -2 ; Other steps and parameter settings are consistent with Example 1.

[0051] Test Method 1. Test of the number of pinholes in the composite current collector The composite current collectors in the above embodiments and comparative examples were tested for the number of pinholes. The length of the composite current collector was 3000 m and the width was 1.35 m. The composite current collector was detected using a CCD device. The number of pinholes with test apertures of 50-100 μm, 100-200 μm, 200-300 μm, and 300-500 μm was measured, and the test data was recorded in Table 1.

[0052] 2. Composite current collector square resistance test The composite current collectors in the above embodiments and comparative examples were subjected to a square resistance test. The square resistance of the current collectors was measured in accordance with the provisions of GB / T 15717-2021 "Test method for thickness of vacuum metal coatings - resistance method", and the test data were recorded in Table 1.

[0053] 3. Composite current collector tensile strength test The composite current collectors in the above embodiments and comparative examples were subjected to a tensile strength test. The test method was as follows: three samples were taken using a special test die, the samples were placed between the test fixtures and fixed, and the universal tensile testing machine was controlled by a computer to stretch the fixtures outward until the samples broke. The readings were recorded in Table 1.

[0054] Table 1

[0055] In combination with Examples 1-3, Comparative Examples 1-3 and Table 1, it can be seen that the present application can significantly reduce the number of holes and gaps on the surface of the composite current collector by preparing a seed layer on the surface of the polymer base film and generating a metal aluminum layer on the surface of the seed layer by molten salt electroplating. In addition, due to the high uniformity of the grains formed in the metal aluminum layer and the high surface quality and flatness of the metal aluminum layer formed by one-time molding in the present application, it helps to significantly improve the tensile strength of the composite current collector. Therefore, the number of pinholes in the composite current collector prepared by the method of the present application is significantly increased when the number of pinholes is reduced compared to that in Comparative Example 1.

[0056] In combination with Example 1, Examples 4-5 and Table 1, it can be seen that when the proportion of metal salt in the inorganic molten salt system used in the molten salt electroplating process does not meet the limit, the number of pinholes in the composite current collector increases significantly, the tensile strength decreases and the square resistance increases, especially when the mass proportion of aluminum salt in the metal salt is low (Example 4), this change is more significant. Therefore, in the molten salt electroplating process, an aluminum salt with an appropriate mass proportion should be selected for operation.

[0057] In combination with Example 1, Examples 6-7 and Table 1, it can be seen that when the current density in the molten salt electroplating process does not meet the limit, the number of pinholes in the composite current collector increases significantly and the tensile strength decreases. This is because the metal aluminum layer deposited under the above-mentioned current density control has poor uniformity and poor bonding stability with the seed layer, and the surface flatness of the metal aluminum layer itself is also low, and vacuum defects are prone to occur, which have a negative impact on the performance of the composite current collector.

[0058] In combination with Example 1, Example 8 and Table 1, it can be seen that when the metal salts AlCl3, NaCl, KCl, and CaCl2 are mixed and dried at the same time, the number of pinholes in the composite current collector increases significantly and the tensile strength decreases. This may be because aluminum chloride will decompose to a certain extent at the drying temperature during the drying process, which is not conducive to the formation of a metal aluminum layer with a small number of defects on the surface of the seed layer during the subsequent molten salt electroplating process.

[0059] In combination with Example 1, Examples 10-13, 14-15 and Table 1, it can be seen that when the pretreated base film includes a seed layer and an alloy layer, the number of pinholes in the composite current collector is significantly reduced and the tensile strength is improved. This is because the alloy layer can not only prevent oxidation of the surface of the aluminum layer of the pretreated base film, but also improve the conductivity of the pretreated base film, thereby further improving the density of the subsequent electroplated metal aluminum layer and improving the tensile strength of the composite current collector.

[0060] Combining Examples 9-13 and Table 1, it can be seen that when the mass ratio in the alloy layer does not meet the specified range, the number of pinholes in the composite current collector in Examples 9 and 13 is significantly increased compared with Example 11. This is because the conductivity of the alloy layer at this time is poor, which is not conducive to improving the density of the metal aluminum layer formed by subsequent molten salt electroplating.

[0061] Combining Examples 11, 14-17 and Table 1, it can be seen that although the tensile strength of the composite current collector is slightly improved with the increase in the thickness of the alloy layer, the number of holes in the composite current collector at this time shows an increasing trend compared with Example 11.

[0062] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the technical solutions of the present application can be modified or replaced by equivalents, but these modifications or replacements are all within the scope of protection of the present application.

Claims

1. A method for preparing a composite current collector, characterized in that: The steps include: S1, preparing a seed layer on the surface of the polymer base film to obtain a pretreated base film; S2, performing molten salt electroplating on the pretreated base film to form a metal layer to obtain the composite current collector; The inorganic molten salt system used in the molten salt electroplating process is obtained by mixing metal salts including AlCl3, NaCl, KCl, and CaCl2; in the process of forming the metal layer, the current density in the molten salt electroplating process is 0mA.cm -2 -50mA.cm -2 , the electroplating temperature in the molten salt electroplating process is 110-180℃.

2. The method for preparing a composite current collector according to claim 1, wherein: The mass ratio of AlCl3, NaCl, KCl and CaCl2 is (74-86):(7-11):(7-11):(0-4).

3. The method for preparing a composite current collector according to claim 1, wherein: The current density during molten salt electroplating ranges from 0 to 5 mA.cm -2 Gradually increase to 45-50mA.cm -2 .

4. The method for preparing a composite current collector according to claim 3, wherein: During the molten salt electroplating process, the pretreated base film is sequentially subjected to multiple stages of different current densities, so that the difference between the current density of the latter stage and the current density of the previous stage always satisfies 0-10mA.cm -2 .

5. The method for preparing a composite current collector according to claim 1, wherein: After preparing the seed layer on the surface of the polymer base film, an alloy layer is continuously deposited to obtain the pretreated base film; The thickness of the alloy layer is 10-30 nm; The material of the alloy layer includes at least one of copper, nickel, zinc and titanium.

6. The method for preparing a composite current collector according to claim 5, wherein: The mass ratio of copper, nickel, zinc and titanium in the alloy layer is (60-80):(10-20):(5-10):(5-10).

7. The method for preparing a composite current collector according to claim 1, wherein: The inorganic molten salt system is obtained by mixing metal salts including NaCl, KCl and CaCl2, drying the mixture, cooling the mixture and then mixing the mixture with AlCl3, and performing electrolytic dedoping. The current density of electrolytic desorption is 5-10 mA.cm 2 , the electrolysis time is 3-5h.

8. The method for preparing a composite current collector according to any one of claims 1 to 7, wherein: The thickness of the seed layer is 50-100 nm; the thickness of the metal layer is 1-3 μm.

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