High-conductivity current collector for secondary battery and preparation method of high-conductivity current collector

Abstract

The invention relates to the technical field of current collectors for secondary batteries, and particularly discloses a high-conductivity current collector for a secondary battery and a preparation method of the high-conductivity current collector. The high-conductivity current collector for the secondary battery comprises a current collector body and a functional coating arranged on the surface of the current collector body, and the functional coating is prepared from the following raw materials in parts by weight: 3-6 parts of a conductive agent; 3-6 parts of a dispersant; 3-8 parts of a binder; 80 to 90 parts of a solvent; 0.5 to 3 parts of polyethylene glycol; 3-6 parts of cocoanut fatty acid diethanolamide; and 0.1 to 0.5 part of sodium fluosilicate. When the obtained high-conductivity current collector for the secondary battery bears frequent temperature changes, a large molecular motion gap is not prone to being formed in the functional coating, the high-conductivity current collector still can keep good bonding stability and conductive stability, the overall high-conductivity current collector has remarkable and excellent application stability, meanwhile, the preparation process is simple in technology, and the production cost is low. And the production efficiency is high.

Description

Technical Field

[0001] The present application relates to the technical field of current collectors for secondary batteries, and more specifically, to a highly conductive current collector for secondary batteries and a preparation method thereof. Background Art

[0002] Among secondary batteries, lithium batteries are the most representative. Due to their excellent comprehensive performance such as high specific energy, long cycle life and high output voltage, they are widely used in 3C consumer fields, energy storage and automotive power, and occupy an important position in the market.

[0003] Among the main materials used in the manufacturing of secondary batteries such as lithium batteries and sodium batteries, the current collector occupies an important position among the positive and negative electrode materials. As a structure or component for collecting current, its function is to carry the active substances of the positive and negative electrodes, and to collect the currents generated by the chemical reactions of the active substances to form a larger current for external output, thereby completing the conversion process of chemical energy into electrical energy. The internal resistance should be as small as possible to optimize performance and improve the output power and efficiency of the battery.

[0004] In the prior art, surface treatment of battery substrates by functionalized coating is a breakthrough work of technological innovation. For example, the invention patent application with publication number CN104319364A discloses a positive electrode sheet for reducing the DC internal resistance of a battery and a preparation method thereof. The positive electrode sheet is composed of an aluminum foil and a single graphene coating and a nano-carbon fiber slurry coating alternately arranged on any one or both sides of the aluminum foil. The single graphene coating is formed by coating a single graphene slurry, and the nano-carbon fiber slurry coating is formed by a nano-carbon fiber slurry. The nano-carbon fiber slurry is a slurry formed by an active substance, a binder, a solvent, and nano-carbon fibers.

[0005] With respect to the above-mentioned related technologies, the inventors believe that when heat is generated inside the battery, the current collector itself will inevitably be subjected to frequent temperature changes in order to effectively disperse and conduct the heat. The increase in temperature will reduce the density of the fluid because the increase in molecular thermal motion leads to an increase in the gaps between molecules, which will not only lead to a significant decrease in the bonding stability of the functionalized coating, but also affect its surface resistance, resulting in a loss of conductive properties.

[0006] Therefore, it is urgent to propose a solution to solve the above technical problems. Summary of the invention

[0007] In order to improve the adhesion performance and the stability of the conductive performance of the surface functionalized coating of the current collector during its application, the present application provides a highly conductive current collector for a secondary battery and a preparation method thereof.

[0008] In a first aspect, the present application provides a highly conductive current collector for a secondary battery, which adopts the following technical solution: a highly conductive current collector for a secondary battery, comprising a current collector body and a functional coating disposed on the surface of the current collector body, wherein the functional coating is made of raw materials comprising the following parts by weight: Conductive agent 3-6 parts; 3-6 parts of dispersant; 3-8 parts of binder; 80-90 parts of solvent; 0.5-3 parts of polyethylene glycol; Coconut oil fatty acid diethanolamide 3-6 parts; Sodium fluorosilicate 0.1-0.5 parts.

[0009] By adopting the above technical scheme, the combination of conductive agent, dispersant, adhesive and solvent can form a multi-dimensional conductive network after being evenly coated on the surface of the current collector, and form a strong connection structure with low surface resistance, thereby showing excellent high conductivity. Polyethylene glycol can effectively dissolve and disperse various raw materials, and enable them to better adhere to the substrate, thereby improving the bonding strength; coconut oil fatty acid diethanolamide can reduce the surface tension of the liquid, making it easier for the raw material mixture to penetrate into the tiny gaps of the material, thereby improving the strength and durability of the bonding; at the same time, when polyethylene glycol and coconut oil fatty acid diethanolamide are used in combination, their mutual surrounding and wrapping effect can form a stable suspension system, thereby improving the stability of the space and structure. Furthermore, sodium fluorosilicate can provide good adhesion and durability, and excels in high temperature resistance. When sodium fluorosilicate is applied to a suspension system constructed with polyethylene glycol and coconut oil fatty acid diethanolamide, it can exert a supporting effect, allowing the three to form a unique spatial stability system. When the highly conductive current collector for secondary batteries is subjected to frequent temperature changes, it is not easy for large molecular motion gaps to form inside the functional coating, and it can still maintain good adhesion stability and conductive stability, so that the highly conductive current collector for secondary batteries has significantly excellent application stability.

[0010] Preferably, the current collector body is one of aluminum foil, copper foil, carbon-coated aluminum foil and carbon-coated composite foil.

[0011] By adopting the above technical scheme, aluminum foil, copper foil, carbon-coated aluminum foil and carbon-coated composite foil can not only reduce the resistance of the current collector when transmitting current, improve the efficiency of the battery during operation, but also increase the output power and stability of the battery. They are all suitable for combination with functional coatings, thereby obtaining a highly conductive current collector for secondary batteries with excellent application quality.

[0012] Preferably, the conductive agent is a combination of any two or more of conductive carbon black, conductive graphite, graphene, carbon fiber and carbon nanotubes.

[0013] By adopting the above technical scheme, the above types of conductive agents can improve the electronic conductivity, reduce the contact resistance of the electrode, accelerate the electron movement rate, improve the charging and discharging efficiency of the battery, improve the electrode processability, and promote the infiltration of the electrolyte into the electrode, thereby increasing the service life of the battery; and selecting at least two of the above conductive agents for combination can more easily form a multi-dimensional conductive network, thereby exerting a more excellent application effect.

[0014] Preferably, the conductive agent is a composition of conductive carbon black and graphene, and the particle size D50 is 1-30 μm.

[0015] By adopting the above technical solution and selecting conductive carbon black and graphene for use in combination, not only can excellent conductive performance be achieved, but also a lower thermal effect can be achieved, effectively regulating the heat transfer of the battery. At the same time, a continuous barrier layer can be formed, which prolongs the transmission path of corrosive media such as water and air, slows down the surface corrosion of the electrode, and enhances the service life of the battery, thereby making the obtained high conductive current collector for secondary batteries have a better overall application effect.

[0016] Preferably, the binder is one or a combination of acrylic acrylonitrile resin, waterborne polyurethane, polytetrafluoroethylene, waterborne epoxy resin and waterborne alkyd resin.

[0017] By adopting the above technical solution, the above types of adhesives can form a stable and uniform dispersion system with other raw materials in the functional coating, and can firmly fix other raw materials in the functional coating on the current collector body, showing good bonding and adhesion.

[0018] Preferably, the binder is acrylic acrylonitrile resin, and the viscosity of the acrylic acrylonitrile resin at room temperature is not higher than 3000 mPa·s.

[0019] By adopting the above technical scheme, the high content of -COOH in the side chain of acrylic acrylonitrile resin is combined with the mechanical support capacity of CMC to have a synergistic effect, which can improve the adhesion between the functional coating and the current collector body, and at the same time enhance the mechanical strength of the current collector; and the viscosity is not higher than 3000mPa·s, which is not only easy to be evenly dispersed and mixed with other raw materials in the functional coating, but also can maintain moderate fluidity after mixing with other raw materials in the functional coating, which is more conducive to uniform coating on the current collector body and obtains an excellent functional coating structure.

[0020] Preferably, the solvent is one or a combination of deionized water, ethanol, isopropanol and n-butanol.

[0021] By adopting the above technical scheme, the above types of solvents are all suitable for the preparation of functional coatings. After being mixed and coated with other raw materials in the functional coating, a functional coating with excellent and stable structure can be obtained during the drying and curing process, and a stable bond can be formed with the current collector body.

[0022] Preferably, the thickness of the current collector is 5-30 μm, and the surface density of the functional coating is not more than 0.7 g / m 2 .

[0023] By adopting the above technical solution, when the thickness of the current collector is thin, the current density is very high, which will cause the electrochemical reaction rate to become very fast, easily produce excessive intermediate products, and aggravate electrode corrosion; when the current collector is thick, it will increase the internal resistance of the battery and limit the charging and discharging speed of the battery; and the current collector body of the above thickness can meet the application requirements and obtain a high-conductivity current collector for secondary batteries with excellent application quality. At the same time, the surface density of the functional coating is not more than 0.7g / m 2 It can not only obtain a stable and better bonding effect, but also reduce its own surface resistance, thereby showing excellent high conductivity.

[0024] In a second aspect, the present application provides a method for preparing a highly conductive current collector for a secondary battery, using the following technical solution: A method for preparing a highly conductive current collector for a secondary battery comprises the following steps: (1) preparing raw materials including a conductive agent, a dispersant, a binder, a solvent, polyethylene glycol, coconut oil fatty acid diethanolamide and sodium fluorosilicate according to a ratio; (2) after mixing the binder and part of the solvent in step (1), a conductive agent, a dispersant, polyethylene glycol, coconut oil fatty acid diethanolamide, sodium fluorosilicate and the remaining solvent are added and mixed to obtain a conductive paste; (3) The conductive slurry is coated on the surface of the current collector body and dried to form a functional coating to obtain a highly conductive current collector for a secondary battery.

[0025] By adopting the above technical scheme, in the preparation process of the conductive paste, polyethylene glycol, coconut oil fatty acid diethanolamide and sodium fluorosilicate are more easily fully matched and play a role, and the conductive paste is applied to the surface of the current collector body for drying and forming, so that a functional coating with excellent bonding stability can be obtained, and then a high-conductivity current collector for secondary batteries of excellent quality can be obtained. The overall preparation operation is simple, the production efficiency is high, and it is suitable for large-scale industrial production. At the same time, the conductive paste is an aqueous conductive paste, and when the pH at room temperature is 5 to 7 and the viscosity is 10 to 200 mPa·s, the application effect is better and the functional coating formed is better.

[0026] In summary, this application has the following beneficial effects: The present application uses polyethylene glycol, coconut oil fatty acid diethanolamide and sodium fluorosilicate in the preparation of the functional coating. The polyethylene glycol and coconut oil fatty acid diethanolamide are wrapped around the mixed system and combined with sodium fluorosilicate to form a unique spatial stabilization system. When the highly conductive current collector for the secondary battery is subjected to frequent temperature changes, it is not easy to form large molecular motion gaps inside the functional coating. It can still maintain good adhesion stability and conductive stability, and has significantly excellent application stability as a whole. DETAILED DESCRIPTION

[0027] The present application is further described in detail below in conjunction with embodiments and comparative examples.

[0028] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present application are commercially available: The polyethylene glycol used is commercially available as PEG-600; The coconut oil fatty acid diethanolamide used has a commercial purity of 98% and a CAS number of 68603-42-9; The acrylic acid acrylonitrile resin used has a commercial molecular weight of less than 300,000, a solid content of 25%, and a pH of 4 to 6; The waterborne epoxy resin used has a commercially available solid content of 50% and an epoxy equivalent of 450; The surface dyne values ​​of the aluminum foil and carbon-coated aluminum foil used are 28 to 35 dyn / cm, and the carbon-coated aluminum foil is carbon-coated on both sides with a thickness of 1 μm. Example

[0029] Example 1 A highly conductive current collector for a secondary battery comprises a current collector body and a functional coating disposed on the surface of the current collector body. The weight of the raw materials used to prepare the functional coating is shown in Table 1. The highly conductive current collector for a secondary battery is prepared by the following method: (1) preparing raw materials including a conductive agent, a dispersant, a binder, a solvent, polyethylene glycol, coconut oil fatty acid diethanolamide and sodium fluorosilicate according to a ratio; (2) mixing the binder in step (1) with 25% by weight of solvent, stirring at 500 rpm for 8 min, adding a conductive agent, a dispersant, polyethylene glycol, coconut oil fatty acid diethanolamide, sodium fluorosilicate and the remaining solvent, mixing, and stirring at 500 rpm for 20 min to obtain a conductive paste; (3) The conductive slurry is coated on the surface of the current collector body by using a micro-concave coater, and a functional coating is formed after drying. The drying temperature is 100° C. and the drying time is 20 min to obtain a highly conductive current collector for a secondary battery.

[0030] Note: The current collector is aluminum foil; the thickness of the current collector is 17.5 μm, the thickness of the functional coating is 50 μm, and the density is 0.7 g / m 2 The conductive agent is a composition of conductive carbon black and graphene in a weight ratio of 1:3, and the particle size D50 is 15 μm. The binder is acrylic acid acrylonitrile resin, and the viscosity of acrylic acid acrylonitrile resin at room temperature (25° C.) is 2500 mPa·s. The dispersant is carboxymethyl cellulose. The solvent is deionized water.

[0031] Example 2-3 A highly conductive current collector for a secondary battery is different from Example 1 in that the weights of raw materials used to prepare the functional coating are as shown in Table 1.

[0032] Table 1 Raw materials used for preparing functional coatings in Examples 1-3 and their corresponding weights (kg / portion) Example 4 A highly conductive current collector for a secondary battery is different from that in Example 1 in that the current collector body is a carbon-coated aluminum foil.

[0033] Example 5 A highly conductive current collector for a secondary battery is different from that in Example 1 in that the thickness of the current collector body is 5 μm.

[0034] Example 6 A highly conductive current collector for a secondary battery is different from that in Example 1 in that the thickness of the current collector body is 30 μm.

[0035] Example 7 A highly conductive current collector for a secondary battery is different from that in Example 1 in that the conductive agent is conductive carbon black.

[0036] Example 8 A highly conductive current collector for a secondary battery is different from that in Example 1 in that the conductive agent is graphene.

[0037] Example 9 A highly conductive current collector for a secondary battery is different from that in Example 1 in that the particle size D50 of the conductive agent is 1 μm.

[0038] Example 10 A highly conductive current collector for a secondary battery is different from that in Example 1 in that the particle size D50 of the conductive agent is 30 μm.

[0039] Embodiment 11 A highly conductive current collector for a secondary battery is different from that in Example 1 in that the binder is a water-based epoxy resin.

[0040] Example 12 A highly conductive current collector for a secondary battery is different from that of Example 1 in that the viscosity of the acrylic acrylonitrile resin at room temperature is 3000 mPa·s.

[0041] Example 13 A highly conductive current collector for a secondary battery is different from that in Example 1 in that the viscosity of the acrylic acrylonitrile resin at room temperature is 3200 mPa·s.

[0042] Comparative Example Comparative Example 1 A highly conductive current collector for a secondary battery is different from Example 1 in that polyethylene glycol and sodium fluorosilicate are not used in the raw materials of the functional coating.

[0043] Comparative Example 2 A highly conductive current collector for a secondary battery is different from Example 1 in that coconut oil fatty acid diethanolamide and sodium fluorosilicate are not used in the raw materials of the functional coating.

[0044] Comparative Example 3 A highly conductive current collector for a secondary battery is different from Example 1 in that polyethylene glycol and coconut oil fatty acid diethanolamide are not used in the raw materials of the functional coating.

[0045] Comparative Example 4 A highly conductive current collector for a secondary battery is different from Example 1 in that polyethylene glycol is not used in the raw materials of the functional coating.

[0046] Comparative Example 5 A highly conductive current collector for a secondary battery is different from Example 1 in that coconut oil fatty acid diethanolamide is not used in the raw materials of the functional coating.

[0047] Comparative Example 6 A highly conductive current collector for a secondary battery is different from Example 1 in that sodium fluorosilicate is not used in the raw materials of the functional coating.

[0048] Comparative Example 7 A highly conductive current collector for a secondary battery is different from Example 1 in that polyethylene glycol, coconut oil fatty acid diethanolamide and sodium fluorosilicate are not used in the raw materials of the functional coating.

[0049] Performance Test Test Samples: The highly conductive current collectors for secondary batteries obtained in Examples 1-13 were used as test samples 1-13, and the highly conductive current collectors for secondary batteries obtained in Comparative Examples 1-7 were used as control samples 1-7.

[0050] Test method: (1) Surface resistance (mΩ) test: Use the surface resistance tester RT-1000 to measure the surface resistance of the high conductive current collector for secondary batteries; (2) Peel strength test (N / m) between functional coating and current collector body: the test was conducted on the highly conductive current collector for secondary batteries in accordance with the requirements of the test method for peel strength of adhesive tape in GB / T 2792-2014, and 3M tape was used; Take a high-conductivity current collector sample for a secondary battery, and perform the above test to obtain the initial surface resistance value and the peel strength value between the initial functional coating and the current collector body; simultaneously place the corresponding high-conductivity current collector sample for a secondary battery in a constant temperature alternating test box, with an initial temperature of 25°C, first increase the temperature to 55°C at 3°C / min, keep it warm for 10 minutes, then cool it to -10°C at 1°C / min, keep it warm for 5 minutes, then increase the temperature to 25°C at 2°C / min, and continue for 20 cycles. After that, perform the above test to obtain the resistance value after temperature change and the peel strength value between the functional coating and the current collector body after temperature change; Finally, the surface resistance increase rate and the peel strength loss rate are calculated, the surface resistance increase rate = (resistance value after temperature change - initial surface resistance value) / initial surface resistance value, the peel strength loss rate = (peel strength value between the initial functional coating and the current collector body - peel strength value between the functional coating and the current collector body after temperature change) / initial peel strength value between the functional coating and the current collector body. The greater the surface resistance increase rate and the peel strength loss rate, the worse the application stability of the high conductive current collector for secondary batteries. The tests of test samples 1-13 and control samples 1-7 were completed in turn, and the test results were recorded in the following Table 2.

[0051] Table 2 Test results of test samples 1-13 and control samples 1-7 It can be seen from Examples 1-3 and Comparative Examples 1-7 and Table 2 that the use of polyethylene glycol, coconut oil fatty acid diethanolamide and sodium fluorosilicate in the preparation of the functional coating can significantly improve the adhesion stability and conductivity stability of the high conductive current collector for secondary batteries when subjected to frequent temperature changes, and the resistance increase rate and peel strength loss rate obtained by the above test are both low; while if only any one or two of polyethylene glycol, coconut oil fatty acid diethanolamide and sodium fluorosilicate are used, although the adhesion stability and conductivity stability can be improved, the combined effect is limited, and they can only bring a simple superposition effect to each other, and only when the three are used in combination, can a significant improvement effect of 1+1>2 be brought.

[0052] Combining Example 1 and Example 7-8 with Table 2, it can be seen that when conductive carbon black and graphene are used in combination, the resistance increase rate and peel strength loss rate obtained in the test are significantly lower, indicating that the combination of conductive carbon black and graphene has a heat transfer regulating effect and can cope with temperature changes well; and when any one of conductive carbon black and graphene is used alone as a conductive agent, it is found that although the resistance increase rate and peel strength loss rate do not increase much, they also have a relatively obvious increase, indicating that the combination of conductive carbon black and graphene, in addition to its own effect, is also more suitable for the action system formed by polyethylene glycol, coconut oil fatty acid diethanolamide and sodium fluorosilicate, so that the obtained high conductive current collector for secondary batteries has a stable application effect.

[0053] It can be seen from Example 1 and Examples 11-13 and Table 2 that when acrylic acrylonitrile resin is used as an adhesive, the high conductive current collector for secondary batteries has excellent bonding stability and conductive stability under frequent temperature changes; at the same time, when the viscosity of acrylic acrylonitrile resin at room temperature is not higher than 3000 mPa·s, it can be more fully combined with other raw materials in the functional coating, so that the coordination between the raw materials can play an excellent effect, and when it exceeds 3000 mPa·s, it is found that both the resistance increase rate and the peel strength loss rate show a relatively obvious increase.

[0054] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A highly conductive current collector for a secondary battery, characterized in that: The invention comprises a current collector body and a functional coating disposed on the surface of the current collector body, wherein the functional coating is made of raw materials including the following parts by weight: Conductive agent 3-6 parts; 3-6 parts of dispersant; 3-8 parts of binder; 80-90 parts of solvent; 0.5-3 parts of polyethylene glycol; Coconut oil fatty acid diethanolamide 3-6 parts; Sodium fluorosilicate 0.1-0.5 parts.

2. The highly conductive current collector for a secondary battery according to claim 1, characterized in that: The current collector body is one of aluminum foil, copper foil, carbon-coated aluminum foil and carbon-coated composite foil.

3. The highly conductive current collector for a secondary battery according to claim 1, characterized in that: The conductive agent is a combination of any two or more of conductive carbon black, conductive graphite, graphene, carbon fiber and carbon nanotube.

4. The highly conductive current collector for a secondary battery according to claim 3, characterized in that: The conductive agent is a composition of conductive carbon black and graphene, and the particle size D50 is 1-30 μm.

5. The highly conductive current collector for a secondary battery according to claim 1, characterized in that: The binder is one or a combination of acrylic acid acrylonitrile resin, waterborne polyurethane, polytetrafluoroethylene, waterborne epoxy resin and waterborne alkyd resin.

6. The highly conductive current collector for a secondary battery according to claim 5, characterized in that: The binder is acrylic acid acrylonitrile resin, and the viscosity of the acrylic acid acrylonitrile resin at room temperature is not higher than 3000 mPa•s.

7. The highly conductive current collector for a secondary battery according to claim 1, characterized in that: The dispersant is one or a combination of carboxymethyl cellulose, carboxymethyl cellulose lithium salt, carboxymethyl cellulose sodium salt, polyvinyl pyrrolidone, polyalkylene oxide unsaturated monomer, DIS-730A, isopropyl alcohol solution and SDS-720.

8. The highly conductive current collector for a secondary battery according to claim 1, characterized in that: The solvent is one or a combination of deionized water, ethanol, isopropanol and n-butanol.

9. The highly conductive current collector for a secondary battery according to claim 1, characterized in that: The thickness of the current collector is 5-30 μm, and the surface density of the functional coating is not more than 0.7 g / m 2 .

10. The method for preparing a highly conductive current collector for a secondary battery according to claim 1, characterized in that: The following steps are involved: (1) preparing raw materials including a conductive agent, a dispersant, a binder, a solvent, polyethylene glycol, coconut oil fatty acid diethanolamide and sodium fluorosilicate according to a ratio; (2) after mixing the binder and part of the solvent in step (1), a conductive agent, a dispersant, polyethylene glycol, coconut oil fatty acid diethanolamide, sodium fluorosilicate and the remaining solvent are added and mixed to obtain a conductive paste; (3) The conductive slurry is coated on the surface of the current collector body and dried to form a functional coating to obtain a highly conductive current collector for a secondary battery.

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