Multilayer pole piece, preparation method thereof and secondary battery

Abstract

The invention discloses a multi-layer pole piece and a preparation method thereof and a secondary battery, the multi-layer pole piece comprises a current collector, a first coating coated on at least one surface of the current collector and a second coating arranged on the outer surface of the first coating, the first coating comprises a first active material, a dispersing agent and a first binder, and the second coating comprises a second active material, a dispersing agent and a second binder. The second coating comprises a second active material, a dispersing agent and a second binding agent, and the surface energy of the first binding agent is larger than that of the second binding agent. Compared with the prior art, the preparation cost of the multi-layer pole piece is relatively low, and the market competitiveness of the product is improved. Layering of the multi-layer pole piece is formed in the drying process of coating slurry, the multi-layer pole piece can spontaneously achieve migration and layering of the slurry, additional complex technology or equipment assistance is not needed, and due to the characteristic, production steps are simplified, the production period is greatly shortened, and the production efficiency is improved; and the accuracy and the stability of the layered structure are also ensured.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and in particular to a multilayer pole piece, a preparation method thereof, and a secondary battery. Background Art

[0002] In the evolution of lithium-ion battery technology, improving energy density has always been the core research and development direction. With the surge in demand for high-power applications such as electric vehicles and energy storage devices, the electrode coating process faces two challenges: on the one hand, it is necessary to increase the volume energy density by increasing the active material loading per unit area, but the loading exceeds the critical threshold (usually >15mg / cm 2 ), the charge transfer impedance increases exponentially, resulting in an intensified polarization effect and a decrease in cycle stability of more than 30%; on the other hand, the traditional single-layer coating system is difficult to take into account both high energy density and excellent ion transport performance.

[0003] Existing solutions generally adopt a double-layer coating architecture. Its technical principle is as follows: the upper layer is coated with a kinetically optimized material with high lithium ion conductivity to construct a three-dimensional conductive network to improve the interface charge transfer rate; the lower layer uses a high specific capacity active material to maximize the energy density. Electrochemical tests show that this structure can increase the battery power density by 25%-40% while maintaining an energy density of >260Wh / kg. However, this process has significant defects: it requires a dual slurry supply system and a precise layering control module, which increases the equipment modification cost by about 60%; insufficient interfacial bonding strength between layers can easily cause the active material to peel off, reducing the long-term cycle capacity retention rate by 8%-12%; in addition, the limited coating speed causes a drop in production efficiency of more than 35%.

[0004] Given the inherent limitations of existing double-layer coating technology in terms of cost, process complexity and interface stability, the development of new coating solutions that combine high performance and low cost has become an urgent need in the industry. Summary of the Invention

[0005] The object of the present invention is to provide a multi-layer pole piece with low preparation cost and high efficiency, wherein the coating slurry migrates spontaneously during the drying process to form layers.

[0006] In order to achieve this object, the present invention provides the following scheme:

[0007] A multilayer electrode is provided, comprising a current collector, a first coating coated on at least one surface of the current collector, and a second coating arranged on the outer surface of the first coating, wherein the first coating comprises a first active material, a dispersant, and a first binder, and the second coating comprises a second active material, a dispersant, and a second binder, and the surface energy of the first binder is greater than the surface energy of the second binder.

[0008] Preferably, the surface energy of the first binder is 35-48 mN / m; the surface energy of the second binder is 34.5-47 mN / m.

[0009] Preferably, it also includes an Nth coating layer sequentially arranged on the surface of the second coating layer, N≥3, the Nth coating layer includes an Nth active material, a dispersant and an Nth binder, and the surface energy of the Nth binder is less than the surface energy of the (N-1)th binder.

[0010] Preferably, the surface energy of the Nth binder is 34.5-45 mN / m.

[0011] Preferably, the first binder comprises at least one of fluoropolyacrylate, polyisooctyl acrylate, and bisphenol A epoxy resin;

[0012] Preferably, the second binder comprises at least one of fluoropolyacrylate, polyisooctyl acrylate, and bisphenol A epoxy resin;

[0013] Preferably, the Nth adhesive includes at least one of fluoropolyacrylate, poly(isooctyl acrylate), and bisphenol A epoxy resin.

[0014] Preferably, the first active material is at least one of graphite, silicon-carbon composite material, lithium titanate, hard carbon lithium cobalt oxide, lithium iron phosphate, lithium manganate, ternary material, and lithium nickel oxide;

[0015] Preferably, the second active material is at least one of graphite, silicon-carbon composite material, lithium titanate, hard carbon lithium cobalt oxide, lithium iron phosphate, lithium manganate, ternary material, and lithium nickel oxide;

[0016] Preferably, the Nth active material is at least one of graphite, silicon-carbon composite material, lithium titanate, hard carbon lithium cobalt oxide, lithium iron phosphate, lithium manganate, ternary material, and lithium nickel oxide.

[0017] Preferably, the mass ratio of the first coating layer to the second coating layer is 1:0.8-1.2.

[0018] The present invention also provides a method for preparing a multilayer electrode sheet, comprising the following steps:

[0019] Step 1: mixing a first active material, a dispersant and a first binder to obtain a first slurry;

[0020] Step 2: mixing the second active material, the dispersant and the second binder to obtain a second slurry;

[0021] Step three: mixing the first slurry and the second slurry to obtain a mixed slurry, coating the mixed slurry on a current collector, and drying to obtain a multilayer electrode sheet.

[0022] Preferably, the mixed slurry further includes an Nth slurry, the Nth slurry includes an Nth active material, a dispersant and an Nth binder; the surface energy of the Nth binder is smaller than the surface energy of the (N-1)th binder.

[0023] The present invention also provides a secondary battery comprising the multi-layer electrode sheet.

[0024] Compared with the prior art, the beneficial effect of the present invention is that the multilayer electrode of the present invention exhibits excellent capacity retention in electrochemical performance. In addition, the preparation cost of the multilayer electrode is relatively low, which effectively reduces the overall cost of the production process and improves the market competitiveness of the product. At the same time, the most important thing is that the stratification of the multilayer electrode is formed during the drying process of the coating slurry. The multilayer electrode can spontaneously realize the migration and stratification of the slurry without the need for additional complex processes or equipment assistance. This feature not only simplifies the production steps, is efficient and fast, greatly shortens the production cycle, and improves production efficiency, but also ensures the accuracy and stability of the layered structure, providing a strong guarantee for the performance optimization of the electrode. DETAILED DESCRIPTION

[0025] To make the technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0026] In the first aspect of the present invention, the present invention provides a multilayer electrode, comprising a current collector, a first coating coated on at least one surface of the current collector, and a second coating disposed on the outer surface of the first coating, wherein the first coating comprises a first active material, a dispersant, and a first binder, and the second coating comprises a second active material, a dispersant, and a second binder, wherein the surface energy of the first binder is greater than the surface energy of the second binder. The multilayer coating of the multilayer electrode utilizes the differences in solubility, polarity, etc. of different adhesives in solvents. During the coating curing process, as the solvent evaporates, the two-phase composition changes, and the surface tension of the adhesive film is different, the low surface energy component migrates to the air layer, and the high surface energy component gradually migrates to the substrate, ultimately forming a thermodynamically stable multifunctional coating.

[0027] In one embodiment of the present invention, the surface energy of the first adhesive is 35-48 mN / m; the surface energy of the second adhesive is 34.5-47 mN / m.

[0028] In one embodiment according to the present invention, an Nth coating layer is further provided sequentially on the surface of the second coating layer, where N ≥ 3. The Nth coating layer includes an Nth active material, a dispersant, and an Nth binder, and the surface energy of the Nth binder is less than the surface energy of the (N-1)th binder. According to the principle of spontaneous migration coating, the surface energy of the binder in the coating layer closer to the current collector is greater than the surface energy of the binder in the coating layer farther from the current collector.

[0029] In one embodiment of the present invention, the surface energy of the Nth adhesive is 34.5-45 mN / m.

[0030] In one embodiment of the present invention, the first adhesive includes at least one of fluoropolyacrylate, polyisooctyl acrylate, and bisphenol A epoxy resin;

[0031] In one embodiment of the present invention, the second adhesive includes at least one of fluoropolyacrylate, polyisooctyl acrylate, and bisphenol A epoxy resin;

[0032] In one embodiment of the present invention, the Nth adhesive includes at least one of fluoropolyacrylate, poly(isooctyl acrylate), and bisphenol A epoxy resin.

[0033] In one embodiment according to the present invention, the first active material is at least one of graphite, silicon-carbon composite material, lithium titanate, hard carbon lithium cobalt oxide, lithium iron phosphate, lithium manganate, ternary material, and lithium nickel oxide;

[0034] In one embodiment according to the present invention, the second active material is at least one of graphite, silicon-carbon composite material, lithium titanate, hard carbon lithium cobalt oxide, lithium iron phosphate, lithium manganate, ternary material, and lithium nickel oxide;

[0035] In one embodiment of the present invention, the Nth active material is at least one of graphite, silicon-carbon composite material, lithium titanate, hard carbon lithium cobalt oxide, lithium iron phosphate, lithium manganate, ternary material, and lithium nickel oxide.

[0036] In one embodiment of the present invention, the mass ratio of the first coating layer to the second coating layer is 1:0.8-1.2.

[0037] In a second aspect of the present invention, the present invention further provides a method for preparing a multilayer electrode sheet, comprising the following steps:

[0038] Step 1: mixing a first active material, a dispersant and a first binder to obtain a first slurry;

[0039] Step 2: mixing the second active material, the dispersant and the second binder to obtain a second slurry;

[0040] Step 3: Mix the first slurry and the second slurry to obtain a mixed slurry, apply the mixed slurry to the current collector, and dry it to obtain a multilayer electrode. The stratification of the multilayer electrode is formed during the drying process of the coating slurry. The multilayer electrode can spontaneously achieve slurry migration and stratification without the need for additional complex processes or equipment. This feature not only simplifies the production steps, is efficient and fast, greatly shortens the production cycle, and improves production efficiency, but also ensures the accuracy and stability of the layered structure, providing a strong guarantee for the performance optimization of the electrode.

[0041] In one embodiment of the present invention, the mixed slurry further includes an Nth slurry, which includes an Nth active material, a dispersant, and an Nth binder; the surface energy of the Nth binder is less than the surface energy of the (N-1)th binder.

[0042] In one embodiment of the present invention, in step three, the drying temperature is 60-100° C. and the drying time is 2-4 hours.

[0043] In a third aspect of the present invention, the present invention further provides a secondary battery comprising the above-mentioned multi-layer electrode sheet.

[0044] The present invention will be further described below through specific examples.

[0045] Example 1

[0046] A multilayer electrode comprises a current collector, a first coating layer coated on one surface of the current collector, and a second coating layer arranged on the outer surface of the first coating layer, wherein the first coating layer comprises a first active material, a dispersant, and a first binder, and the second coating layer comprises a second active material, a dispersant, and a second binder, wherein the surface energy of the first binder is greater than the surface energy of the second binder.

[0047] The preparation method of the multilayer electrode is as follows:

[0048] Step 1: Graphite A (secondary particles, specific capacity of 345 mAh / g), SP, CMC, SBR, and fluoropolyacrylate (surface energy of 34.5 mN / m) are mixed in a ratio of 94%: 1.5%: 1.5%: 1.5%: 1.5% to obtain a first slurry;

[0049] Step 2: Graphite B (primary particles, specific capacity of 353 mAh / g), SP, CMC, SBR, and bisphenol A epoxy resin (surface energy of 47.1 mN / m) are mixed in a ratio of 94%:1.5%:1.5%:1.5%:1.5% to obtain a second slurry;

[0050] Step 3: Mix the first slurry and the second slurry in a ratio of 1:1 to obtain a mixed slurry, apply the mixed slurry on the current collector, and bake in an oven at 80°C for 2 hours to obtain a multilayer electrode.

[0051] The multilayer electrode sheet is used as the negative electrode sheet, and is prepared into a roll core with a conventional positive electrode sheet and a separator. The roll core is placed in a battery shell, and an electrolyte is injected to obtain a button battery.

[0052] Example 2

[0053] A multilayer electrode sheet includes a current collector, a first coating layer coated on one surface of the current collector, a second coating layer disposed on the outer surface of the first coating layer, and a third coating layer disposed on the outer surface of the second coating layer. The first coating layer includes a first active material, a dispersant, and a first binder. The second coating layer includes a second active material, a dispersant, and a second binder. The third coating layer includes a third active material, a dispersant, and a third binder. The surface energy of the first binder is greater than the surface energy of the second binder, and the surface energy of the second binder is greater than the surface energy of the third binder.

[0054] The preparation method of the multilayer electrode is as follows:

[0055] Step 1: Graphite A (secondary particles, specific capacity of 345 mAh / g), SP, CMC, SBR, and fluoropolyacrylate (surface energy of 34.5 mN / m) are mixed in a ratio of 94%: 1.5%: 1.5%: 1.5%: 1.5% to obtain a first slurry;

[0056] Step 2: Graphite A and graphite B are mixed in a ratio of 1:1 to obtain graphite C. Graphite C, SP, CMC, SBR, and poly(2-ethylhexyl acrylate) are mixed in a ratio of 94%:1.5%:1.5%:1.5%:1.5% to obtain a second slurry.

[0057] Step 3: Graphite B (primary particles, specific capacity of 353 mAh / g), SP, CMC, SBR, and bisphenol A epoxy resin (surface energy of 47.1 mN / m) are mixed in a ratio of 94%:1.5%:1.5%:1.5%:1.5% to obtain a third slurry;

[0058] Step 3: Mix the first slurry, the second slurry and the third slurry in a ratio of 1:1:1 to obtain a mixed slurry, apply the mixed slurry on the current collector, and bake in an oven at 80°C for 2 hours to obtain a multilayer electrode.

[0059] The multilayer electrode sheet is used as the negative electrode sheet, and is prepared into a roll core with a conventional positive electrode sheet and a separator. The roll core is placed in a battery shell, and an electrolyte is injected to obtain a button battery.

[0060] Comparative Example 1

[0061] The preparation method of the multilayer electrode is as follows:

[0062] Step 1: Graphite A (secondary particles, specific capacity of 345 mAh / g), SP, CMC, and SBR are mixed in a ratio of 94%:1.5%:3%:1.5% to obtain a first slurry;

[0063] Step 2: Graphite B (primary particles, specific capacity of 353 mAh / g), SP, CMC, and SBR are mixed in a ratio of 94%:1.5%:3%:1.5% to obtain a second slurry;

[0064] Step 3: Apply the first slurry on the current collector and bake it in an oven at 80°C for 2 hours to form a first coating; apply the second slurry on the surface of the first coating and bake it in an oven at 80°C for 2 hours to form a second coating to obtain a multilayer electrode.

[0065] The multilayer electrode sheet is used as the negative electrode sheet, and is prepared into a roll core with a conventional positive electrode sheet and a separator. The roll core is placed in a battery shell, and an electrolyte is injected to obtain a button battery.

[0066] Comparative Example 2

[0067] The preparation method of the multilayer electrode is as follows:

[0068] Step 1: Graphite A (secondary particles, specific capacity of 345 mAh / g), SP, CMC, and SBR are mixed in a ratio of 94%:1.5%:3%:1.5% to obtain a first slurry;

[0069] Step 2: Graphite A and graphite B are mixed in a ratio of 1:1 to obtain graphite C. Graphite C, SP, CMC, SBR, and poly(2-ethylhexyl acrylate) are mixed in a ratio of 94%:1.5%:1.5%:1.5%:1.5% to obtain a second slurry.

[0070] Step 3: Graphite B (primary particles, specific capacity of 353 mAh / g), SP, CMC, SBR, and bisphenol A epoxy resin (surface energy of 47.1 mN / m) are mixed in a ratio of 94%:1.5%:1.5%:1.5%:1.5% to obtain a third slurry;

[0071] Step 4: Apply the first slurry on the current collector and bake it in an oven at 80°C for 2 hours to form a first coating; apply the second slurry on the surface of the first coating and bake it in an oven at 80°C for 2 hours to form a second coating; apply the third slurry on the surface of the second coating and bake it in an oven at 80°C for 2 hours to form a third coating to obtain a multilayer electrode.

[0072] The multilayer electrode sheet is used as the negative electrode sheet, and is prepared into a roll core with a conventional positive electrode sheet and a separator. The roll core is placed in a battery shell, and an electrolyte is injected to obtain a button battery.

[0073] The button cells of the embodiment and the comparative example were respectively subjected to electrical performance tests, and the test results are shown in Table 1.

[0074] Table 1

[0075]

[0076] As can be seen from Table 1, the data of Examples 1 to 2 are better than those of Comparative Examples 1 to 2. The comparative example adopts a layered dry coating method to achieve a layered electrode structure, so there will be obvious interface incompatibility between the layers, which will cause the ion and electron transfer impedance of the electrode to increase during the charge and discharge process, and deteriorate the electrochemical performance; the embodiment adopts a mixed slurry coating, and the slurry forms a self-layered structure during the drying process. Its layered interface has better compatibility than the comparative example, which is more conducive to the ion and electron transfer during the charge and discharge process, so its electrochemical performance is better.

[0077] Based on the disclosure and teachings of the above description, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments. Any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention fall within the scope of protection of the present invention. In addition, although certain specific terms are used in this description, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A multi-layer pole piece, characterized in that: It includes a current collector, a first coating coated on at least one surface of the current collector, and a second coating arranged on the outer surface of the first coating, the first coating including a first active material, a dispersant and a first binder, the second coating including a second active material, a dispersant and a second binder, and the surface energy of the first binder is greater than the surface energy of the second binder.

2. The multilayer pole piece according to claim 1, characterized in that: The surface energy of the first binder is 35 to 48 mN / m; the surface energy of the second binder is 34.5 to 47 mN / m.

3. The multi-layer pole piece according to claim 1, characterized in that: It also includes an Nth coating layer sequentially arranged on the surface of the second coating layer, N≥3, the Nth coating layer includes an Nth active material, a dispersant and an Nth binder, and the surface energy of the Nth binder is less than the surface energy of the (N-1)th binder.

4. The multi-layer pole piece according to claim 3, characterized in that: The surface energy of the Nth binder is 34.5 to 45 mN / m.

5. The multi-layer pole piece according to claim 3, characterized in that: The first binder includes at least one of fluoropolyacrylate, polyisooctyl acrylate, and bisphenol A epoxy resin; And / or, the second binder includes at least one of fluoropolyacrylate, poly(isooctyl acrylate), and bisphenol A epoxy resin; And / or, the Nth adhesive includes at least one of fluoropolyacrylate, poly(isooctyl acrylate), and bisphenol A epoxy resin.

6. The multi-layer pole piece according to claim 3, characterized in that: The first active material is at least one of graphite, silicon-carbon composite material, lithium titanate, hard carbon lithium cobalt oxide, lithium iron phosphate, lithium manganate, ternary material, and lithium nickel oxide; and / or, the second active material is at least one of graphite, silicon-carbon composite material, lithium titanate, hard carbon lithium cobalt oxide, lithium iron phosphate, lithium manganate, ternary material, and lithium nickel oxide; And / or, the Nth active material is at least one of graphite, silicon-carbon composite material, lithium titanate, hard carbon lithium cobalt oxide, lithium iron phosphate, lithium manganate, ternary material, and lithium nickel oxide.

7. The multi-layer pole piece according to claim 1, characterized in that: The mass ratio of the first coating layer to the second coating layer is 1:0.8-1.

2.

8. A method for preparing a multilayer electrode according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: mixing a first active material, a dispersant and a first binder to obtain a first slurry; Step 2: mixing the second active material, the dispersant and the second binder to obtain a second slurry; Step three: mixing the first slurry and the second slurry to obtain a mixed slurry, coating the mixed slurry on a current collector, and drying to obtain a multilayer electrode sheet.

9. The method for preparing a multi-layer electrode according to claim 8, characterized in that: The mixed slurry further includes an Nth slurry, which includes an Nth active material, a dispersant, and an Nth binder; the surface energy of the Nth binder is smaller than the surface energy of the (N-1)th binder.

10. A secondary battery, characterized in that: A multilayer pole piece comprising the multilayer pole piece according to any one of claims 1 to 7 or a multilayer pole piece prepared by the method for preparing the multilayer pole piece according to any one of claims 8 to 9.

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