A positive electrode sheet with a polymer edge insulating layer and its application in lithium battery

Abstract

The present invention relates to the field of battery pole pieces. Aiming at the problem that the ceramic insulating layer of the battery pole piece has high hardness, wears the pressure roller, and is easy to peel off, a positive pole piece with a polymer edge insulating layer and its application in lithium batteries is provided. The polymer material is a polymer coating or tape, and the polymer coating is a polyimide polymer, an acrylic polymer, or a thermoplastic fluorine-containing polymer; the tape is a polyimide tape or PET tape resistant to high temperatures above 250°C. Compared with the ceramic insulating layer, the polymer coating or tape used in the present invention has the characteristics of low hardness, low surface roughness, and high bonding strength, which solves the problem that the ceramic insulating layer wears the pressure roller and peels off in layers.

Description

Technical Field

[0001] The invention relates to the field of battery pole pieces, and in particular to a positive pole piece with a polymer edge insulating layer. Background Art

[0002] After die-cutting, metal burrs are prone to appear on the edge of the positive electrode of lithium batteries. When the burrs pierce the diaphragm, they will directly conduct with the negative electrode, which may cause the risk of lithium battery fire and explosion. A 3-15mm wide ceramic insulation layer is coated on the edge of the positive electrode. After die-cutting, a 3-5mm wide insulation layer will remain on the positive electrode, making the width of the positive electrode sheet exceed the width of the negative electrode sheet. After winding or laminating, the edge of the negative electrode faces the residual insulation layer of the positive electrode, thereby avoiding the safety risk of conduction between the positive and negative electrodes through the die-cutting burrs. The insulation layer is mainly formed by using an integrated die head with an insulation layer coating function to simultaneously coat the insulation slurry on the edge of the positive electrode sheet during positive electrode coating. The insulation slurry is mainly made of ceramics, binders and organic solvents by stirring. Among them, ceramics are mostly aluminum oxide or boehmite (γ-AlOOH), and the proportion in the solid content of the slurry is between 80-95%; the binder is mostly polyvinylidene fluoride (PVDF, (CH 2 CF 2 ) n ), the proportion of which in the solid content of the slurry is between 5-20%; the organic solvent is mostly N-methylpyrrolidone (NMP, C 5 H 9 NO), the solid content of the insulating slurry is between 20-40%. For example, patent CN106784848B discloses an insulating coating composition, a method for preparing an insulating coating, a positive electrode sheet and a lithium ion battery, wherein the composition comprises an insulating material, a binder and a solvent, the insulating material is a ceramic material, the binder is polyvinylidene fluoride with a characteristic viscosity of not less than 2.2 dl / g, and the solvent is N-methylpyrrolidone.

[0003] Due to the high hardness of the ceramic particles or the sharp particle morphology (the Mohs hardness of aluminum oxide is about 9, and the commonly used boehmite particles are square in shape), the positive electrode with a ceramic edge insulation layer is severely worn by the insulation layer on the roller during the rolling process. In addition, since the ceramic insulation layer is a coating bonded by ceramic and a binder, the coating will crack due to force during the metal die-cutting or laser die-cutting process, and layered or flaky peeling will occur, resulting in insulation failure, thus affecting battery safety; ceramic powder will also fall off the edge of the insulation coating after die-cutting, and the detached ceramic will enter the battery, causing the risk of puncturing the diaphragm. Therefore, an ideal solution is needed. Summary of the invention

[0004] In order to overcome the problems that the ceramic insulating layer of the battery electrode has high hardness, wears the pressure roller and is easy to peel off, the present invention provides a positive electrode with a polymer edge insulating layer, and uses a polymer coating or tape to replace the ceramic insulating layer. It has the characteristics of low hardness, low surface roughness and high bonding strength, and solves the problems that the ceramic insulating layer wears the pressure roller and peels off in layers.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A positive electrode sheet with a polymer material edge insulating layer, wherein the polymer material is a polymer coating or tape, wherein the polymer coating is a polyimide polymer, an acrylic polymer or a thermoplastic fluorine-containing polymer; and the tape is a polyimide tape or a PET tape resistant to high temperatures above 200°C. Compared with a ceramic insulating layer, the polymer coating or tape used in the present invention has the characteristics of low hardness, low surface roughness and high bonding strength, thus solving the problem of wear of the pressure roller and lamellar peeling of the ceramic insulating layer.

[0007] Preferably, the edge insulation layer has a thickness of 15-60 μm and a width of 3-15 mm.

[0008] Preferably, the polyimide polymer is commercially available PI glue, the acrylic polymer is polyacrylic acid, and the thermoplastic fluorine-containing polymer is polyvinylidene fluoride.

[0009] Preferably, the preparation method of the acrylic polymer is:

[0010] (1) mixing three monomers of hydroxyethyl acrylate, toluene diisocyanate and 3-(methacryloyloxy)propyltrimethoxysilane in a molar ratio of (1.4-2):1:(0.8-1), adding hexadecanol, and stirring until completely dissolved to obtain an oil phase mixture;

[0011] (2) dissolving an emulsifier in water and stirring to obtain an aqueous phase mixture, wherein the mass concentration of the emulsifier is 3-5%, and the mass ratio of the total mass of the monomers in step (1) to water is 1:(1.8-2.5);

[0012] (3) adding the oil phase mixture to the water phase mixture, heating to 40-50° C., and ultrasonically emulsifying the mixture;

[0013] (4) The finely emulsified mixture is heated to 70-80° C. while being stirred under nitrogen protection, and sodium bisulfite and potassium persulfate are added and reacted for 6-8 hours to obtain an acrylic polymer.

[0014] The present invention adopts the mini-emulsion polymerization method to copolymerize acrylate, isocyanate and silicone. On the basis of maintaining the original adhesive properties of acrylate, isocyanate is used as a hard segment to enhance the strength and hardness of the polymer, so that the polymer has both rigidity and flexibility, and can adapt to the swelling and thermal contraction of the insulating layer in the battery. The amount of silicone used should comprehensively consider the impact on the emulsion and the impact on the polymer performance. On the one hand, silicone can improve the thermal stability and water resistance of the emulsion, but too much will cause the aggregation of colloid particles and reduce the stability of the emulsion. On the other hand, it can also improve the adhesion of the polymer to the pole piece, but too high a content will affect the mechanical properties of the polymer segment, so the quality of silicone should be controlled within a reasonable range.

[0015] Preferably, the coating process of the polymer coating on the positive electrode sheet comprises the following steps:

[0016] 1) Install the bracket on the coating back roller of the coating machine and fix the dispensing head on the bracket;

[0017] 2) The polymer coating slurry is injected into the glue sprayer, and after the slurry is squeezed to the glue dispensing head through the glue sprayer, the slurry is sprayed on the edge of the coated positive electrode to form an insulating coating, and the electrode is baked. After the solvent in the slurry is dried, a polymer film is formed, namely the edge insulating layer.

[0018] Preferably, the polymer content in the slurry in step 2) is 10-60wt%, and the solvent used is methanol, ethanol, ether, chloroform, pyridine, NMP or acetone.

[0019] Preferably, in step 2), the insulating coating has a thickness of 15-60 μm and a width of 3-11 mm after drying.

[0020] Preferably, the baking temperature in step 2) is 60-150°C.

[0021] Preferably, the process of applying the adhesive tape to the positive electrode sheet comprises the following steps: installing a adhesive tape mechanism on the roller after the coater comes out of the oven; applying the adhesive tape, i.e., the edge insulation layer, to the edge of the coated and baked positive electrode sheet by the adhesive tape mechanism.

[0022] Preferably, the tape has a width of 4-15 mm and a thickness of 25-50 μm.

[0023] Preferably, the adhesive laminating mechanism is provided with a self-contained adhesive tape changing device. Automatically changing the film roll can improve production efficiency.

[0024] The present invention also provides application of the positive electrode sheet with the polymer edge insulating layer in a lithium battery.

[0025] Therefore, the beneficial effects of the present invention are as follows: (1) The present invention adopts a polymer coating or tape, which has the characteristics of low hardness, low surface roughness and high bonding strength compared with the ceramic insulating layer, thereby solving the problems of wear of the pressure roller and layered peeling of the ceramic insulating layer; (2) The present invention adopts a mini-emulsion polymerization method to copolymerize acrylate, isocyanate and silicone. On the basis of maintaining the original bonding performance of acrylate, isocyanate is used as a hard segment to enhance the strength and hardness of the polymer, so that the polymer has both rigidity and flexibility, and can adapt to the swelling and thermal contraction of the insulating layer in the battery. Silicone can improve the bonding force of the polymer to the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a positive electrode sheet with an edge insulating layer, in which: 1, positive electrode sheet, 2, edge insulating layer;

[0027] Figure 2 It is a polymer coating coating process diagram;

[0028] Figure 3 This is a process diagram for gluing the tape insulation layer. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below through specific embodiments.

[0030] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments, unless otherwise specified, are all conventional methods in the art.

[0031] Example 1

[0032] A positive electrode sheet with a polymer material edge insulating layer, wherein the polymer material is a polymer coating, and the raw material of the polymer coating is polyacrylic acid. The slurry of the polymer coating is prepared by dispersing polyacrylic acid in acetone to form a slurry of 50wt%.

[0033] The coating process of the polymer coating on the positive electrode sheet is as follows Figure 2 As shown:

[0034] 1) Install a bracket on the coating back roller of the coating machine, fix the dispensing head on the bracket, determine the number of dispensing heads according to the number of insulating layers, determine the position of the dispensing head according to the size of the electrode, and select the corresponding model of dispensing head according to the width and thickness of the insulating layer. In this embodiment, the number of insulating layers is 2, the width of the insulating layer is 8 mm, and the thickness is 40 μm;

[0035] 2) The polymer coating slurry is injected into the glue tank of the glue machine, and the slurry is squeezed downward by the pressure plate on the upper part of the glue tank. After the slurry is squeezed to the glue dispensing head, the slurry is sprayed on the positive electrode sheet that has been coated but not baked. The slurry at the edge of the electrode sheet and the unbaked electrode sheet are put into a 100°C oven for baking. After the solvent in the slurry is dried, a polymer film is formed, that is, the edge insulation layer 2 of the positive electrode sheet 1, as shown in FIG. Figure 1 shown.

[0036] The positive electrode sheet is manufactured through subsequent steps according to the existing lithium battery production process to form a lithium battery.

[0037] Example 2

[0038] The difference from Example 1 is that the raw material of the polymer coating is a polyacrylic acid polymer, and the preparation method thereof is as follows:

[0039] (1) mixing three monomers, hydroxyethyl acrylate, toluene diisocyanate, and 3-(methacryloyloxy)propyltrimethoxysilane, in a molar ratio of 1.5:1:1, adding 1% by weight of hexadecanol to the mixture, and stirring until the mixture is completely dissolved to obtain an oil phase mixture;

[0040] (2) dissolving an emulsifier (sodium dodecylbenzene sulfonate and dodecylphenol polyoxyethylene ether-10 in a mass ratio of 2:1) in water and stirring to obtain an aqueous phase mixture, wherein the mass concentration of the emulsifier is 4%, and the mass ratio of the total mass of the monomers in step (1) to water is 1:2;

[0041] (3) adding the oil phase mixture to the water phase mixture, heating to 45°C, and ultrasonically emulsifying the mixture under the following ultrasonic conditions: ultrasonic power 500W, ultrasonic frequency 33kHz, and ultrasonic time 15min;

[0042] (4) The finely emulsified mixture was heated to 75° C. under nitrogen protection while being stirred, and 0.6% of the total weight of the monomers sodium bisulfite and 0.4% of potassium persulfate were added and reacted for 7 hours to obtain an acrylic polymer.

[0043] Example 3

[0044] The difference from Example 2 is that in step (1), the three monomers of hydroxyethyl acrylate, toluene diisocyanate and 3-(methacryloyloxy)propyltrimethoxysilane are mixed in a molar ratio of 1.5:1.3:1.

[0045] Example 4

[0046] The difference from Example 2 is that in step (1), the three monomers of hydroxyethyl acrylate, toluene diisocyanate and 3-(methacryloyloxy)propyltrimethoxysilane are mixed in a molar ratio of 1.5:1:1.3.

[0047] Example 5

[0048] A positive electrode sheet with a polymer material edge insulating layer, wherein the polymer material is an adhesive tape, and the adhesive tape is a polyimide adhesive tape resistant to high temperatures above 200°C.

[0049] The adhesive tape is applied to the positive electrode sheet as follows: Figure 3 As shown: a gluing mechanism is installed on the roller after the coating machine exits the oven. The number of gluing mechanisms is determined according to the number of insulating layers, and the gluing position is determined according to the size of the electrode. Tapes of different thicknesses and widths are selected to meet the size requirements of different insulating layers. In this embodiment, the number of insulating layers is 2, the width of the insulating layer is 10 mm, and the thickness is 30 μm. The gluing mechanism is used to stick tape on the edge of the coated and baked positive electrode, i.e., the edge insulating layer. The gluing mechanism is equipped with a self-contained tape changing device to automatically change the film roll to ensure production efficiency.

[0050] The positive electrode sheet is manufactured through subsequent steps according to the existing lithium battery production process to form a lithium battery.

[0051] Comparative Example 1

[0052] The difference from Example 1 is that there is no insulating layer on the positive electrode sheet.

[0053] Comparative Example 2

[0054] The difference from Example 1 is that the insulating layer on the positive electrode sheet is a ceramic insulating layer in the prior art.

[0055] Comparative Example 3

[0056] The difference from Example 2 is that toluene diisocyanate monomer is not added in step (1).

[0057] Comparative Example 4

[0058] The difference from Example 2 is that no 3-(methacryloyloxy)propyltrimethoxysilane monomer is added in step (1).

[0059] Performance Testing

[0060] 1. The service life of the battery chrome-plating roller when rolling the positive electrode sheet without an insulating layer of comparative example 1 and the positive electrode sheets with a polymer insulating layer of embodiments 1 and 5 is more than 1 million meters, while the service life is reduced by more than 50% when rolling the lithium iron phosphate positive electrode sheet with a ceramic insulating layer of comparative example 2.

[0061] 2. Conduct a yield test on the positive electrode sheets prepared in the above embodiments and comparative examples. Immerse them in an electrolyte (a conventional lithium salt-containing electrolyte) to measure the change in the adhesion of the non-ceramic insulating layer before and after immersion, as well as the effect of the insulating coating on the service life of the battery roller.

[0062]

[0063] As can be seen from the table, the electrode yield of Examples 1 and 5 of the present invention is improved compared with Comparative Examples 1 and 2, because the polymer insulating layer has good buffering performance compared with the ceramic insulating layer, and the damage to the electrode is minimal during the slitting and rolling process. From the perspective of the bonding strength of the insulating layer, the degree of decrease in the bonding strength of Example 1 after immersion in the electrolyte for 48 hours is lower than that of Comparative Example 2; Example 2 is modified relative to Example 1. On the one hand, the introduction of silicone improves the bonding strength in the dry state. On the other hand, because the electrolyte system is very active, it has a swelling and corrosive effect on the polyacrylic acid in the polymer insulating layer of Example 1, which will lead to a decrease in bonding strength. Example 2 effectively inhibits the corrosion of the electrolyte on the polymer insulating layer through the mutual cooperation of the three monomers.

[0064] Compared with Example 2, Comparative Example 3 did not add toluene diisocyanate monomer, and the performance of the polymer insulating layer in inhibiting electrolyte corrosion was reduced; Comparative Example 4 did not add 3-(methacryloyloxy)propyltrimethoxysilane monomer, the adhesion of the polymer insulating layer was reduced, and the performance of inhibiting electrolyte corrosion was also slightly reduced; in Example 3, the toluene diisocyanate monomer was excessive, and the performance of the polymer insulating layer in inhibiting electrolyte corrosion was reduced, because the toluene diisocyanate monomer was used as a hard segment to adjust the strength of the polymer, and excessive use would reduce the toughness of the polymer; in Example 4, the 3-(methacryloyloxy)propyltrimethoxysilane monomer was excessive, which would also affect the polymer performance, causing the performance of the polymer insulating layer in inhibiting electrolyte corrosion to be reduced, so the amount of the three monomers needs to be controlled within a reasonable range to achieve the best effect.

[0065] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a positive electrode sheet with a polymer edge insulating layer, characterized in that: A polymer material is sprayed on the edge of the positive electrode to form an edge insulating layer, and the polymer material is an acrylic polymer coating; the acrylic polymer is prepared by mixing hydroxyethyl acrylate, toluene diisocyanate, and 3-(methacryloyloxy)propyltrimethoxysilane monomers in a molar ratio of 1.4-2:1:0.8-1, adding hexadecanol and stirring until completely dissolved to obtain an oil phase mixture; an emulsifier is dissolved in water, and stirring is performed to obtain an aqueous phase mixture, wherein the mass concentration of the emulsifier is 3-5%, and the mass ratio of the total monomer mass to the water mass is 1:1.8-2.5; the oil phase mixture is added to the aqueous phase mixture, and the mixture is heated to 40-50°C for ultrasonic fine emulsification; the mixture is stirred and heated to 70-80°C under nitrogen protection, and sodium bisulfite and potassium persulfate are added for reaction for 6-8 hours to obtain an acrylic polymer.

2. The method for preparing a positive electrode sheet with a polymer edge insulating layer according to claim 1, characterized in that: The edge insulating layer has a thickness of 15-60 μm and a width of 3-15 mm.

3. The method for preparing a positive electrode sheet with a polymer edge insulating layer according to claim 1, characterized in that: The coating process of the polymer coating on the positive electrode sheet comprises the following steps: 1) Install the bracket on the coating back roller of the coating machine and fix the dispensing head on the bracket; 2) Inject the polymer coating slurry into the glue dispenser, squeeze the slurry to the glue dispensing head through the glue dispenser, and then spray the slurry on the edge of the coated positive electrode to form an insulating coating. Bake the electrode, and the solvent in the slurry will dry to form a polymer film, i.e., the edge insulating layer.

4. The method for preparing a positive electrode sheet with a polymer edge insulating layer according to claim 3, characterized in that: Step 2) The polymer content in the slurry is 10-60wt%.

5. The method for preparing a positive electrode sheet with a polymer edge insulating layer according to claim 3, characterized in that: Step 2) The solvent used is methanol, ethanol, ether, chloroform, pyridine, NMP or acetone.

6. The method for preparing a positive electrode sheet with a polymer edge insulating layer according to claim 3, 4 or 5, characterized in that: Step 2) The baking temperature is 60-150°C.

7. Use of a positive electrode sheet with a polymer edge insulating layer obtained by any preparation method of claims 1-6 in a lithium battery.

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