Aqueous insulating paste and its use

Abstract

The present application provides an aqueous insulating slurry and its application. The slurry includes a resin binder, an inorganic filler, an additive, and water. The resin binder includes a water-dispersible copolymer, the copolymer including a hydrophilic structural unit derived from a hydrophilic monomer and a hydrophobic structural unit derived from a hydrophobic monomer, and the molar proportion of the hydrophilic structural unit in the copolymer is 10%-20%. The additive includes a high-temperature hydrophobically associating polymer soluble in water. The aqueous insulating slurry has a thixotropic index greater than or equal to 5 at 100°C, and its thixotropic index at 100°C is greater than its thixotropic index at room temperature. The above-mentioned slurry has good dispersibility at room temperature and poor fluidity at high temperatures. When it is seamlessly coated with an aqueous electrode active slurry and then baked, it is not easy to diffuse at the contact interface between the two.

Description

Technical Field

[0001] The present application relates to the technical field of slurry coating, and in particular to a water-based insulating slurry and its application. Background Art

[0002] In the coating industry, when two different aqueous slurries are seamlessly coated on the same plane, and then passed through a drying oven for high-temperature baking after coating, mutual diffusion will occur at the joints of the different coatings formed by the two slurries. For example, in the design of battery cells, in order to avoid short circuits between different cells after lamination, an insulating layer is generally seamlessly connected horizontally to the edge of the dressing of the negative active coating in the negative electrode sheet of the battery cell. When preparing the negative electrode sheet, the aqueous negative electrode slurry corresponding to the preparation of the negative active coating and the aqueous insulating slurry corresponding to the formation of the above-mentioned insulating layer are generally coated at the same time by a coating machine, and then dried together in a drying oven. However, in the process, it is very easy for the contact area of ​​the negative active coating and the insulating layer to have obvious mutual diffusion (see Figure 1 ). However, there is no relevant solution to this problem in the industry. Summary of the Invention

[0003] In view of this, the present application provides an aqueous insulating slurry and its application to solve the problem that conventional aqueous insulating slurry and aqueous negative electrode slurry are prone to mutual diffusion at the interface after seamless coating and baking.

[0004] In the first aspect, the present application provides an aqueous insulating slurry comprising a resin binder, an inorganic filler, an additive and water, wherein the resin binder comprises a water-dispersible copolymer, the copolymer comprising a hydrophilic structural unit derived from a hydrophilic monomer and a hydrophobic structural unit derived from a hydrophobic monomer, and the molar proportion of the hydrophilic structural unit in the copolymer is 10%-20%; the additive comprises a water-soluble high-temperature hydrophobic associating polymer; wherein the thixotropic index of the aqueous insulating slurry at 100°C is greater than or equal to 5, and the thixotropic index of the aqueous insulating slurry at 100°C is greater than the thixotropic index at room temperature.

[0005] In the aqueous insulating slurry provided in the first aspect of the present application, the combined use of the above-mentioned specific resin binder and specific additives can ensure that the overall dispersibility of the aqueous insulating slurry at room temperature is good, and its thixotropic index at high temperature is high, the slurry fluidity is poor, and the diffusion is significantly inhibited, thereby greatly reducing the diffusion phenomenon at the contact interface between the aqueous electrode active slurry and the aqueous electrode active slurry when it is seamlessly coated and baked.

[0006] In a second aspect, the present application provides a method for preparing an electrode sheet, comprising the following steps:

[0007] coating the current collector with the electrode active slurry and the water-based insulating slurry on at least one side surface of the current collector, so that the water-based insulating slurry is located at the coating edge of the electrode active slurry and is in contact with the electrode active slurry;

[0008] baking the current collector with the electrode active slurry and the water-based insulating slurry to convert the electrode active slurry into an electrode active layer and the water-based insulating slurry into an insulating coating layer, to obtain an electrode tab.

[0009] The preparation method of the electrode tab is simple, and due to the use of the water-based insulating slurry provided in the embodiments of the present application, the diffusion / interpenetration between the obtained insulating coating layer and the electrode active layer in contact with the insulating coating layer is less.

[0010] The third aspect of the present application further provides an electrode tab obtained by the preparation method of the second aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 Schematic diagram of the process of coating the current collector with the water-based electrode active slurry and the common water-based insulating slurry and the baking process.

[0012] Figure 2 Schematic diagram of the top view structure of the electrode tab provided in the embodiments of the present application.

[0013] Figure 3 Schematic diagram of the side view structure of the electrode tab provided in the embodiments of the present application.

[0014] Figure 4 Characterization diagram of the interpenetration of the coating layers of the water-based insulating slurry of Example 1 and the negative electrode active slurry coated seamlessly therewith after baking.

[0015] Figure 5 Characterization diagram of the interpenetration of the coating layers of the water-based insulating slurry of Comparative Example 1 and the negative electrode active slurry coated seamlessly therewith after baking.

[0016] Figures 6-13 Characterization diagram of the interpenetration of the coating layers of the water-based insulating slurry of Examples 2-9 and the negative electrode active slurry coated seamlessly therewith after baking.

[0017] Figure 14 Characterization diagram of the interpenetration of the coating layers of the water-based insulating slurry of Comparative Example 2 and the negative electrode active slurry coated seamlessly therewith after baking.

[0018] Figure 15 Characterization diagram of the interpenetration of the coating layers of the water-based insulating slurry of Comparative Example 4 and the negative electrode active slurry coated seamlessly therewith after baking. DETAILED DESCRIPTION

[0019] The technical solutions of the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application.

[0020] Referring to Figure 1 , Figure 1 A schematic diagram of the processes of coating the aqueous electrode active slurry 11 and the conventional aqueous insulating slurry 12 on the current collector 10 and the baking process is provided in the present application. The common aqueous electrode active slurry 11 can be an aqueous negative electrode slurry, for example, a slurry containing a graphite negative electrode active material, water, a binder and an optional conductive agent. The rheological properties of the above two slurries at the coating and baking temperatures are generally different, in particular, the viscosity of the conventional aqueous insulating slurry 12 becomes particularly low at high temperature, and when entering the baking oven, the conventional aqueous insulating slurry 12 is extremely easy to diffuse to the electrode active slurry 11, which affects the directional distribution and the conductivity and ion conductivity of the obtained electrode active layer. To solve this problem, the present application provides an aqueous insulating slurry.

[0021] Specifically, the aqueous insulating slurry provided by the embodiments of the present application comprises a resin binder, an inorganic filler, an additive and water, wherein the resin binder comprises a copolymer dispersible in water, the copolymer comprises hydrophilic structural units derived from hydrophilic monomers and hydrophobic structural units derived from hydrophobic monomers, and the molar proportion of the hydrophilic structural units in the copolymer is 10%-20%; the additive comprises a high-temperature hydrophobic association type polymer soluble in water; wherein the thixotropic index of the aqueous insulating slurry at 100°C is greater than or equal to 5, and the thixotropic index of the aqueous insulating slurry at 100°C is greater than the thixotropic index at room temperature.

[0022] In the above aqueous insulating slurry, the resin binder contained therein is a high-temperature hydrophobic association type resin dispersible in water at room temperature, which comprises a copolymer containing a certain amount of hydrophilic structural units, which can be dispersed in water at room temperature, for example, in the form of micelles, to ensure that an aqueous adhesive slurry system can be formed, and the copolymer also contains an appropriate amount of hydrophobic structural units (molar proportion of 80%-90%), which facilitates increasing the tendency of the hydrophobic structural units in different micelle structures to agglomerate with each other at high temperature (i.e., increasing the hydrophobic association phenomenon of the polymer at high temperature), thereby significantly reducing the flowability of the aqueous insulating slurry at high temperature; at the same time, in combination with the above-mentioned high-temperature hydrophobic association additive, the flowability of the aqueous insulating slurry at high temperature can be further ensured to be poor, and the thixotropic index of the aqueous insulating slurry at high temperature (such as 100°C) is higher and greater than the thixotropic index at room temperature, and the diffusion / permeation of the aqueous insulating slurry at high temperature is obviously hindered, thereby greatly reducing the problem of diffusion at the interface between the aqueous insulating slurry and the aqueous electrode active slurry during the baking process after seamless coating of the two slurries.

[0023] The above thixotropic index of the present application is tested as follows: 200 g of the water-based insulating paste is poured into a 200 mL plastic cup, and a Bookfild viscometer DV2THBTJ0 is used to test the ratio of the viscosity of the paste at a shear rate of 5 rpm to the viscosity at a shear rate of 50 rpm at room temperature (e.g., 25°C) (i.e., the thixotropic index at room temperature), and the ratio of the viscosity of the paste at a shear rate of 5 rpm to the viscosity at a shear rate of 50 rpm at 100°C (i.e., the thixotropic index at 100°C). In the present application, the above "soluble in water" and "dispersible in water" refer to room temperature. The "room temperature" can refer to any temperature in the range of 20-30°C, for example, 20°C, 22°C, 25°C, 28°C or 30°C, and 25°C is more common.

[0024] In some embodiments of the present application, the thixotropic index of the water-based insulating paste at 100°C is greater than or equal to 6, for example, in the range of 6.5-20. This is more conducive to reducing diffusion at the interface between the water-based insulating paste and the water-based electrode active paste after seamless coating.

[0025] In addition, it should be noted that the conventional water-based insulating paste generally has a higher thixotropic index at high temperature than at room temperature, while the above water-based insulating paste provided by the embodiments of the present application is the opposite, i.e., it has high thixotropy at high temperature, and the diffusion / penetration of the paste at high temperature is significantly hindered. In the embodiments of the present application, the thixotropic index of the water-based insulating paste at room temperature is greater than or equal to 3. At this time, the thixotropic index of the water-based insulating paste at room temperature is also greater than that of the conventional water-based insulating paste, so that the water-based insulating paste also has high thixotropy at room temperature, and the diffusion / penetration phenomenon at room temperature is less likely to occur, which can further ensure the diffusion width of the insulating coating obtained by baking the water-based insulating paste to the other coatings. Specifically, the thixotropic index of the water-based insulating paste at room temperature can be in the range of greater than or equal to 3 to less than 7.5.

[0026] The mole percentage of the hydrophilic structural unit in the copolymer described above is 10% to 20%, which can avoid the mole percentage of the hydrophilic structural unit being too low to reduce the dispersibility of the copolymer in an aqueous system at room temperature, and can also avoid the mole percentage of the hydrophilic structural unit being too high to affect the hydrophobic association of the copolymer at high temperature, thereby reducing the flowability of the water-based insulation slurry at high temperature, and the like. Specifically, the mole percentage of the hydrophilic structural unit in the copolymer is 10% to 20%, for example, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, and the like. In some embodiments of the present application, the mole percentage of the hydrophilic structural unit in the copolymer is 10% to 15%. At this time, the hydrophobic structural unit in the copolymer can better play a strong hydrophobic association at high temperature, and the polymer can also have good dispersibility in water at room temperature.

[0027] In embodiments of the present application, the copolymer is polymerized from raw materials including a hydrophilic monomer and a hydrophobic monomer. The mole percentage of the hydrophilic structural unit in the copolymer is substantially the same as the ratio of the mole amount of the hydrophilic monomer to the sum of the mole amounts of the hydrophilic monomer and the hydrophobic monomer. The hydrophilic monomer includes one or more of acrylic acid, methacrylic acid, sodium acrylate, sodium methacrylate, ammonium acrylate, ammonium methacrylate, lithium acrylate, and lithium methacrylate, and the hydrophobic monomer includes one or more of ethylene, propylene, and isobutylene.

[0028] In embodiments of the present application, the melting point of the resin binder is 77 to 95°C, and the melting index is 1 to 300 g / 10 min. In this way, the electrode plate formed by the above water-based insulation slurry can realize good adhesion between the insulation layer and the separator by means of the insulation layer containing the resin binder during the hot rolling process (the temperature is about 100°C) with the separator. In this way, it can be avoided that the melting point of the resin binder is too high to cause the melting degree to be too low and the melting index to be too low, so that the insulation layer does not play the adhesion role, and it can also be avoided that the melting point of the resin binder is too low to cause the insulation coating to solidify and adhere to the roller next to the baking channel just after the insulation coating is formed by the baking channel. In addition, when the melting index of the resin binder is too high, it can also reflect that the molecular weight is small, and the corresponding cohesive strength is low. When passing through the guide roller in the baking channel, the friction force is easy to damage the cohesion of the resin, and then the resin adheres to the roller, resulting in the phenomenon of insulation layer sticking to the roller.

[0029] Specifically, the resin binder can have a melting point of 78, 80, 82, 85, 86, 88, 90, 92, or 95°C, and can specifically have a melt index of 10 g / 10 min, 20 g / 10 min, 30 g / 10 min, 40 g / 10 min, 50 g / 10 min, 60 g / 10 min, 70 g / 10 min, 75 g / 10 min, or 80 g / 10 min. In some embodiments, the resin binder has a melting point of 85-90°C and a melt index of 30-80 g / 10 min. In this case, the insulating layer containing the resin binder can better balance good adhesion and non-stick roll properties.

[0030] The test method of the melt index can refer to the national standard GB / T 3682-2018, and the test temperature is 190°C and the weight of the weight is 2.16 kg.

[0031] In the embodiments of the present application, the auxiliary agent can be a high-temperature hydrophobic association polymer soluble in water, which specifically refers to a water-soluble polymer with a small amount of hydrophobic groups on the hydrophilic molecular chain of the polymer. The polymer mainly exhibits hydrogen bond association at room temperature, has high solubility in water, and the hydrogen bond can be opened at high temperature, and the hydrophobic groups can be aggregated to form association, thereby achieving the effect of thickening at high temperature. In the embodiments of the present application, the auxiliary agent includes one or more of hydroxypropyl methyl cellulose, high-temperature hydrophobic association polyacrylamide, and high-temperature hydrophobic association polyurethane. In some embodiments, the auxiliary agent is hydroxypropyl methyl cellulose. The hydrophobic association of this substance is more obvious at high temperature, and the thickening effect of the water-based insulating paste is obvious.

[0032] In the embodiments of the present application, the mass of the auxiliary agent is 0.1-8 wt% of the mass of the resin binder. In this case, the amount of the hydrophilic auxiliary agent is beneficial to improve the dispersibility of the resin binder in the water-containing system at room temperature, and can significantly improve the thixotropic index of the overall paste system at high temperature, and the flowability is significantly reduced. Specifically, the mass of the auxiliary agent can be 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.2 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.2 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, or 7.8 wt% of the mass of the resin binder.

[0033] In the embodiments of the present application, the weight fraction of the inorganic filler is 300-500 parts based on 100 parts by weight of the resin binder, and the weight fraction of water is 500-800 parts. In combination with the mass ratio of the aforementioned auxiliary agent to the resin binder, at this time, the water-based insulating paste contains 100 parts by weight of the resin binder, 0.1-8 parts by weight of the auxiliary agent, 300-500 parts by weight of the inorganic filler, and 500-800 parts by weight of water. The water-based insulating paste meeting the formula can have a higher high-temperature thixotropic index and normal-temperature thixotropic index, and less diffusion to the surroundings at normal temperature and high temperature, and meanwhile, the insulating coating formed by the water-based insulating paste can play a good insulating effect.

[0034] Specifically, the weight fraction of the inorganic filler can be 320 parts, 350 parts, 380 parts, 400 parts, 420 parts, 450 parts, 480 parts, or 500 parts, etc., compared to 100 parts by weight of the resin binder. In the embodiments of the present application, the inorganic filler is an inorganic insulating material, which can be specifically selected from one or more of bormite, alumina, zirconia, etc., but is not limited thereto.

[0035] The present application also provides a preparation method of an electrode tab. Referring to the above-mentioned Figure 1 process schematic (the difference is that the conventional water-based insulating paste 12 is not used) and Figures 2-3 structure schematic of the electrode tab, the preparation method of the electrode tab comprises the following steps:

[0036] The electrode active paste 11 and the water-based insulating paste of the present application are coated on at least one side surface of the current collector 10, so that the water-based insulating paste is located at the coating edge of the electrode active paste 11 and is in contact with the electrode active paste 11.

[0037] The current collector 10 with the electrode active paste 11 and the water-based insulating paste is baked, so that the electrode active paste 11 is converted into the electrode active layer 101 and the water-based insulating paste is converted into the insulating coating 102, to obtain the electrode tab 100.

[0038] In the present application, one side surface of the current collector 10 can be coated with the electrode active paste 11 and the water-based insulating paste provided in the embodiments of the present application, and then baked to form the electrode active layer 101 and the insulating coating 102 (as shown in Figure 3 The electrode active paste 11 and the water-based insulating paste provided in the embodiments of the present application can be coated simultaneously or sequentially, and the simultaneous coating is preferred, which can improve the work efficiency.

[0039] The current collector 10 can be selected according to the specific type of the electrode tab 100. For example, when the electrode tab 100 is a negative electrode tab, the current collector 10 can specifically be a copper foil, a copper alloy foil, a carbon-coated copper foil, a nickel foil, etc., and the electrode active paste 11 is specifically a negative electrode active paste, which can include a negative electrode active material, a binder, a negative electrode solvent, and an optional conductive agent. The negative electrode active material can include, but is not limited to, at least one of a carbon-based material (such as graphite, soft carbon, hard carbon, etc.), a silicon-based material (elemental silicon, silicon alloy, silicon oxide, silicon-carbon composite material). When the electrode tab 100 is a positive electrode tab, the current collector 10 can specifically be an aluminum foil, an aluminum alloy foil, a carbon-coated aluminum foil, etc., and the electrode active paste 11 is specifically a positive electrode active paste, which can include a positive electrode active material, a binder, a conductive agent, and a positive electrode solvent. In a lithium ion battery, the negative electrode solvent of the negative electrode active paste is usually water or a hydrophilic solvent, which is similar to the solvent of the above-mentioned water-based insulating paste. Therefore, the above-mentioned electrode tab 100 is generally a negative electrode tab. In other battery fields, the above-mentioned electrode tab 100 can be a positive electrode tab.

[0040] In the embodiments of the present application, the solvent of the electrode active paste 11 is the same as that of the above-mentioned water-based insulating paste, i.e., water. In this way, the two pastes with the same solvent are more likely to diffuse into each other. The present application is an improvement for such pastes that are more likely to diffuse, and the effect is more prominent.

[0041] In the embodiments of the present application, the baking is generally performed at a temperature of 110-140°C. The temperature of the baking is generally higher than the melting point of the above-mentioned resin binder.

[0042] In the embodiments of the present application, after the baking, the mutual penetration width between the insulating coating 102 and the electrode active layer 101 is not more than 0.5 mm. This can reflect the poor flowability of the above-mentioned water-based insulating paste of the present application at high temperatures, which is less likely to diffuse. Therefore, the mutual penetration width between the insulating coating 102 and the electrode active layer 101 made of the above-mentioned water-based insulating paste of the present application is low.

[0043] The above-mentioned method for preparing the electrode tab is simple in process. Since the above-mentioned water-based insulating paste of the present application is used, the diffusion / penetration between the obtained insulating coating and the electrode active layer in contact with the insulating coating is less, and at the same time, the edge of the electrode tab is endowed with good insulation, avoiding short circuit between adjacent electrode tabs after the electrode tabs are stacked.

[0044] The electrode tab 100 can be prepared by the preparation method of the electrode tab provided in the embodiments of the present application.

[0045] In the embodiments of the present application, the electrode active layer 101 and the insulating coating layer 102 are provided on the current collector 10 in the same layer, and the bottom surfaces of the two are coplanar. In some embodiments of the present application, the thickness of the electrode active layer 101 is the same as that of the insulating coating layer 102.

[0046] In the embodiments of the present application, the mutual penetration width of the insulating coating layer 102 and the electrode active layer 101 is not more than 0.5 mm. This reflects that the interface of the two adjacent coating layers is obvious, and the mutual penetration is less.

[0047] The embodiments of the present application also provide a secondary battery, which comprises the electrode tab 100 described above.

[0048] In some embodiments of the present application, the secondary battery can comprise a positive electrode tab, a negative electrode tab, and a separator and an electrolyte provided between the positive electrode tab and the negative electrode tab, wherein at least one of the positive electrode tab and the negative electrode tab comprises the electrode tab 100 described above in the embodiments of the present application. The secondary battery can be a lithium secondary battery, a sodium secondary battery, a potassium secondary battery, a magnesium secondary battery, an aluminum secondary battery, a zinc secondary battery, etc.

[0049] Since the secondary battery described above contains the electrode tab described above, the width, thickness, etc. abnormalities caused by the mutual penetration of the insulating coating layer 102 and the electrode active layer 101 can be avoided in the manufacturing process of the secondary battery, the mutual penetration area powder falling and the current collector breaking at the corresponding mutual penetration area in the manufacturing process such as rolling can be avoided, and the battery capacity loss caused by the mutual penetration can also be avoided. At the same time, the use of the electrode tab can make the electrode tab and the separator have good adhesion, which can ensure the stable operation of the battery pack and avoid the battery short circuit risk caused by the electrode tab misalignment in the battery vibration process.

[0050] The embodiments of the present application also provide a power consuming device. The power consuming device using the secondary battery described above can be a vehicle such as a car (e.g. an electric car), a ship, etc., or a 3C product (e.g. a mobile phone, a tablet computer, a smart bracelet), etc.

[0051] The technical solutions of the present application will be further described below in combination with a plurality of specific embodiments.

[0052] Embodiment 1

[0053] An aqueous insulating paste comprises the following components in parts by weight: resin binder (sodium ethylene-acrylic acid copolymer, the molar amount of hydrophilic monomer sodium acrylate accounts for 15% of the sum of the molar amount of sodium acrylate and the molar amount of hydrophobic monomer ethylene, the melting point of the resin binder is 90°C, and the melt index is 55 g / 10 min) 100 parts by weight, inorganic filler (specifically boehmite) 470 parts by weight, auxiliary agent (specifically hydroxypropyl methyl cellulose) 5.2 parts by weight, and water 660 parts by weight. The aqueous insulating paste has a thixotropy index at room temperature of 3.23 and a thixotropy index at 100°C of 10.56.

[0054] The aqueous insulating paste and a negative electrode active paste (containing graphite, sodium carboxymethyl cellulose, butadiene-styrene rubber, conductive carbon black, and water) are simultaneously coated on one side surface of a copper foil according to a dry film thickness of 120 μm, and the aqueous insulating paste is located at the edge of the application of the negative electrode active paste and is in seamless contact with the electrode active paste; then, the copper foil coated with the two pastes is sent into a baking tunnel for baking. After the baking is completed, an ultra-depth-of-field three-dimensional microscope is used to observe the interpenetration of the contact area between the insulating coating baked from the aqueous insulating paste and the negative electrode active coating baked from the negative electrode active paste (as shown in Figure 4 , the darker area in the middle of the gray scale (the area above the arrow in the figure) is the negative electrode active coating), and the width of the interpenetration area is measured to be 331.05 μm. Figure 4

[0055] Comparative Example 1

[0056] An aqueous paste comprises the following components in parts by weight: resin binder (same as in Example 1) 100 parts by weight, inorganic filler (specifically boehmite) 470 parts by weight, and water 660 parts by weight, and does not contain the auxiliary agent hydroxypropyl methyl cellulose. The paste has a thixotropy index at room temperature of 2.5 and a thixotropy index at 100°C of 1.1.

[0057] The aqueous paste of Comparative Example 1 and a graphite negative electrode paste are seamlessly coated according to the method described in Example 1, and after drying in a baking tunnel, the interpenetration of the contact area between the two pastes is observed, and the results are shown in Figure 5 .The lighter area in the middle of the gray scale is the insulating coating. Based on Figure 5 , it can be measured that the interpenetration width of the contact area between the two pastes is 821.752 μm. In combination with the above Figure 5 , it can be known that the aqueous insulating paste provided in the present application has poor fluidity when baked at high temperature, which provides resistance to the interpenetration of the paste at high temperature, and the diffusion of the insulating coating formed to the negative electrode active coating in contact with it is less. Figure 4 Example 2

[0058]

[0059] ​Example 2 differs from Example 1 in that the resin binder used is an ethylene-sodium acrylate copolymer in which the molar proportion of the hydrophilic monomer sodium acrylate is 13.5%, and the melting point of the resin binder is 91°C and the melt index is 34 g / 10 min.

[0060] Example 3

[0061] Example 3 differs from Example 1 in that the resin binder used is an ethylene-sodium acrylate copolymer in which the molar proportion of the hydrophilic monomer sodium acrylate is 12%, and the melting point of the resin binder is 93°C and the melt index is 25 g / 10 min.

[0062] Example 4

[0063] Example 4 differs from Example 1 in that the resin binder used is an ethylene-sodium acrylate copolymer in which the molar proportion of the hydrophilic monomer sodium acrylate is 10%, and the melting point of the resin binder is 95°C and the melt index is 16 g / 10 min. ， The auxiliary used is hydroxypropyl methylcellulose in an amount of 0.1 parts by weight.

[0064] Example 5

[0065] Example 5 differs from Example 1 in that the resin binder used is an ethylene-sodium acrylate copolymer in which the molar proportion of the hydrophilic monomer sodium acrylate is 20%, and the melting point of the resin binder is 78°C and the melt index is 280 g / 10 min.

[0066] Example 6

[0067] Example 6 differs from Example 1 in that the auxiliary used is hydroxypropyl methylcellulose in an amount of 3 parts by weight.

[0068] Example 7

[0069] Example 7 differs from Example 1 in that the auxiliary used is hydroxypropyl methylcellulose in an amount of 8 parts by weight.

[0070] Example 8

[0071] Example 8 differs from Example 1 in that the resin binder used is a copolymer of the hydrophilic monomer methacrylic acid lithium and the hydrophobic monomer ethylene, in which the molar proportion of the hydrophilic monomer is 15%. The melting point of the resin binder is 91°C and the melt index is 32 g / 10 min. The auxiliary used is high-temperature hydrophobically associating polyurethane in an amount of 0.2 parts by weight.

[0072] Example 9

[0073] Example 9 differs from Example 1 in that the resin binder used is a copolymer of hydrophilic monomer-ammonium acrylate and hydrophobic monomer-ethylene, in which the molar proportion of the hydrophilic monomer is 15%. The melting point of the resin binder is 89°C, and the melt index is 31 g / 10 min. The auxiliary used is a high-temperature hydrophobically associating polyacrylamide.

[0074] Comparative Example 2

[0075] Comparative Example 2 differs from Example 1 in that the hydroxypropyl methyl cellulose of Example 1 is replaced by a non-high-temperature hydrophobically associating thickening agent, such as sodium carboxymethyl cellulose.

[0076] Comparative Example 3

[0077] Comparative Example 3 differs from Example 1 in that the resin binder used is a sodium acrylate-ethylene copolymer, in which the molar proportion of the hydrophilic monomer sodium acrylate is 5%.

[0078] Comparative Example 4

[0079] Comparative Example 4 differs from Example 1 in that the resin binder used is a sodium acrylate-ethylene copolymer, in which the molar proportion of the hydrophilic monomer sodium acrylate is 25%.

[0080] The interpenetration of the insulating coating formed by the aqueous insulating slurry of each of Examples 2-9 and Comparative Examples 2 and 4 and the negative electrode active coating in contact therewith can be seen in Figures 6-15 , and the interpenetration width is summarized in Table 1 below. Among them, the resin binder used in Comparative Example 3 cannot be dispersed in water to form an aqueous slurry, so the interpenetration test cannot be performed. In addition, Table 1 also summarizes the thixotropic index of the aqueous insulating slurry of each of the above examples and comparative examples at room temperature and at 100°C.

[0081] Table 1

[0082]

[0083] From Table 1, it can be seen that the aqueous insulating slurry provided by the embodiments of the present application, by introducing a specific resin binder and a water-soluble high-temperature hydrophobically associating polymer auxiliary, can make the thixotropic index of the aqueous insulating slurry at 100°C be greater than 5, and greater than the thixotropic index at room temperature, so that the diffusion degree of the aqueous insulating slurry and the aqueous electrode active slurry at the contact interface of the two after seamless coating and baking is small. This can further facilitate the improvement of battery performance.

[0084] In addition, from the comparison between Example 1 and Comparative Example 2, it can be seen that when the auxiliary agent used is not a high-temperature hydrophobic association type thickening agent, the thixotropic index of the water-based insulating paste at high temperature is small, is lower than the thixotropic index at normal temperature, and is also not conducive to reducing the mutual penetration of the two coatings when baking. From the comparison between Comparative Examples 3-4 and Examples 1-5, it can be seen that when the mole ratio of the hydrophilic monomer in the resin binder is too high or too low (such as not within the range of 10%-20%), it is not conducive to ensuring good water dispersibility of the paste and high thixotropic index at high temperature; in addition, when the mole ratio of the hydrophilic monomer in the resin binder is preferably within 10%-15%, the water-based insulating paste has a higher high-temperature thixotropic index and the mutual penetration of the coating is less obvious.

[0085] The above-described examples only express several exemplary embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A water-based insulating slurry, characterized in that: For electrode pole pieces, the aqueous insulating paste includes a resin binder, an inorganic filler, an additive and water, wherein the resin binder includes a copolymer dispersible in water, the copolymer includes a hydrophilic structural unit derived from a hydrophilic monomer and a hydrophobic structural unit derived from a hydrophobic monomer, and the molar proportion of the hydrophilic structural unit in the copolymer is 10%-20%; the additive includes a high-temperature hydrophobic associating polymer soluble in water; wherein the thixotropic index of the aqueous insulating paste at 100°C is greater than or equal to 5, and the thixotropic index of the aqueous insulating paste at 100°C is greater than the thixotropic index at room temperature; the thixotropic index of the aqueous insulating paste at 100°C refers to the ratio of its viscosity at 100°C and a shear rate of 5 rpm to its viscosity at 100°C and a shear rate of 50 rpm, and the thixotropic index of the aqueous insulating paste at room temperature refers to the ratio of its viscosity at room temperature and a shear rate of 5 rpm to its viscosity at room temperature and a shear rate of 50 rpm; the room temperature is 20°C-30°C.

2. The aqueous insulating slurry according to claim 1, characterized in that The thixotropic index of the aqueous insulating slurry at room temperature is greater than or equal to 3.

3. The aqueous insulating slurry according to claim 1, wherein The mass of the auxiliary agent is 0.1-8 wt % of the mass of the resin binder.

4. The aqueous insulating slurry according to claim 1, characterized in that The resin binder has a melting point of 77-95° C. and a melt index of 1-300 g / 10 min.

5. The aqueous insulating slurry according to claim 1, wherein The hydrophilic monomer includes one or more of acrylic acid, methacrylic acid, sodium acrylate, sodium methacrylate, ammonium acrylate, ammonium methacrylate, lithium acrylate, and lithium methacrylate; the hydrophobic monomer includes one or more of ethylene, propylene, and isobutylene.

6. The aqueous insulating slurry according to claim 1, wherein The auxiliary agent includes one or more of hydroxypropyl methylcellulose, high temperature hydrophobically associating polyacrylamide, and high temperature hydrophobically associating polyurethane.

7. The aqueous insulating slurry according to any one of claims 1 to 6, characterized in that: Based on 100 parts by weight of the resin binder, the weight of the inorganic filler is 300-500 parts, and the weight of the water is 500-800 parts.

8. A method for preparing an electrode plate, characterized in that: The following steps are involved: Applying an electrode active slurry and the aqueous insulating slurry according to any one of claims 1 to 7 on at least one surface of the current collector, so that the aqueous insulating slurry is located at the edge of the electrode active slurry and in contact with the electrode active slurry; The current collector with the electrode active slurry and the aqueous insulating slurry is baked to convert the electrode active slurry into an electrode active layer and the aqueous insulating slurry into an insulating coating to obtain an electrode pole piece.

9. The preparation method according to claim 8, wherein The interpenetration width between the insulating coating and the electrode active layer does not exceed 0.5 mm.

10. An electrode plate, characterized in that: It includes a current collector and an electrode active layer arranged on at least one side surface of the current collector, and also includes an insulating coating arranged at the edge of the electrode active layer and in contact with the electrode active layer, wherein the electrode pole piece is prepared by the preparation method according to any one of claims 8-9.

11. A secondary battery, characterized in that: Including the electrode plate according to claim 10.

12. An electrical device, characterized in that: The secondary battery according to claim 11 is included.

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