Composite foil and method for its production, processing equipment

Abstract

The application provides a composite foil and a preparation method and processing equipment thereof. The preparation method of the composite foil comprises the following steps: S1. coating a conductive paste on at least one surface of the foil to form a conductive layer; S2. performing thinning treatment on the edge of the conductive layer, performing first pre-drying on the conductive layer in the width direction of the conductive layer to obtain a semi-finished product; S3. coating an insulating paste on the edge of the conductive layer of the semi-finished product to form an insulating layer, and performing second drying to obtain the composite foil. The composite foil prepared by the method provided by the application solves the problem that the positive and negative active material layers directly contact each other to cause internal short circuit of the battery due to heat shrinkage of the diaphragm at high temperature, solves the problem of glue fusion between the conductive layer and the insulating layer during preparation of the composite foil, ensures the quality and production efficiency of the composite foil, and does not need to design an empty foil area between the conductive layer and the insulating layer, thereby ensuring the function of the insulating layer and reducing the internal short circuit risk of the battery using the composite foil provided by the application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a composite foil and a preparation method and processing equipment thereof. BACKGROUND

[0002] With the increasing application of lithium ion batteries in the fields of electric vehicles and grid energy storage, the safety performance of lithium ion batteries has been paid more and more attention. At present, the safety performance of lithium ion batteries has become one of the important factors restricting the rapid development of lithium ion batteries. Lithium ion batteries may occur thermal shrinkage of the separator under high temperature, the width of the overhang region of the separator beyond the positive and negative electrodes becomes smaller or even negative, resulting in direct contact of the positive and negative active material layers, and internal short circuit of the battery, thereby reducing the safety performance of the lithium ion battery. SUMMARY

[0003] In order to solve the problem of internal short circuit of the battery caused by thermal shrinkage of the separator under high temperature, and improve the safety performance of the battery, the present application provides a composite foil and a preparation method and processing equipment thereof.

[0004] According to a first aspect of the present application, a preparation method of a composite foil is provided, comprising the following steps:

[0005] S1. Coating a conductive paste on at least one surface of the foil to form a conductive layer;

[0006] S2. Thinning the edge of the conductive layer, and performing first pre-drying on the conductive layer along the width direction to obtain a semi-finished product;

[0007] S3. Coating an insulating glue paste on the edge of the conductive layer of the semi-finished product to form an insulating layer, and performing second drying to obtain the composite foil;

[0008] The temperature of the first pre-drying is T1, the time is t1, the temperature of the second drying is T2, and the time is t2, T1, T2, t1, t2 satisfy T1=(0.8-1.2)XT2, t1=(0.01-0.5)Xt2.

[0009] The prior art reduces the risk of direct contact of the positive and negative active material layers caused by thermal shrinkage of the separator under high temperature, thereby improving the safety performance of the battery.

[0010] In order to simplify the processing technology of the pole piece, the processing flow of the insulating glue is arranged in advance to the processing of the foil, that is, the insulating glue is coated in advance to form an insulating layer on the edge of the carbon coating layer (that is, the conductive layer) of the carbon-coated aluminum foil. In order to improve the production efficiency, the carbon coating layer and the insulating glue of the carbon-coated foil are selected to be coated and then baked and formed at one time. However, this will cause the carbon coating paste and the insulating glue paste to mutually melt and glue at the contact position before being baked and dried, so that the boundary between the two is not clear, and the edge cannot be recognized by the die cutting system when the pole piece is cut into the tabs in the subsequent process, which will cause the cutting error and affect the production yield.

[0011] In the preparation method of the composite foil provided by the present application, firstly, after forming the conductive layer by coating the conductive paste on the surface of the foil, the edge of the conductive layer is thinned to make the edge part of the conductive layer thinner, that is, the paste amount per unit area of the edge part of the conductive layer is less, then the conductive layer on the surface of the foil is pre-dried in the width direction of the conductive layer (i.e. the first pre-drying), because the paste surface density of the edge part of the conductive layer is lower after the thinning treatment, the paste of the edge part of the conductive layer is more easily dried, at this time the area of the edge of the conductive layer after the thinning treatment has been completely dried, then the insulating layer is formed by coating the insulating glue on the edge of the conductive layer, even if the conductive layer and the insulating layer are in contact and overlap, after the second drying, the conductive layer and the insulating layer will not have the problem of glue fusion, and for the area of the edge of the conductive layer which has not been thinned, it has not reached the state of complete drying, and the solid content of the conductive layer gradually decreases from the edge to the middle after the first pre-drying, which reduces the generation of stress difference between the conductive layer and the insulating layer in the preparation process of the composite foil, and can effectively avoid the problem of dry cracking of the conductive layer after the second drying; secondly, compared with heating the edge of the conductive layer alone, the first pre-drying is mainly for the thinned area of the conductive layer, which can ensure uniform heating in the width of the foil, ensure consistent heating of the foil in the width direction, make the internal stress of the conductive layer more uniform, and avoid the situation that the edge of the composite foil curls and the conductive layer cracks due to uneven internal stress of the conductive layer caused by heating the edge of the conductive layer alone, thereby improving the quality of the composite foil; thirdly, by controlling the temperature and time of the first pre-drying and the second drying within the above range, the thinned area of the conductive layer can be pre-dried, which not only avoids the problem of glue fusion during the drying process after the insulating glue paste is coated on the conductive layer, but also does not affect the flatness of the insulating glue paste when it is coated on the conductive layer, and the time of the first pre-drying is relatively short, thereby improving the production efficiency of the composite foil. Through the combined action of the above three aspects, the problems of direct contact between the positive and negative active material layers caused by the thermal shrinkage of the separator at high temperature, the glue fusion between the conductive layer and the insulating layer and the generation of stress difference in the preparation process of the composite foil, and the quality and production efficiency of the composite foil are solved, and at the same time, there is no need to design an empty foil area between the conductive layer and the insulating layer, which further ensures the function of the insulating layer, reduces the risk of internal short circuit of the battery using the composite foil provided by the present application, and improves the safety performance of the battery.

[0012] Preferably, T1 = (0.9-1.0) x T2.

[0013] Preferably, T2 = 80-110℃.

[0014] Preferably, t1 = (0.04-0.2) x t2.

[0015] Preferably, t2 = 0.05-0.15 min.

[0016] By optimizing the temperature and time of the first pre-drying, the production efficiency of the composite foil can be further improved while further improving the problem of glue melting between the conductive layer and the insulating layer during the drying process.

[0017] If the temperature of the first pre-drying is too high, the edge of the conductive layer cannot be cooled in time and the temperature is too high, causing the insulating glue paste to dry and set before it is coated on the edge of the conductive layer, affecting the coating flatness of the formed insulating layer. If the temperature of the first pre-drying is too low, the thinned area of the conductive layer will not be completely dried, and there will still be a risk of glue melting between the conductive layer and the insulating layer when the insulating glue paste is coated on the edge of the conductive layer. If the time of the first pre-drying is too long, it will also cause the temperature of the edge of the conductive layer to be too high, and the process of the first pre-drying will be too long, reducing the production efficiency of the composite foil.

[0018] Preferably, the conductive paste contains conductive carbon black.

[0019] Preferably, the insulating glue paste contains boehmite.

[0020] Preferably, in S3, during the process of coating the insulating glue paste on the edge of the conductive layer of the semi-finished product to form the insulating layer, it further includes the operation of thinning the insulating layer close to the edge of the conductive layer.

[0021] According to the second aspect of the present application, a composite foil is provided, which includes a foil and a conductive layer and an insulating layer arranged on the surface of the foil, the conductive layer includes a first main area and a first thinned area, the thickness of the first thinned area is less than the thickness of the first main area, and the first thinned area partially overlaps with the edge of the insulating layer.

[0022] In the composite foil provided in the present solution, the first thinned area in the conductive layer compounded on the surface of the foil partially overlaps with the edge of the insulating layer, so that the conductive layer and the insulating layer in the finally formed composite foil can be distinguished, and the boundary line of the two is clear, so that the tab of the composite foil applied in the present solution can be accurately recognized by the die cutting system when the tab is subsequently cut, avoiding the situation of mistaken cutting, and improving the production yield.

[0023] Preferably, the insulating layer includes a second main area and a second thinned area, the thickness of the second main area is less than the thickness of the second thinned area, and the first thinned area partially overlaps with the second thinned area.

[0024] Preferably, the thickness of the first thinned area decreases in the direction from the first main area to the first main area, and / or the thickness of the second thinned area decreases in the direction from the second main area to the second main area.

[0025] The above setting is conducive to natural transition of the thinning area and the main area of the conductive layer and the insulating layer in the composite foil, avoids the case that the protrusions at the junction of the thinning area and the main area of the conductive layer cannot completely cover the insulating layer or the protrusions at the junction of the thinning area and the main area of the conductive layer and the insulating layer are generated, and thus the active material layer in the pole piece using the composite foil is difficult to be well laminated, and the flatness of the active material layer in the pole piece during the coating process and the performance of the pole piece are affected.

[0026] Preferably, the width of the first thinning area is 1-10 mm, and / or the width of the second thinning area is 0.5-8 mm.

[0027] Preferably, the width of the second thinning area is A, the width of the insulating layer is B, and A, B satisfy 0.05≤A / B≤0.5.

[0028] By controlling the width of the first thinning area of the conductive layer and the second thinning area of the insulating layer within the above range, the overall flatness of the composite foil is ensured, and the flatness of the active material layer in the pole piece using the composite foil during the coating process and the performance of the pole piece are improved.

[0029] If the width of the first thinning area of the conductive layer is too wide, the overall flatness of the composite foil is affected; if the width of the first thinning area of the conductive layer is too narrow, the problem of unclear boundary with the insulating layer is prone to occur, and the production yield of the composite foil is affected.

[0030] If the width of the second thinning area of the insulating layer is too wide, the insulating layer is difficult to be stably laminated with the conductive layer, and thus the performance of the composite foil is affected; if the width of the second thinning area of the insulating layer is too narrow, the thickness of the overlapping area is prone to be too thick when overlapping with the first thinning area of the conductive layer, and thus the performance of the composite foil is affected.

[0031] According to a third aspect of the present application, a composite foil processing device is provided, which comprises a conductive layer coating device, an insulating layer coating device, a first pre-drying device and a second drying device; the conductive layer coating device comprises a conductive slurry coating roller, and the insulating layer coating device comprises an insulating glue slurry coating roller; the projection of the conductive slurry coating roller at least partially overlaps with the projection of the insulating glue slurry coating roller; the conductive slurry coating roller comprises a main coating area and a thinning coating area arranged in sequence, and the depth of the main coating area is greater than the depth of the thinning coating area.

[0032] Preferably, the conductive slurry coating roller is a gravure roller.

[0033] Preferably, the insulating glue slurry coating roller is a transfer coating roller.

[0034] Preferably, the insulating glue slurry coating roller comprises a planar coating area.

[0035] Preferably, the insulating paste material coating roller further comprises a thinning area, and the bottom surface of the thinning area protrudes from the planar coating area. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 A structure schematic diagram of the composite foil provided by the present application.

[0037] The reference signs are: 1 foil, 2 conductive layer, 2-1 first main area, 2-2 first thinning area, 3 insulating layer, 3-1 second main area, 3-2 second thinning area.

[0038] Figure 2 A process flow chart of the preparation of the composite foil provided by the present application. DETAILED DESCRIPTION

[0039] The technical features in the technical solutions provided by the present application will be further described clearly and completely in combination with the specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0040] Embodiment 1

[0041] A composite foil, the structure of which is shown in Figure 1 The composite foil comprises a foil 1 and a conductive layer 2 and an insulating layer 3 arranged on the surface of the foil 1. The conductive layer 2 comprises a first main area 2-1 and a first thinning area 2-2, the thickness of the first thinning area 2-2 is smaller than the thickness of the first main area 2-1, and the thickness of the first thinning area 2-2 gradually decreases along the direction from close to the first main area 2-1 to away from the first main area 2-1. The insulating layer 3 comprises a second main area 3-1 and a second thinning area 3-2, the thickness of the second main area 3-1 is smaller than the thickness of the second thinning area 3-2, and the thickness of the second thinning area 3-2 gradually decreases along the direction from close to the second main area 3-1 to away from the second main area 3-2. The first thinning area 2-2 and the second thinning area 3-2 overlap.

[0042] The composite foil of the present embodiment is processed by a composite foil processing device and refers to the structure schematic diagram of the composite foil provided by the present application. Figure 2The preparation process shown is prepared by using a composite foil processing device, which includes a conductive layer coating device, an insulating layer coating device, a first pre-drying device, and a second drying device; the conductive layer coating device includes a conductive slurry coating roller, and the insulating layer coating device includes an insulating adhesive slurry coating roller; the projection of the conductive slurry coating roller and the insulating adhesive slurry coating roller at least partially overlaps; the conductive slurry coating roller includes a main coating area and a thinning coating area arranged in sequence, and the depth of the main coating area is greater than the depth of the thinning coating area.

[0043] In the above-mentioned composite foil processing device, the conductive slurry coating roller is a gravure roller, and the insulating adhesive slurry coating roller is a transfer coating roller; the insulating adhesive slurry coating roller includes a planar coating area and can also include a thinning area, and the bottom surface of the thinning area protrudes from the planar coating area.

[0044] The preparation process of the composite foil provided in the embodiment is shown in Figure 2 The preparation process is prepared by the following steps:

[0045] S1. A foil 1 (empty foil) with a length of 12 μm and a width of 800 mm is placed in a composite foil processing device, and a conductive slurry containing carbon black is coated on both surfaces of the foil 1 by using a gravure coating roller (a conductive slurry coating device) with a groove width of 680 mm to form a conductive layer 2;

[0046] The gravure coating roller includes a planar coating area with a width of 660 mm and thinning areas with a width of 10 mm arranged on both sides of the planar coating area, and the groove depth of the planar coating area is 2 μm.

[0047] S2. The edges of the conductive layer 2 are thinned to divide the conductive layer into a first main area 2-1 and a first thinning area; during the coating of the conductive slurry by using the gravure coating roller, the planar coating area of the gravure coating roller can form the first main area 2-1, and the thinning areas on both sides of the gravure coating roller can form the first thinning area 2-2; a heating roller (a first pre-drying device) with an effective heating length of 0.5 m is used for first pre-drying to obtain a semi-finished product;

[0048] S3. A transfer coating roller (an insulating adhesive slurry coating device) is used to coat an insulating adhesive slurry containing boehmite on the first thinning area of the conductive layer of the semi-finished product to form an insulating layer, and a long oven (a second drying device) with a length of 5 m is used for second drying to obtain a composite foil;

[0049] The temperature T1 of the first pre-drying and the temperature T2 of the second drying are both 90℃, and T1 = 1.0 × T2.

[0050] The transfer coating roller is provided with a coating area in parallel contact with the projection of the gravure coating roller, and is arranged on both sides of the projection of the groove of the gravure coating roller. The coating width of both sides is 8mm, and the coating surface of the coating area is parallel to the foil.

[0051] The walking speed of the foil through the conductive paste coating device, the first pre-drying device, the insulating paste coating device and the second drying device is 90m / min, and the walking speed is uniform.

[0052] The time of the first pre-drying and the second drying is the effective heating length of the foil divided by the walking speed of the foil. The time t1 of the first pre-drying is 0.5m (the effective heating length of the heating roller) divided by 90m / min (the walking speed of the foil), which is 0.00556min. The time t2 of the second drying is 5m (the length of the long oven) divided by 90m / min (the walking speed of the foil), which is 0.0556min. t1=0.1×t2.

[0053] Example 2

[0054] The present embodiment provides a composite foil. Compared with Example 1, the difference is that the coating surface of the coating area of the transfer coating roller is a slope, the side close to the conductive layer protrudes from the side away from the conductive layer, the included angle with the foil is 1°, and the coating area on the transfer coating roller partially overlaps the projection of the gravure coating roller, and the single side overlapping width is 5mm. Except for the above differences, the materials, formula ratio and preparation operation adopted in the present embodiment are strictly consistent with those of Example 1.

[0055] Example 3

[0056] The present embodiment provides a composite foil. Compared with Example 1, the difference is that the first pre-drying device is a short oven with a length of 2m, the temperature T1 of the first pre-drying and the temperature T2 of the second drying are both 80℃, the walking speed of the foil is 100m / min, the time t1 of the first pre-drying is 2m (the effective heating length of the short oven) divided by 100m / min (the walking speed of the foil), which is 0.02min, T1=T2, and t1=0.36×t2. Except for the above differences, the materials, formula ratio and preparation operation adopted in the present embodiment are strictly consistent with those of Example 1.

[0057] Example 4

[0058] The present example provides a composite foil. Compared with Example 1, the difference is that the first pre-drying device is a heating roller with an actual heating length of 0.1 m, the first pre-drying temperature is 110°C, the first pre-drying time t1 = the effective heating length of the heating roller 0.1 m / the foil running speed 90 m / min = 0.0011 min; the second drying device is a long oven with a length of 10 m, the second drying temperature is 90°C, the second drying time t2 = the length of the long oven 10 m / the foil running speed 90 m / min = 0.1111 min; T1 = 1.22T1, t1 = 0.0099t2. Except for the above differences, the materials, formula, preparation operation and other conditions of the present example are strictly the same as those of Example 1.

[0059] Example 5

[0060] The present example provides a composite foil. Compared with Example 1, the difference is that the first pre-drying temperature T1 = 130°C, the second drying temperature T2 = 110°C, T1 = 1.18T2. Except for the above differences, the materials, formula, preparation operation and other conditions of the present example are strictly the same as those of Example 1.

[0061] Example 6

[0062] The present example provides a composite foil. Compared with Example 1, the difference is that the first pre-drying temperature T1 = 60°C, the second drying temperature T2 = 75°C, T1 = 0.8T2. Except for the above differences, the materials, formula, preparation operation and other conditions of the present example are strictly the same as those of Example 1.

[0063] Example 7

[0064] The present example provides a composite foil. Compared with Example 1, the difference is that the first pre-drying device is a heating roller with an actual heating length of 1.3 m, the first pre-drying time t1 = the effective heating length of the heating roller 1.3 m / the foil running speed 90 m / min = 0.0144 min, t1 = 0.26t2. Except for the above differences, the materials, formula, preparation operation and other conditions of the present example are strictly the same as those of Example 1.

[0065] Example 8

[0066] The present example provides a composite foil, which is compared with Example 1, and the difference is that the first pre-drying device is a heating roller with an actual heating length of 1.3 m, and the first pre-drying time t1 = the effective heating length of the heating roller 0.15 m / the foil running speed 90 m / min = 0.0017 min, t1 = 0.031 x t2. Except for the above difference, the materials, formula ratio and preparation operation used in the present example are strictly consistent with those of Example 1.

[0067] Comparative Example 1

[0068] The present comparative example provides a composite foil, which is compared with Example 1, and the difference is that the gravure coating roller (conductive paste coating device) is not provided with a thinning area, i.e. the conductive layer of the composite foil is not provided with a first thinning area, and no first pre-drying treatment is performed. Except for the above difference, the materials, formula ratio and preparation operation used in the present comparative example are strictly consistent with those of Example 1.

[0069] Comparative Example 2

[0070] The present comparative example provides a composite foil, which is compared with Example 1, and the difference is that the gravure coating roller (conductive paste coating device) is not provided with a thinning area, i.e. the conductive layer of the composite foil is not provided with a first thinning area, but the conductive layer is subjected to a first pre-drying treatment, and the coating area of the gravure coating roller and the transfer coating roller is arranged with an interval, and the interval on both sides is 3 mm. Except for the above difference, the materials, formula ratio and preparation operation used in the present comparative example are strictly consistent with those of Example 1.

[0071] Comparative Example 3

[0072] The present comparative example provides a composite foil, which is compared with Example 1, and the difference is that in the preparation step S2 of the composite foil, after the edge of the conductive layer is subjected to a thinning treatment, no first pre-drying treatment is performed. Except for the above difference, the materials, formula ratio and preparation operation used in the present comparative example are strictly consistent with those of Example 1.

[0073] Comparative Example 4

[0074] The present comparative example provides a composite foil, which is compared with Example 1, and the difference is that the gravure coating roller (conductive paste coating device) is not provided with a thinning area, i.e. the conductive layer of the composite foil is not provided with a first thinning area, and only the edge area of the conductive layer is subjected to a first pre-drying treatment, and the main body area is not subjected to a first pre-drying treatment. Except for the above difference, the materials, formula ratio and preparation operation used in the present comparative example are strictly consistent with those of Example 1.

[0075] Test Example

[0076] 1. Test subjects

[0077] The composite foil prepared in Examples 1-8 and Comparative Examples 1-4 was used in the preparation of a battery, and the battery was subjected to performance tests.

[0078] The battery was prepared according to the following steps:

[0079] (1) Preparation of a positive electrode sheet

[0080] A ternary positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, a binder polyvinylidene fluoride (PVDF), and a conductive agent carbon black (SP) were mixed in a mass ratio of 97:1.6:1.4, and then added to a solvent N-methyl pyrrolidone (NMP) to prepare a positive electrode slurry having a solid content of 45%. The positive electrode slurry was coated on both surfaces of a composite foil (an empty foil made of aluminum) to form a positive electrode active material, and then vacuum-dried to prepare a positive electrode sheet.

[0081] (2) Preparation of a negative electrode sheet

[0082] A negative electrode active material silicon-carbon material (10% by mass of silicon), an aqueous binder polyacrylic acid (PAA), and a conductive agent carbon nanotube were mixed in a mass ratio of 96:3:1, and then added to a solvent deionized water to prepare a negative electrode slurry having a solid content of 45%. The negative electrode slurry was coated on both surfaces of a negative electrode current collector copper foil having a thickness of 12 μm to form a negative electrode active coating layer, and then vacuum-dried to prepare a negative electrode sheet.

[0083] (3) Preparation of a separator

[0084] A polyethylene (PE) film having a ceramic layer on the surface was used as a separator, and the separator had a heat shrinkage temperature of 130°C.

[0085] (4) Preparation of an electrolyte

[0086] Vinyl carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed in a volume ratio of 1:1:1 to prepare an organic solvent, and then a fully dried lithium salt LiPF6 was dissolved in the organic solvent to prepare an electrolyte having a concentration of 1M.

[0087] (5) Assembly of a battery

[0088] The above positive electrode sheet, the separator, and the negative electrode sheet are stacked in order with the separator between the positive and negative electrode sheets to play a role of isolation, and then are wound to obtain a bare cell. The bare cell is placed in an outer packaging shell of an aluminum plastic film, and after drying, the above electrolyte is injected. After vacuum packaging, standing, formation, shaping, and other processes, the battery is obtained. In the battery, the edge of the negative active coating layer exceeds the edge of the positive active coating layer by 2 mm, and the separator exceeds the negative active coating layer by 5 mm.

[0089] 2. Test content

[0090] (1) Heat resistance test

[0091] At 25°C, the ACR of the above battery is tested by using an alternating current resistance tester. The internal resistance of the battery at this time is a1. Then, the battery is placed in a heating box at a constant temperature of 135°C for 30 min, taken out, cooled to room temperature, and then the ACR of the above battery is tested by using an alternating current resistance tester again. The internal resistance of the battery at this time is a2. The ACR reduction of the battery is calculated according to the following formula: ACR reduction (%) = (a1-a2) / a1x100%.

[0092] (2) Capacity test

[0093] At room temperature (25°C), the above battery is placed for 12 h. The battery is charged at a constant current of 0.1C rate to 4.2V, and the cutoff current is 0.05C. After 10 min, the battery is discharged at a constant current of 0.3C rate, and the cutoff voltage is 2.5V. The discharge capacity of the battery is recorded.

[0094] 3. Experimental results

[0095] Table 1. Related performance test results of the battery

[0096] Group a1 (mΩ) a2 (mΩ) ACR reduction (%) Capacity (mA) Example 1 6.4 6.5 -1.6 1885 Example 2 6.9 6.7 2.9 1871 Example 3 6.3 6.0 4.8 1877 Example 4 6.2 6.5 -4.8 1853 Example 5 6.4 5.8 9.4 1860 Example 6 6.8 6.5 2.9 1838 Example 7 6.4 6.2 4.7 1862 Example 8 6.3 6.7 -4.8 1849 Comparative Example 1 6.3 6.2 1.6 1703 Comparative Example 2 6.8 4.9 27.9 1875 Comparative Example 3 6.3 6.2 1.6 1750 Comparative Example 4 / / / /

[0097] The related performance test results of the battery of the composite foil prepared in application examples 1-8 and comparative examples 1-4 are shown in Table 1.

[0098] The composite foil provided in Examples 1-8 is prepared by first performing a thinning treatment on the edges of the conductive layer after forming the conductive layer by coating a conductive paste on the surface of the foil, so that the edge portion of the conductive layer is thinned, i.e., the amount of paste per unit area of the edge portion of the conductive layer is reduced, then the foil is pre-dried (i.e., first pre-drying), so that the paste of the edge portion of the conductive layer is dried, at this time the edge of the conductive layer is already dried, then an insulating adhesive is coated on the edge of the conductive layer to form an insulating layer, so that the conductive layer and the insulating layer are in contact and overlap, after re-drying (i.e., second drying), the conductive layer and the insulating layer do not have a glue fusion problem, and the boundary between the conductive layer and the insulating layer is clear. The composite foil prepared in Examples 1-8 is applied to the pole piece and the battery, the boundary between the conductive layer and the insulating layer is clear, which enables the die cutting system to better recognize the edge during subsequent pole piece die cutting, the actual effective area of the pole piece is controllable, the battery has a higher discharge capacity at 25°C, and the ACR reduction of the battery is lower, which indicates that the battery has good heat resistance, reduces the risk of internal short circuit when the battery has a thermal anomaly, and enables the battery to have good safety performance in actual application.

[0099] The composite foil provided in Example 2 is also thinned in the preparation process, and the insulating layer covers part of the thinned area of the conductive layer, which can reduce the risk of air gap between the insulating layer and the conductive layer due to equipment error, reduce the risk of internal short circuit of the battery, and improve the flatness of the foil after winding, reducing the risk of wrinkling during winding due to the large difference in thickness between the conductive layer and the insulating layer.

[0100] Compared with Example 1, the composite foil provided in Example 3 has a longer length and time of first pre-drying in the preparation process, resulting in a higher temperature of the conductive layer and incomplete cooling, at this time coating the insulating adhesive paste on the edge of the conductive layer will cause the insulating adhesive paste to dry and form before it is leveled, resulting in poor flatness of the formed insulating layer, and due to the longer first pre-drying time, the production efficiency is lower than that of Example 1.

[0101] Compared with Example 1, the composite foil provided in Example 4 has a shorter length of the heating roller and drying time of the first pre-drying in the preparation process, and the conductive layer and the insulating adhesive still have a partial glue fusion problem, with a glue fusion width of 0.5-1 mm.

[0102] Compared with Example 1, the composite foil provided in Examples 5-6 does not satisfy the two relationships of T1=(0.9-1.0) x T2 and / or T2=80-110°C in the first pre-drying temperature T1 and the second drying temperature T2 in the preparation process, and the first pre-drying temperature used in the preparation process of the composite foil in Example 5 is too high, and the temperature of the foil to the insulating adhesive coating process is too high, resulting in poor insulating adhesive flow, uneven coating, and local foil leakage. After heat resistance test, it is found that the internal resistance is reduced, which indicates that there may be internal short circuit. However, the first pre-drying temperature used in the preparation process of the composite foil in Example 6 is too low, and the drying of the thinned area is not complete, which may have a risk of glue melting. However, compared with no pre-drying, the boundary between the conductive layer and the insulating adhesive is relatively clear, and the edge effect of die cutting is smaller. The test results show that the ACR reduction of Examples 5-6 is higher than that of Example 1, and the capacity of the battery is lower than that of Example 1.

[0103] Compared with Example 1, the composite foil provided in Examples 7-8 does not satisfy the two relationships of t1=(0.04-0.2) x t2 and / or t2=0.05-0.15 min in the first pre-drying time t1 and the second drying time t2 in the preparation process. The test results show that the ACR reduction of Examples 7-8 is higher than that of Example 1, and the capacity of the battery is lower than that of Example 1.

[0104] Compared with Example 1, the composite foil provided in Comparative Example 1 does not have a thinned area in the gravure coating roller (conductive paste coating device) in the processing equipment used in the preparation process, and there is a serious glue melting problem between the conductive layer and the insulating layer during the drying process, with a glue melting width of 4-6 mm, which seriously affects the positioning and edge grabbing in the subsequent die cutting process, and the actual effective area of the electrode sheet is uncontrollable, which may eventually lead to a low capacity of the battery.

[0105] Compared with Example 1, the composite foil provided in Comparative Example 2 does not have a thinned area in the gravure coating roller (conductive paste coating device) in the processing equipment used in the preparation process, and the coating interval between the gravure coating roller and the transfer type coating roller is set, with a distance of 3 mm on both sides, resulting in a large number of exposed foil areas in the finally prepared composite foil. The battery using the composite foil of Comparative Example 2 is prone to internal short circuit when it is hot, which is specifically manifested in that the ACR reduction is significantly higher than that of Example 1, which significantly reduces the safety performance of the battery.

[0106] Compared with Example 1, the composite foil provided in Comparative Example 4 does not have a thinned area in the gravure coating roller (conductive paste coating device) used in the preparation process, i.e., the conductive layer of the composite foil does not have a first thinned area, and only the edge region of the conductive layer is subjected to the first pre-drying treatment, and the main body region is not subjected to the first pre-drying treatment. The surface of the conductive layer of the composite foil provided in Comparative Example 4 cracks at the two side preheating boundaries, and the foil is discarded and cannot be used to make electrodes and batteries.

[0107] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently, and these modifications or replacements are within the protection scope of the present application.

Claims

1. A method for preparing a composite foil, characterized in that, Includes the following steps: S1. Coating a conductive paste onto at least one surface of the foil to form a conductive layer; S2. The edges of the conductive layer are thinned, and the conductive layer is pre-dried for the first time along the width direction of the conductive layer to obtain a semi-finished product. After the first pre-drying, the area of ​​the conductive layer edge that has been thinned is completely dry, while the area of ​​the conductive layer edge that has not been thinned is not completely dry. S3. An insulating mortar is coated on the edge of the conductive layer of the semi-finished product to form an insulating layer. After a second drying, the composite foil is obtained. Let the temperature of the first pre-drying be T1 and the time be t1, and let the temperature of the second drying be T2 and the time be t2. T1, T2, t1, and t2 satisfy the following conditions: T1 = (0.9~1.0) × T2, T2 = 80~110℃, t1 = (0.04~0.2) × t2, and t2 = 0.05~0.15 min.

2. The method for preparing the composite foil as described in claim 1, characterized in that: The conductive paste contains conductive carbon black, and / or the insulating paste contains boehmite.

3. A composite foil prepared using the method as described in claim 1 or 2, characterized in that: The composite foil includes a foil and a conductive layer and an insulating layer disposed on the surface of the foil. The conductive layer includes a first main body region and a first thinned region. The thickness of the first thinned region is less than the thickness of the first main body region. The first thinned region overlaps with the edge portion of the insulating layer. The insulating layer includes a second main region and a second thinned region, the thickness of the second thinned region is less than the thickness of the second main region, and the first thinned region and the second thinned region partially overlap. The width of the first thinning zone is 1~10 mm, and the width of the second thinning zone is 0.5~8 mm; Let A be the width of the second thinning zone and B be the width of the insulating layer, wherein A and B satisfy 0.05≤A / B≤0.

5.

4. The composite foil as described in claim 3, characterized in that: The thickness of the first thinned region decreases along the direction from the first main body region to the direction away from the first main body region. And / or, The thickness of the second thinning region decreases along the direction from near the second main body region to far away from the second main body region.

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