Battery cell and lithium battery using same

Abstract

A battery cell, comprising a positive electrode sheet, a composite separator, and a negative electrode sheet which are arranged in sequence. The positive electrode sheet comprises a first positive electrode active coating; the negative electrode sheet comprises a first negative electrode active coating; the composite separator comprises a positive-electrode-side porous active layer and a negative-electrode-side porous active layer; the positive-electrode-side porous active layer comprises a non-binder polymer C1; the negative-electrode-side porous active layer comprises a non-binder polymer C2; the compacted density of the first positive electrode active coating is 2.05-3.60 g / cm3; the compacted density of the first negative electrode active coating is 1.40-1.85 g / cm3; the lamination of the positive electrode sheet and the composite separator is achieved by means of pressing treatment I; and the lamination of the negative electrode sheet and the composite separator is achieved by means of pressing treatment II.

Description

Battery cell and lithium battery using same

[0001] This application claims priority to Chinese Patent Application No. 202410544928.X, filed on April 30, 2024, and Chinese Patent Application No. 2024106225197, filed on May 17, 2024, the contents of which are incorporated herein by reference in their entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of lithium batteries, in particular to a battery cell and a lithium battery using the same. BACKGROUND

[0003] As a key material of lithium ion batteries, the main function of the separator is to isolate the positive and negative electrodes to avoid short circuiting caused by contact between the positive and negative electrodes. Meanwhile, the separator has a microporous structure, which can provide a channel for the movement of lithium ions. The material of the separator is generally polyethylene (PE) or polypropylene (PP). TECHNICAL PROBLEM

[0004] The PE and PP separators are not tightly attached to the electrode sheets, which can easily cause wrinkles in the electrode sheets, increase the internal resistance, and then cause a series of electrical performance and safety performance problems of the battery. TECHNICAL SOLUTION

[0005] In a first aspect, the present application provides a battery cell, comprising a positive electrode sheet, a composite separator and a negative electrode sheet arranged in sequence; the positive electrode sheet comprises a positive electrode current collector and a first positive electrode active coating layer, the first positive electrode active coating layer is arranged on the surface of the positive electrode current collector facing the composite separator; the negative electrode sheet comprises a negative electrode current collector and a first negative electrode active coating layer, the first negative electrode active coating layer is arranged on the surface of the negative electrode current collector facing the composite separator; the composite separator comprises a porous substrate layer, a positive electrode side porous active layer and a negative electrode side porous active layer, the surface of the porous substrate layer facing the positive electrode sheet is a first surface, the positive electrode side porous active layer is arranged on the first surface, the surface of the porous substrate layer facing the negative electrode sheet is a second surface, and the negative electrode side porous active layer is arranged on the second surface; the positive electrode side porous active layer comprises a first base coating layer and a non-binder polymer C1 embedded in the first base coating layer, the D 50 > thickness of the first base coating layer; the negative electrode side porous active layer comprises a second base coating layer and a non-binder polymer C2 embedded in the second base coating layer, the D 50 > thickness of the second base coating layer; the first positive electrode active coating layer has a compacted density of 2.05-3.60 g / cm 3 ; and the first negative electrode active coating layer has a compacted density of 1.40-1.85 g / cm 3The compounding of the positive electrode sheet and the composite separator is realized by a pressing treatment I, the pressing temperature T1 of the pressing treatment I satisfies 50℃≤T1 3 , 2.2g / cm 3 , 2.35g / cm 3 , 2.5g / cm 3 , 2.65g / cm 3 , 2.7g / cm 3 , 2.85g / cm 3 , 3.0g / cm 3 , 3.15g / cm 3 , 3.30g / cm 3 , 3.45g / cm 3 , 3.60g / cm 3 , etc., but not only limited to the listed values, other unlisted values within the value range are also applicable. The compaction density of the first negative electrode active coating can be 1.40g / cm 3 , 1.50g / cm 3 , 1.60g / cm 3 , 1.70g / cm 3 , 1.80g / cm 3 , 1.85g / cm 3 , etc., but not only limited to the listed values, other unlisted values within the value range are also applicable.

[0006] In a second aspect, the present application provides a lithium battery comprising the above-mentioned battery cell. Advantages

[0007] In the composite electrode provided in the present application, the first positive active coating layer with a specific compactness is arranged on the positive electrode sheet, the surface of the positive electrode sheet is relatively smooth and has fewer pores, and therefore, the non-binder polymer C1 is arranged to form a clear protruding structure on the surface of the porous active layer of the composite separator on the positive electrode side, and the composite separator is combined with the positive electrode sheet under the pressure bonding treatment I condition at a higher temperature, so that the protruding structure formed by the non-binder polymer C1 can be fully and effectively filled in the smaller pores on the surface of the positive electrode sheet, thereby realizing the close combination of the composite separator and the positive electrode sheet; meanwhile, the non-binder polymer C1 has a higher Tg value and excellent mechanical properties, which is beneficial to making the composite separator have sufficient structural stability and thermal stability; the first negative active coating layer with a specific compactness is arranged on the negative electrode sheet, the surface of the negative electrode sheet is relatively rough and has more pores, and therefore, the non-binder polymer C2 is arranged to form a clear protruding structure on the surface of the porous active layer of the composite separator on the negative electrode side, and the composite separator is combined with the negative electrode sheet under the pressure bonding treatment II condition at a lower temperature, so that the protruding structure formed by the non-binder polymer C2 can be easily inserted into the larger pores on the surface of the negative electrode sheet, thereby realizing the close combination of the composite separator and the positive electrode sheet.

[0008] In summary, the electrode provided in the present application can realize the stable and firm combination between the composite separator and the positive and negative electrode sheets by regulating the compactness of the first positive and negative active coating layers towards the composite separator, and further limiting the combination conditions of the composite separator and the positive and negative electrode sheets, thereby effectively improving the bonding effect of the composite separator and the positive and negative electrode sheets, and improving the structural stability and cycle stability of the electrode. Embodiments of the present application

[0009] In some embodiments, the non-binder polymer C1 is selected from one or more of poly(methyl acrylate), poly(ethyl acrylate), poly(butyl acrylate), poly(methyl methacrylate), butyl acrylate-styrene copolymer, ethylene-acrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-methyl methacrylate copolymer.

[0010] In some embodiments, the non-binder polymer C2 is selected from one or more of poly(methyl acrylate), poly(ethyl acrylate), poly(butyl acrylate), poly(methyl methacrylate), butyl acrylate-styrene copolymer, ethylene-acrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-methyl methacrylate copolymer.

[0011] In some embodiments, the D of the non-binder polymer C1 is 0.1-0.5. 50: the thickness of the first base coating layer = (1.3~4): 1. The D 50 : The thickness of the first base coating layer can be 1.3: 1, 2: 1, 2.7: 1, 3.4: 1, 4: 1, etc., but is not limited to the listed values, and other values not listed within the range are also applicable. By reasonably setting the D 50 : The ratio of the thickness of the first base coating layer, it is beneficial to ensure that the non-adhesive polymer C1 can be stably and firmly embedded in the first base coating layer of the composite separator, thereby further facilitating the stable and firm embedding of the protruding structure formed by the non-adhesive polymer C1 into the pores of the positive electrode sheet, thereby effectively improving the adhesion effect of the composite separator and the positive electrode sheet.

[0012] In some embodiments, the thickness of the first base coating layer is 1~4 μm, the D 50 of the non-adhesive polymer C1 is 3~7 μm, and the thickness of the first positive electrode active coating layer is 40~150 μm.

[0013] In some embodiments, the D 50 : The thickness of the second base coating layer = (1.3~4): 1. The D 50 : The thickness of the second base coating layer can be 1.3: 1, 2: 1, 2.7: 1, 3.4: 1, 4: 1, etc., but is not limited to the listed values, and other values not listed within the range are also applicable. By reasonably setting the D 50 : The ratio of the thickness of the second base coating layer, it is beneficial to ensure that the non-adhesive polymer C2 can be stably and firmly embedded in the second base coating layer of the composite separator, thereby further facilitating the stable and firm embedding of the protruding structure formed by the non-adhesive polymer C2 into the pores of the negative electrode sheet, thereby effectively improving the adhesion effect of the composite separator and the negative electrode sheet.

[0014] In some embodiments, the thickness of the second base coating layer is 1~4 μm, the D 50 of the non-adhesive polymer C2 is 3~7 μm, and the thickness of the first negative electrode active coating layer is 40~100 μm.

[0015] In some embodiments, the mass fraction (weight fraction) of the non-binder polymer C1 in the positive electrode side porous active layer is 3% to 22%. The mass fraction of the non-binder polymer C1 in the positive electrode side porous active layer can be 3%, 7%, 11%, 15%, 19%, 22%, etc., but is not limited to the listed values, and other values not listed in this range are also applicable. Since the above positive electrode sheet has a low porosity, by effectively controlling the content of the non-binder polymer C1 in the positive electrode side porous active layer, the surface of the composite separator has a sufficient amount of protruding structures, effectively increasing the probability of the non-binder polymer C1 embedding the first positive electrode active coating of the positive electrode sheet, thereby improving the fit between the composite separator and the positive electrode sheet; at the same time, the high-Tg non-binder polymer C1 with the above content can effectively ensure the thermal shrinkage performance and air permeability of the separator, so that the battery has excellent electrical performance and safety performance.

[0016] In some embodiments, the mass fraction (weight fraction) of the non-binder polymer C1 in the positive electrode side porous active layer is 17% to 22%.

[0017] In some embodiments, the mass fraction (weight fraction) of the non-binder polymer C2 in the negative electrode side porous active layer is 2% to 17%. The mass fraction of the non-binder polymer C2 in the negative electrode side porous active layer can be 2%, 5%, 7%, 9%, 11%, 13%, 15%, 17%, etc., but is not limited to the listed values, and other values not listed in this range are also applicable. Since the Tg value of the non-binder polymer C2 is relatively low, a large amount of non-binder polymer C2 can easily cause the thermal shrinkage rate of the composite separator to increase and the thermal stability to decrease, therefore, by further effectively controlling the content of the non-binder polymer C2 in the negative electrode side porous active layer, the low-Tg non-binder polymer C2 with a suitable content can not only ensure the excellent thermal shrinkage performance of the composite separator, but also ensure that the surface of the composite separator has a suitable amount of protruding structures, so that the fit between the composite separator and the negative electrode sheet remains at a high level.

[0018] In some embodiments, the mass fraction (weight fraction) of the non-binder polymer C2 in the negative electrode side porous active layer is 7% to 12%.

[0019] In some embodiments, the non-binder polymer C1 has a Tg value of 55-90°C. The non-binder polymer C1 can have a Tg value of 55°C, 65°C, 75°C, 85°C, 90°C, etc., but is not limited to the listed values, and other values not listed within the range are also applicable. The non-binder polymer C1 within the above Tg value range has good mechanical properties, and has sufficient elasticity during the compounding process of the composite separator and the positive electrode sheet to be fully inserted into the pores of the positive electrode sheet, thereby improving the adhesion of the composite separator and the positive electrode sheet, and the mechanical strength is high, thereby improving the thermal stability of the composite separator and the cycle stability of the battery.

[0020] In some embodiments, the non-binder polymer C2 has a Tg value of 30-90°C. The non-binder polymer C2 can have a Tg value of 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc., but is not limited to the listed values, and other values not listed within the range are also applicable. The non-binder polymer C2 within the above Tg value range is easily and stably inserted into the pores of the negative electrode sheet during the compounding process of the composite separator and the negative electrode sheet, thereby improving the adhesion of the composite separator and the negative electrode sheet.

[0021] In some embodiments, the non-binder polymer C2 has a Tg value of 30-53°C.

[0022] In some embodiments, the pressing temperature T1 of the pressing treatment I is 50-70°C, and the pressing pressure of the pressing treatment I is 0.2-14 tons (t); the pressing temperature T2 of the pressing treatment II is 28-48°C, and the pressing pressure of the pressing treatment II is 0.2-14 tons (t). The pressing temperature T1 of the pressing treatment I can be 50°C, 60°C, 70°C, etc., and the pressing pressure of the pressing treatment I can be 0.2 tons, 1 ton, 3 tons, 5 tons, 7 tons, 9 tons, 11 tons, 13 tons, 14 tons, etc., but is not limited to the listed values, and other values not listed within the range are also applicable. The pressing temperature T2 of the pressing treatment II can be 28°C, 38°C, 48°C, etc., and the pressing pressure of the pressing treatment II can be 0.2 tons, 1 ton, 3 tons, 5 tons, 7 tons, 9 tons, 11 tons, 13 tons, 14 tons, etc., but is not limited to the listed values, and other values not listed within the range are also applicable.

[0023] In some embodiments, the first positive electrode active coating layer comprises a first positive electrode active material, and the first positive electrode active material has a D50 value of 0.1-20 μm; the first negative electrode active coating layer comprises a first negative electrode active material, and the first negative electrode active material has a D50 value of 5-20 μm. 50 In some embodiments, the first positive electrode active coating layer comprises a first positive electrode active material, and the first positive electrode active material has a D50 value of 0.1-20 μm; the first negative electrode active coating layer comprises a first negative electrode active material, and the first negative electrode active material has a D50 value of 5-20 μm. 50 In some embodiments, the first positive electrode active coating layer comprises a first positive electrode active material, and the first positive electrode active material has a D50 value of 0.1-20 μm; the first negative electrode active coating layer comprises a first negative electrode active material, and the first negative electrode active material has a D50 value of 5-20 μm.

[0024] In some embodiments, the first positive active material comprises at least one of lithium iron phosphate, lithium iron manganese phosphate, a ternary material, lithium cobaltate, lithium manganate.

[0025] In some embodiments, the first negative active material comprises at least one of graphite, hard carbon, soft carbon, silicon-based material.

[0026] Example 1

[0027] The present example provides a lithium battery, and a preparation method thereof, which comprises the following steps:

[0028] 1. Preparing a positive electrode sheet:

[0029] The first positive active material (particle size D 50 is lithium iron phosphate with a particle size of 0.95 pm), a conductive agent, conductive carbon black SP, and a binder, polyvinylidene fluoride (PVDF), are mixed uniformly at a mass ratio of 94:3:3, dispersed in N-methyl pyrrolidone (NMP) to obtain a positive electrode slurry, the positive electrode slurry is coated on an aluminum foil, and the aluminum foil is dried at 85°C in a vacuum environment for 24 hours to obtain a positive electrode sheet.

[0030] The positive electrode sheet comprises a positive electrode current collector and a first positive active coating layer, and the compaction density of the first positive active coating layer is 2.45 g / cm 3 .

[0031] 2. Preparing a negative electrode sheet:

[0032] The first negative active material (particle size D 50 is graphite with a particle size of 12.5 pm), a conductive agent, conductive carbon black (SP), and a binder, sodium carboxymethyl cellulose (CMC), are mixed uniformly at a mass ratio of 92:4:4, dispersed in deionized water to obtain a negative electrode slurry, the negative electrode slurry is coated on a copper foil, and the copper foil is dried at 100°C in a vacuum environment for 12 hours to obtain a negative electrode sheet.

[0033] The negative electrode sheet comprises a negative electrode current collector and a first negative active coating layer, and the compaction density of the first negative active coating layer is 1.50 g / cm 3 .

[0034] 3. Preparing a separator:

[0035] S1. A porous substrate layer is prepared by adding a polyethylene (PE) porous substrate to a tank, extruding, casting, longitudinally stretching, extracting, and heat setting;

[0036] S2. Inorganic particles A, alumina, a binder polymer B, polyvinylidene fluoride, a non-binder polymer C1, butyl acrylate-styrene copolymer, are added to a stirring tank at a mass ratio of 76:4:20, and a solvent is added to stir and disperse uniformly, then dispersed at a stirring speed of 1000 rpm for 100 min to form a first coating slurry;

[0037] Inorganic particles A alumina, binder polymer B polyvinylidene fluoride, non-binder polymer C2 butyl acrylate-styrene copolymer were added into a stirring tank in a mass ratio of 86:4:10, and a solvent was added to stir and disperse uniformly, then dispersed continuously for 100 min at a stirring speed of 1000 rpm to form a second coating slurry;

[0038] S3, the first coating slurry was coated on the first surface of the porous substrate layer (the surface of the porous substrate layer facing the positive plate is the first surface) to form a positive side porous active layer; the positive side porous active layer comprises a first base coating and a non-binder polymer C1 embedded in the first base coating, wherein the thickness of the first base coating is 2.0 μm, the particle size D 50 of the non-binder polymer C1 is 5.1 μm, the mass fraction of the non-binder polymer C1 in the positive side porous active layer is 20%, and the Tg value of the non-binder polymer C1 is 60°C (the non-binder polymer C1 is composed of butyl acrylate-styrene copolymer, and the butyl acrylate-styrene copolymer is prepared from butyl acrylate and styrene in a molar ratio of 2.6:7.4).

[0039] S4, the second coating slurry was coated on the second surface of the porous substrate layer (the surface of the porous substrate layer facing the negative plate is the second surface) to form a negative side porous active layer; the negative side porous active layer comprises a second base coating and a non-binder polymer C2 embedded in the second base coating, wherein the thickness of the second base coating is 2.0 μm, the particle size D 50 of the non-binder polymer C2 is 5.1 μm, the mass fraction of the non-binder polymer C2 in the negative side porous active layer is 10%, and the Tg value of the non-binder polymer C2 is 40°C (the non-binder polymer C2 is composed of butyl acrylate-styrene copolymer, and the butyl acrylate-styrene copolymer is prepared from butyl acrylate and styrene in a molar ratio of 3.8:6.2).

[0040] S4, after coating, oven drying was performed, and a composite separator was prepared after drying.

[0041] 4, preparation of electrolyte:

[0042] Vinyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0043] 5, preparation of battery:

[0044] (1) Composite membrane and positive electrode composite: pressing treatment I (pressing temperature T1 is 52℃, pressing pressure is 1.2t, pressing time is 3s);

[0045] (2) Composite membrane and negative electrode sheet composite: pressing treatment II (pressing temperature T1 is 30℃, pressing pressure is 0.8t, pressing time is 1s);

[0046] (3) Prepare bare cells.

[0047] 6. Assemble lithium batteries

[0048] The bare cell is placed in an outer packaging shell, dried, and then injected with the above-mentioned electrolyte. After vacuum sealing, standing, formation, and volume adjustment, a lithium battery is prepared.

[0049] Example 2

[0050] This embodiment prepares a lithium battery according to Example 1. The difference between this embodiment and Example 1 is that the non-binder polymer C1 used in this embodiment has a D... 50 The thickness is 10 μm. Apart from the differences mentioned above, the materials and processes used in this embodiment are strictly consistent with those in Example 1.

[0051] Example 3

[0052] This embodiment prepares a lithium battery according to Example 1. The difference between this embodiment and Example 1 is that the non-binder polymer C1 used in this embodiment has a D... 50 The thickness is 2.2 μm. Apart from the differences mentioned above, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0053] Example 4

[0054] This embodiment prepares a lithium battery according to Example 1. The difference between this embodiment and Example 1 is that the non-binder polymer C2 used in this embodiment has a D... 50 The thickness is 10 μm. Apart from the differences mentioned above, the materials and processes used in this embodiment are strictly consistent with those in Example 1.

[0055] Example 5

[0056] This embodiment prepares a lithium battery according to Example 1. The difference between this embodiment and Example 1 is that the non-binder polymer C2 used in this embodiment has a D... 50 The thickness is 2.2 μm. Apart from the differences mentioned above, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0057] Example 6

[0058] This example refers to the preparation of lithium battery as in example 1, the difference between this example and example 1 is that in the process of composite separator, the mass ratio of non-binder polymer C1 in the positive electrode side porous active layer is 2% in this example. In addition to the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0059] Example 7

[0060] This example refers to the preparation of lithium battery as in example 1, the difference between this example and example 1 is that in the process of composite separator, the mass ratio of non-binder polymer C1 in the positive electrode side porous active layer is 25% in this example. In addition to the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0061] Example 8

[0062] This example refers to the preparation of lithium battery as in example 1, the difference between this example and example 1 is that in the process of composite separator, the mass ratio of non-binder polymer C2 in the negative electrode side porous active layer is 1% in this example. In addition to the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0063] Example 9

[0064] This example refers to the preparation of lithium battery as in example 1, the difference between this example and example 1 is that in the process of composite separator, the mass ratio of non-binder polymer C2 in the negative electrode side porous active layer is 18% in this example. In addition to the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0065] Example 10

[0066] This example refers to the preparation of lithium battery as in example 1, the difference between this example and example 1 is that the Tg value of non-binder polymer C1 used in this example is 98℃ (non-binder polymer C1 is composed of polymethyl methacrylate, butyl acrylate-styrene copolymer, wherein the molar ratio of polymethyl methacrylate, butyl acrylate-styrene copolymer is 8.4:1.6, and butyl acrylate-styrene copolymer is prepared by butyl acrylate and styrene in a molar ratio of 2.6:7.4). In addition to the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0067] Example 11

[0068] This example is prepared by referring to example 1, and the difference between this example and example 1 is that the Tg value of the non-binder polymer C2 used in this example is 98℃ (the non-binder polymer C2 is composed of polymethyl methacrylate, butyl acrylate-styrene copolymer, wherein the molar ratio of polymethyl methacrylate, butyl acrylate-styrene copolymer is 8.4:1.6, and the butyl acrylate-styrene copolymer is prepared by butyl acrylate and styrene in a molar ratio of 2.6:7.4). Except for the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0069] Example 12

[0070] This example is prepared by referring to example 1, and the difference between this example and example 1 is that the Tg value of the non-binder polymer C2 used in this example is 98℃ (the non-binder polymer C2 is composed of polymethyl methacrylate, butyl acrylate-styrene copolymer, wherein the molar ratio of polymethyl methacrylate, butyl acrylate-styrene copolymer is 8.4:1.6, and the butyl acrylate-styrene copolymer is prepared by butyl acrylate and styrene in a molar ratio of 2.6:7.4). Except for the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0071] Example 13

[0072] This example is prepared by referring to example 1, and the difference between this example and example 1 is that the Tg value of the non-binder polymer C2 used in this example is 98℃ (the non-binder polymer C2 is composed of polymethyl methacrylate, butyl acrylate-styrene copolymer, wherein the molar ratio of polymethyl methacrylate, butyl acrylate-styrene copolymer is 8.4:1.6, and the butyl acrylate-styrene copolymer is prepared by butyl acrylate and styrene in a molar ratio of 2.6:7.4). Except for the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0073] Comparative Example 1

[0074] This example is prepared by referring to example 1, and the difference between this example and example 1 is that the Tg value of the non-binder polymer C2 used in this example is 98℃ (the non-binder polymer C2 is composed of polymethyl methacrylate, butyl acrylate-styrene copolymer, wherein the molar ratio of polymethyl methacrylate, butyl acrylate-styrene copolymer is 8.4:1.6, and the butyl acrylate-styrene copolymer is prepared by butyl acrylate and styrene in a molar ratio of 2.6:7.4). Except for the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0075] Comparative Example 2

[0076] This example is prepared by referring to example 1, and the difference between this example and example 1 is that the Tg value of the non-binder polymer C2 used in this example is 98℃ (the non-binder polymer C2 is composed of polymethyl methacrylate, butyl acrylate-styrene copolymer, wherein the molar ratio of polymethyl methacrylate, butyl acrylate-styrene copolymer is 8.4:1.6, and the butyl acrylate-styrene copolymer is prepared by butyl acrylate and styrene in a molar ratio of 2.6:7.4). Except for the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0077] Comparative Example 3

[0078] This example is prepared by referring to example 1, and the difference between this example and example 1 is that the Tg value of the non-binder polymer C2 used in this example is 98℃ (the non-binder polymer C2 is composed of polymethyl methacrylate, butyl acrylate-styrene copolymer, wherein the molar ratio of polymethyl methacrylate, butyl acrylate-styrene copolymer is 8.4:1.6, and the butyl acrylate-styrene copolymer is prepared by butyl acrylate and styrene in a molar ratio of 2.6:7.4). Except for the above difference, the materials and process operations used in this example are strictly consistent with example 1.

[0079] Comparative Example 4

[0080] The lithium battery of the present comparative example was prepared according to the procedure of Example 1, except that the pressing temperature during the process of compounding the composite separator with the negative electrode sheet was 20°C. Except for the above difference, the materials and process operations used in the present comparative example were strictly the same as those of Example 1.

[0081] Test Example 1

[0082] 1. Test objects:

[0083] Examples 1-13 and Comparative Examples 1-4 were used as the test objects of the present test example.

[0084] 2. Test items:

[0085] (1) Adhesion test between the composite separator and the positive electrode sheet: the tensile machine was used to test the peeling force between the composite separator and the positive electrode sheet.

[0086] (2) Adhesion test between the composite separator and the negative electrode sheet: the tensile machine was used to test the peeling force between the composite separator and the negative electrode sheet.

[0087] (3) High-temperature cycle capacity retention rate of the battery: the battery was subjected to charge and discharge by the new Wei device under the test environment of 45°C; constant current and constant voltage charging was carried out at 1C current to 3.65V, and then the battery was allowed to stand for 10 minutes, followed by constant current discharging at 1C current to 2.5V. The final result was expressed by the capacity retention rate of 1C / 1C cycle charge and discharge for 300 cycles, and the calculation formula was as follows: capacity retention rate (%) = discharge capacity per cycle / first discharge capacity x 100%.

[0088] 3. Test results:

[0089] Table 1 Performance test results of lithium batteries of Examples 1-13 and Comparative Examples 1-4

[0090] Adhesion between composite separator and positive electrode sheet (N / m) Adhesion between composite separator and negative electrode sheet (N / m) High temperature cycle capacity retention rate (%) Example 1 6.8 6.2 95.1 Example 2 5.4 6.1 94.5 Example 3 4.9 6.0 94.3 Example 4 6.6 5.2 94.7 Example 5 6.8 4.8 94.4 Example 6 3.5 6.0 93.2 Example 7 6.8 6.1 95.0 Example 8 6.6 3.2 93.2 Example 9 6.7 6.1 93.4 Example 10 4.3 6.1 93.8 Example 11 6.7 4.2 93.9 Example 12 4.6 6.1 94.0 Example 13 6.6 4.4 94.1 Comparative Example 1 2.1 6.1 91.8 Comparative Example 2 1.7 6.0 91.2 Comparative Example 3 6.7 1.8 91.6 Comparative Example 4 6.6 1.5 90.3

[0091] The test results are shown in Table 1. Comparing the performance test results corresponding to Example 1 and Comparative Example 1, it can be found that the adhesion between the composite separator and the positive electrode sheet prepared in Comparative Example 1 is obviously lower than that of Example 1, and the high temperature cycle capacity retention rate of the battery is obviously lower than that of Example 1. The reason is that under the same conditions of other materials and operations for preparing the battery, the pressing temperature T1 in the compounding process of the positive electrode sheet and the composite separator in Comparative Example 1 is higher than the Tg value (60℃) of the non-adhesive polymer C1, and the raised structure formed by the non-adhesive polymer C1 is prone to deformation, shedding and other adverse problems, and it is difficult to maintain good fit with the positive electrode sheet, thereby the adhesion between the composite separator and the positive electrode sheet and the cycle characteristics of the battery are obviously deteriorated. Comparing the performance test results corresponding to Example 1 and Comparative Example 2, it can be found that the adhesion between the composite separator and the positive electrode sheet prepared in Comparative Example 2 is obviously lower than that of Example 1, and the high temperature cycle capacity retention rate of the battery is obviously lower than that of Example 1. The reason is that under the same conditions of other materials and operations for preparing the battery, the pressing temperature T1 in the compounding process of the positive electrode sheet and the composite separator in Comparative Example 2 is lower than 50℃, and this pressing temperature is difficult to make the raised structure formed by the non-adhesive polymer C1 fully filled in the small pores on the surface of the positive electrode sheet, thereby the adhesion between the composite separator and the positive electrode sheet and the cycle characteristics of the battery are obviously deteriorated.

[0092] Comparing the performance test results of Example 1 and Comparative Example 3, it can be found that the adhesion between the composite separator prepared by Comparative Example 2 and the negative electrode sheet is obviously lower than that of Example 1, and the high-temperature cycle capacity retention rate of the battery is obviously lower than that of Example 1. The reason is that under the same conditions of other materials and operations for preparing the battery, the pressing temperature T2 in the compounding process of the negative electrode sheet and the composite separator of Comparative Example 3 is higher than the Tg value (40℃) of the non-adhesive polymer C2, and the raised structure formed by the non-adhesive polymer C2 is prone to deformation, shedding and other adverse problems, and it is difficult to maintain good fit with the negative electrode sheet, thereby the adhesion between the composite separator and the negative electrode sheet and the cycle performance of the battery are obviously deteriorated. Comparing the performance test results of Example 1 and Comparative Example 4, it can be found that the adhesion between the composite separator prepared by Comparative Example 4 and the negative electrode sheet is obviously lower than that of Example 1, and the high-temperature cycle capacity retention rate of the battery is obviously lower than that of Example 1. The reason is that under the same conditions of other materials and operations for preparing the battery, the pressing temperature T2 in the compounding process of the negative electrode sheet and the composite separator of Comparative Example 4 is lower than 28℃, and this pressing temperature is difficult to make the raised structure formed by the non-adhesive polymer C2 fully filled in the small pores on the surface of the negative electrode sheet, thereby the adhesion between the composite separator and the negative electrode sheet and the cycle performance of the battery are obviously deteriorated.

[0093] Comparing the performance test results of Example 1 and Examples 2-3. As shown in Table 1, under the same conditions of other materials and operations for preparing the battery, the D 50 The ratio of the thickness of the first base coating layer to the thickness of the first base coating layer is greater than 4:1, and the D 50 The ratio of the thickness of the first base coating layer to the thickness of the first base coating layer is less than 1.3:1, and the adhesion between the composite separator obtained thereby and the positive electrode sheet is lower than that of Example 1, and the high-temperature cycle capacity retention rate of the battery is lower than that of Example 1. Therefore, compared with Examples 2 and 3, Example 1 further reasonably sets the D 50 The ratio of the thickness of the first base coating layer to the thickness of the first base coating layer is greater than 4:1, and the D

[0094] Comparing the performance test results of Example 1 and Examples 4-5. As shown in Table 1, under the same conditions of other materials and operations for preparing the battery, the D 50 The ratio of the thickness of the first base coating layer to the thickness of the first base coating layer is greater than 4:1, and the D 50The ratio of the thickness of the second base coating layer is <1.3:1, and the adhesion between the composite separator and the negative electrode sheet is lower than that of Example 1, and the high-temperature cycle capacity retention of the battery is lower than that of Example 1. Therefore, it is shown that, compared with Examples 4 and 5, Example 1 further reasonably sets the D 50 The ratio of the thickness of the second base coating layer is <1.3:1, and the adhesion between the composite separator and the negative electrode sheet is lower than that of Example 1, and the high-temperature cycle capacity retention of the battery is lower than that of Example 1. Therefore, it is shown that, compared with Examples 4 and 5, Example 1 further reasonably sets the D

[0095] The performance test results of Example 1 and Example 6 are compared. As shown in Table 1, under the same conditions of other materials and operations for preparing the battery, the content of the non-binder polymer C1 in the first coating slurry for forming the positive electrode side porous active layer of the composite separator in Example 6 is less, and the adhesion between the composite separator and the positive electrode sheet is lower than that of Example 1, and the high-temperature cycle capacity retention of the battery is lower than that of Example 1. Therefore, it is shown that, compared with Example 6, Example 1 effectively controls the content of the non-binder polymer C1 in the positive electrode side porous active layer, so that the surface of the composite separator has a sufficient amount of protruding structures, and the probability of the non-binder polymer C1 embedding into the first positive electrode active coating layer of the positive electrode sheet is effectively increased, thereby improving the adhesion effect and the fit between the composite separator and the positive electrode sheet; and the high Tg value non-binder polymer C1 with the above content can effectively ensure the heat shrinkage performance and the air permeability of the separator, thereby further improving the cycle characteristics of the lithium battery.

[0096] The performance test results of Example 1 and Examples 8 and 9 are compared. As shown in Table 1, under the same conditions of other materials and operations for preparing the battery, the content of the non-binder polymer C2 in the second coating slurry for forming the negative electrode side porous active layer of the composite separator in Example 8 is less, and the content of the non-binder polymer C2 in the second coating slurry for forming the negative electrode side porous active layer of the composite separator in Example 9 is more, and the adhesion between the composite separator and the negative electrode sheet is lower than that of Example 1, and the high-temperature cycle capacity retention of the battery is lower than that of Example 1. Therefore, it is shown that, compared with Examples 8 and 9, Example 1 effectively controls the content of the non-binder polymer C2 in the negative electrode side porous active layer, and the low Tg value non-binder polymer C2 with the appropriate content can not only ensure the excellent heat shrinkage performance of the composite separator, but also ensure that the surface of the composite separator has a suitable amount of protruding structures, so that the fit between the composite separator and the negative electrode sheet is maintained at a high level, thereby improving the adhesion effect and the fit between the composite separator and the negative electrode sheet, and further improving the cycle characteristics of the lithium battery.

[0097] Comparing the performance test results of Example 1 and Example 10, it can be found that the adhesion between the composite separator and the positive electrode sheet prepared in Example 10 is lower than that in Example 1, and the high-temperature cycle capacity retention of the battery prepared in Example 10 is lower than that in Example 1. The reason is that, under the same conditions of other materials and operations for preparing the battery, the non-adhesive polymer C1 with a Tg value higher than 90℃ is used in Example 10, and the non-adhesive polymer C1 has poor elasticity, which is difficult to fill in the small pores of the positive electrode sheet in the compounding process (the compaction temperature T1 is 52℃) of the positive electrode sheet and the composite separator, thereby reducing the adhesion between the composite separator and the positive electrode sheet and the cycle performance of the battery. Comparing the performance test results of Example 1 and Example 11, it can be found that the adhesion between the composite separator and the negative electrode sheet prepared in Example 11 is lower than that in Example 1, and the high-temperature cycle capacity retention of the battery prepared in Example 11 is lower than that in Example 1. The reason is that, under the same conditions of other materials and operations for preparing the battery, the non-adhesive polymer C2 with a Tg value higher than 90℃ is used in Example 11, and the non-adhesive polymer C2 has insufficient elasticity to fill in the pores of the negative electrode sheet in the compounding process (the compaction temperature T2 is 30℃) of the negative electrode sheet and the composite separator, thereby reducing the adhesion between the composite separator and the negative electrode sheet and the cycle performance of the battery.

Claims

1. An electric cell, comprising a positive electrode sheet, a composite separator and a negative electrode sheet arranged in sequence; the positive electrode sheet comprises a positive electrode current collector and a first positive electrode active coating layer, the first positive electrode active coating layer is arranged on the surface of the positive electrode current collector facing the composite separator; the negative electrode sheet comprises a negative electrode current collector and a first negative electrode active coating layer, the first negative electrode active coating layer is arranged on the surface of the negative electrode current collector facing the composite separator; the composite separator comprises a porous substrate layer, a positive electrode side porous active layer and a negative electrode side porous active layer, the surface of the porous substrate layer facing the positive electrode sheet is a first surface, the positive electrode side porous active layer is arranged on the first surface, the surface of the porous substrate layer facing the negative electrode sheet is a second surface, and the negative electrode side porous active layer is arranged on the second surface; The positive electrode-side porous active layer includes a first base coating layer and a non-binder polymer C1 embedded in the first base coating layer, the non-binder polymer C1 having a D 50 > thickness of the first base coating layer; the negative electrode-side porous active layer includes a second base coating layer and a non-binder polymer C2 embedded in the second base coating layer, the non-binder polymer C2 having a D 50 > thickness of the second base coating layer; The compacted density of the first positive electrode active coating is 2.05-3.60 g / cm 3 ; The compacted density of the first negative electrode active coating is 1.40-1.85 g / cm 3 ; the composite of the positive electrode sheet and the composite separator is realized by a pressing treatment I, the pressing temperature T1 of the pressing treatment I satisfies 50℃≤T1<Tg value of the non-binder polymer C1, and the pressing pressure of the pressing treatment I is not less than 0.2 tons; the composite of the negative electrode sheet and the composite separator is realized by a pressing treatment II, the pressing temperature T2 of the pressing treatment II satisfies 28℃≤T2<Tg value of the non-binder polymer C2, and the pressing pressure of the pressing treatment II is not less than 0.2 tons.

2. The cell of claim 1, wherein, D of the non-adhesive polymer C1 50 : the thickness of the first base coating = (1.3~4):

1.

3. The cell of claim 1, wherein, D of the non-adhesive polymer C2 50 : the thickness of the second base coating = (1.3~4):

1.

4. The cell of claim 1, wherein, The mass percentage of the non-binder polymer C1 in the positive electrode side porous active layer is 3%-22%.

5. The cell of claim 1, wherein, The mass percentage of the non-binder polymer C2 in the negative electrode side porous active layer is 2%-17%.

6. The cell of claim 1, wherein, The Tg value of the non-binder polymer C1 is 55-90℃.

7. The cell of claim 1, wherein, The Tg value of the non-binder polymer C2 is 30-90℃. 8.The electric cell of claim 1, wherein the pressing temperature T1 of the pressing treatment I is 50-70℃, and the pressing pressure of the pressing treatment I is 0.2-14 tons; the pressing temperature T2 of the pressing treatment II is 28-48℃, and the pressing pressure of the pressing treatment II is 0.2-14 tons.

9. The cell of any one of claims 1 to 8, wherein, The first positive electrode active coating includes a first positive electrode active material, and the first positive electrode active material has a D 50 The thickness is 0.1~20μm; the first negative electrode active coating includes a first negative electrode active material, and the D of the first negative electrode active material is... 50 The value is 5~20μm. 10.A lithium battery comprising the electric cell of any one of claims 1-9.