Secondary battery and electric device

Abstract

The invention relates to a secondary battery and an electric device, and belongs to the technical field of batteries. The secondary battery comprises a positive pole piece, a composite diaphragm and a negative pole piece, the composite diaphragm comprises a diaphragm base body, a first elastic coating which is arranged on the surface of one side of the diaphragm base body and is in contact with the negative pole piece, and a second elastic coating which is arranged on the surface of the other side of the diaphragm base body and is in contact with the positive pole piece; the secondary battery satisfies the following conditions: Ra > Rc; wherein Ra represents the elastic recovery rate of the first elastic coating after the pressure intensity of 15 MPa is applied; and Rc represents the elastic recovery rate of the second elastic coating after the pressure intensity of 15 MPa is applied. The secondary battery can effectively reduce the influence of volume change of the pole piece in the charging and discharging process, so that the service life of the battery is prolonged, and the safety performance of the battery is improved.

Description

Technical Field

[0001] This application belongs to the technical field of batteries, and particularly relates to a secondary battery and an electrical device. Background Art

[0002] During the charge and discharge process of a lithium-ion battery, due to the insertion and extraction of lithium ions, the electrode sheet will undergo periodic volume expansion and contraction. This volume change will exert pressure on the internal structure of the battery, especially on the separator, thereby affecting the cycle performance and safety performance of the battery. Currently, the commonly used separators are mostly polymer films with a porous structure. Although such separators have certain mechanical strength and electrochemical stability, it is still difficult to effectively buffer the extrusion of the separator caused by the volume change of the electrode sheet during the charge and discharge process of the battery, resulting in poor battery performance. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery and an electrical device by overcoming the deficiencies of the prior art.

[0004] To achieve the above purpose, the technical solution adopted in this application is as follows:

[0005] In the first aspect, this application provides a secondary battery, which includes a positive electrode sheet, a composite separator, and a negative electrode sheet;

[0006] The composite separator includes a separator matrix, a first elastic coating disposed on one surface of the separator matrix and in contact with the negative electrode sheet, and a second elastic coating disposed on the other surface of the separator matrix and in contact with the positive electrode sheet;

[0007] The secondary battery satisfies: Ra > Rc;

[0008] Wherein, Ra represents the elastic recovery rate of the first elastic coating after applying a pressure of 15 MPa; Rc represents the elastic recovery rate of the second elastic coating after applying a pressure of 15 MPa.

[0009] As an embodiment of this application, the first elastic coating includes a first core-shell structured polymer; the first core-shell structured polymer includes a core layer and a shell layer, the core layer includes at least one of polyurethane and biobased polycarbonate, and the shell layer includes at least one of polyether and crosslinked polyvinyl alcohol;

[0010] The second elastic coating includes a second core-shell structured polymer; the second core-shell structured polymer includes an inner core and an outer shell, the inner core includes at least one of polystyrene and biobased polycarbonate, and the outer shell includes at least one of crosslinked polyvinyl alcohol and methyl methacrylate-methylacrylic acid copolymer.

[0011] As an embodiment of the present application, the particle size D of the first core-shell structured polymer v50 is 1 to 5 μm, and the particle size D of the second core-shell structured polymer v50 is 0.1 to 1 μm.

[0012] As an embodiment of the present application, the mass ratio of the first core-shell structured polymer in the first elastic coating is 90% to 98%; the mass ratio of the second core-shell structured polymer in the second elastic coating is 80% to 90%.

[0013] As an embodiment of the present application, the thickness of the first elastic coating is 0.2 to 5 μm, and the thickness of the second elastic coating is 0.2 to 5 μm.

[0014] As an embodiment of the present application, the porosity of the first elastic coating is 30% to 50%, and the porosity of the second elastic coating is 50% to 80%.

[0015] As an embodiment of the present application, the first elastic coating and / or the second elastic coating further includes a ceramic material, and the ceramic material includes at least one of Al2O3, AlOOH, Mg(OH)2, SiO2, MgO, CaO, Cr2O3.

[0016] As an embodiment of the present application, the particle size D of the ceramic material v50 is 0.5 to 4 μm.

[0017] As an embodiment of the present application, the mass ratio of the ceramic material in the first elastic coating or in the second elastic coating is 1% to 10%.

[0018] As an embodiment of the present application, the separator substrate includes a polyolefin and an additive, and the additive includes at least one of ethylene-octene copolymer (POE), ethylene propylene diene monomer rubber, and polyisoprene rubber. The mass ratio of the additive in the separator substrate is 5% to 20%.

[0019] In a second aspect, the present application provides an electrical device, including the above secondary battery, and the secondary battery serves as a power supply of the electrical device.

[0020] Compared with the prior art, the beneficial effects of the present application are:

[0021] In the present application, a composite separator is formed by respectively disposing a first elastic coating and a second elastic coating on both sides of a separator substrate. The first elastic coating is in contact with the negative electrode sheet, and the second elastic coating is in contact with the positive electrode sheet, so that the composite separator can be adaptively compressed and rebound during the charge and discharge process of the battery, thereby effectively absorbing the stress generated by the volume change of the positive or negative electrode material, reducing the oppression of the electrode sheet on the separator, maintaining the stability of the internal structure of the battery, and further improving the cycle life and safety of the battery. Detailed Embodiments

[0022] In order to better illustrate the purpose, technical solutions and advantages of the present application, the present application will be further described below in conjunction with specific embodiments and comparative examples. The purpose is to understand the content of the present application in detail, rather than a limitation of the present application. All other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application. The experimental reagents and instruments involved in the implementation of the present application are all common ordinary reagents and instruments unless otherwise specified.

[0023] According to a first aspect of the present application, a secondary battery is provided. The secondary battery includes a positive electrode sheet, a composite separator and a negative electrode sheet;

[0024] The composite separator includes a separator substrate, a first elastic coating disposed on one surface of the separator substrate and in contact with the negative electrode sheet, and a second elastic coating disposed on the other surface of the separator substrate and in contact with the positive electrode sheet;

[0025] The secondary battery satisfies: Ra > Rc;

[0026] Wherein, Ra represents the elastic recovery rate of the first elastic coating after applying a pressure of 15 MPa; Rc represents the elastic recovery rate of the second elastic coating after applying a pressure of 15 MPa.

[0027] In the present application, a composite separator is formed by respectively disposing a first elastic coating and a second elastic coating on both sides of a separator substrate. The first elastic coating is in contact with the negative electrode sheet, and the second elastic coating is in contact with the positive electrode sheet, so that the composite separator can be adaptively compressed and rebound during the charge and discharge process of the battery, thereby effectively absorbing the stress generated by the volume change of the positive or negative electrode, reducing the oppression of the electrode sheet on the separator, maintaining the stability of the internal structure of the battery, and further improving the cycle life and safety of the battery.

[0028] Meanwhile, although both the positive and negative electrode materials will undergo structural changes during the lithium deintercalation and intercalation processes, the degrees of swelling caused by the two are different, resulting in a higher degree of swelling of the negative electrode sheet than that of the positive electrode sheet. Contacting the negative electrode sheet with the first elastic coating having a higher elastic recovery rate can correspondingly undergo elastic deformation when the negative electrode sheet expands and contracts, which can not only effectively reduce the extrusion of the negative electrode sheet on the separator, but also closely adhere to the negative electrode sheet during the entire volume change process; while contacting the positive electrode sheet with the second elastic coating having a lower elastic recovery rate can better match the volume change of the positive electrode sheet, thereby reducing the internal pressure of the battery and enhancing the stability of the internal structure of the battery.

[0029] Optionally, Ra≥90%, preferably 98%≥Ra≥90%, specifically any one or the range value of any two of 98%, 97%, 96%, 95%, 94%, 93%, 92%, 91%, 90%; 89%≥Rc≥80%, specifically any one or the range value of any two of 89%, 88%, 87%, 86%, 85%, 84%, 83%, 82%, 81%, 80%. When Ra and Rc are within the above ranges, the volume changes of the positive electrode sheet and the negative electrode sheet can be further matched, the stability of the internal structure of the battery can be enhanced, and the electrochemical performance of the battery can be improved.

[0030] The specific calculation formulas of Ra and Rc are as follows:

[0031] Ra = (L2 - L1) / (L0 - L2);

[0032] L0 μm is the thickness of the first elastic coating;

[0033] L1 μm is the thickness of the first elastic coating when a pressure of 15 MPa is applied;

[0034] L2 μm is the thickness of the first elastic coating after the application of 15 MPa pressure is released.

[0035] Rc = (h2 - h1) / (h0 - h2);

[0036] h0 μm is the thickness of the second elastic coating;

[0037] h1 μm is the thickness of the second elastic coating when a pressure of 15 MPa is applied;

[0038] h2 μm is the thickness of the second elastic coating after the application of 15 MPa pressure is released.

[0039] Optionally, the above-mentioned negative electrode sheet can be a lithium metal negative electrode sheet, or include a current collector and a negative electrode material layer provided on at least one surface of the current collector. The negative electrode material layer contains a negative electrode active material, and the negative electrode active material includes any one of graphite, hard carbon, silicon carbide, and silicon oxide.

[0040] The positive electrode sheet of the present application includes a current collector and a positive electrode material layer provided on at least one surface of the current collector. The positive electrode material layer contains a positive electrode active material, and the positive electrode active material includes any one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, and lithium manganese iron phosphate.

[0041] In some embodiments, the first elastic coating includes a first core-shell structured polymer; the first core-shell structured polymer includes a core layer and a shell layer. The core layer includes at least one of polyurethane and bio-based polycarbonate, and the shell layer includes at least one of polyether and crosslinked polyvinyl alcohol.

[0042] The second elastic coating includes a second core-shell structured polymer; the second core-shell structured polymer includes an inner core and an outer shell. The inner core includes at least one of polystyrene and bio-based polycarbonate, and the outer shell includes at least one of crosslinked polyvinyl alcohol and methyl methacrylate-methyl acrylic acid copolymer.

[0043] It is found that the core layer of the above-mentioned first core-shell structured polymer or the inner core of the second core-shell structured polymer has high elasticity and low hardness, and can provide good deformation recovery ability; while the shell layer of the first core-shell structured polymer or the outer shell of the second core-shell structured polymer has high hardness and certain rigidity, which can not only enhance the stability between particles, but also prevent adhesion between particles, so that the first elastic coating and the second elastic coating have excellent elastic recovery performance.

[0044] In some embodiments, the particle size D of the first core-shell structured polymer v50 is 1-5 μm, and the particle size D of the second core-shell structured polymer v50 is 0.1-1 μm.

[0045] Optionally, the particle size D of the first core-shell structured polymer v50 can specifically be any one or the range value of any two of 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm; the particle size D of the second core-shell structured polymer v50 can specifically be any one or the range value of any two of 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm. It is found that the first core-shell structured polymer (particle size D v50(with a particle size of 1 - 5 μm). A larger particle size helps to form a tougher elastic network structure, which can better adapt to the large volume expansion and contraction of the negative electrode during charge and discharge, ensuring that the first elastic coating still maintains a high elastic recovery rate (Ra) under high pressure (such as 15 MPa), thereby effectively buffering the mechanical stress of the negative electrode volume change on the separator and maintaining stable contact at the electrode interface.

[0046] The second core - shell structure polymer (particle size D v50 is 0.1 - 1 μm). A smaller particle size can make the coating denser and more uniform, which can not only meet the elastic requirements of the relatively small volume change on the positive electrode side (Rc is relatively low), but also optimize the ion transport path through a finer structure and improve the ion conduction efficiency of the coating.

[0047] The large particle size on the negative electrode side provides strong anti - deformation ability, and the small particle size on the positive electrode side ensures conduction stability, forming a "high - elasticity buffering - stable conduction" synergistic effect. While satisfying Ra > Rc, it balances the interface pressure, reduces the relative displacement and impedance growth between the electrode and the separator, extends the battery life and improves safety.

[0048] In some embodiments, the mass ratio of the first core - shell structure polymer in the first elastic coating is 90% - 98%; the mass ratio of the second core - shell structure polymer in the second elastic coating is 80% - 90%.

[0049] Optionally, the mass ratio of the first core - shell structure polymer in the first elastic coating can specifically be any one or the range value of any two of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%; the mass ratio of the second core - shell structure polymer in the second elastic coating can specifically be any one or the range value of any two of 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%. It is found that for the first elastic coating (negative electrode side, 90% - 98%), a high proportion of elastic materials forms a tough coating, adapts to the large volume expansion of the negative electrode during charge and discharge, maintains high elastic recovery under high pressure, reduces the risk of separator rupture, and stabilizes electrode contact.

[0050] The second elastic coating (positive electrode side, 80% - 90%), a moderate proportion not only meets the elastic requirements of the relatively small volume change of the positive electrode, but also leaves space for adding functional materials such as ceramics, improves the heat resistance and ion conduction efficiency of the coating, and adapts to the high - voltage environment of the positive electrode.

[0051] The difference in the proportion of the positive and negative electrode coating materials can accurately match the volume change amplitudes of the two electrodes, achieve "strong buffering on the negative electrode and stable conduction on the positive electrode", reduce the growth of interface impedance, extend the battery life and improve safety.

[0052] In some embodiments, the thickness of the first elastic coating is 0.2 - 5 μm, and the thickness of the second elastic coating is 0.2 - 5 μm.

[0053] Optionally, the thickness of the first elastic coating may specifically be any one of 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or the range value of any two of them; the thickness of the second elastic coating may specifically be any one of 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or the range value of any two of them. It has been found that the combination of the first elastic coating and the second elastic coating within the above thickness range is more beneficial to improving the mechanical properties and electrochemical stability of the separator.

[0054] In some embodiments, the porosity of the first elastic coating is 30% - 50%, and the porosity of the second elastic coating is 50% - 80%.

[0055] Optionally, the porosity of the first elastic coating may specifically be any one of 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50% or the range value of any two of them; the porosity of the second elastic coating may specifically be any one of 50%, 53%, 55%, 58%, 60%, 63%, 65%, 67%, 70%, 73%, 75%, 78%, 80% or the range value of any two of them. It has been found that the negative electrode side coating (30% - 50% low porosity) has a denser structure and stronger elasticity, which can effectively buffer the large volume expansion during the charge and discharge of the negative electrode (such as the expansion of the silicon-based negative electrode), reduce the coating rupture or separation from the electrode, and stabilize the interfacial contact.

[0056] The positive electrode side coating (50% - 80% high porosity) has many pores, fast ion transport, good electrolyte wettability, improves the conduction efficiency, and at the same time adapts to the small volume change of the positive electrode to avoid an increase in internal resistance or mechanical embrittlement.

[0057] The difference in porosity between the two electrodes matches their respective requirements (strong buffering for the negative electrode and excellent conduction for the positive electrode), reduces the growth of internal resistance and contact failure, prolongs the battery life and improves safety.

[0058] In some embodiments, the first elastic coating and / or the second elastic coating further includes a ceramic material, and the ceramic material includes at least one of Al2O3, AlOOH, Mg(OH)2, SiO2, MgO, CaO, Cr2O3. The ceramic material is beneficial to improving the mechanical strength and thermal stability of the composite separator.

[0059] In some embodiments, the particle size D of the ceramic material v50 is 0.5 - 4 μm.

[0060] Optionally, the particle size D of the ceramic material v50 can specifically be any one or the range value of any two of 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm. It has been found that when the particle size D of the ceramic material v50 is within the above range, the thermal stability and mechanical strength of the ceramic coating on the separator can be effectively exerted, and at the same time, the uniformity of the coating slurry can be improved, and the coating thickness is easier to control.

[0061] In some embodiments, the mass proportion of the ceramic material in the first elastic coating or in the second elastic coating is 1% - 10%.

[0062] Optionally, the mass proportion of the ceramic material in the first elastic coating or in the second elastic coating can specifically be any one or the range value of any two of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%. When the mass proportion of the ceramic material is within the above range, the heat resistance and mechanical strength of the separator can be effectively improved, and the embrittlement and cracking of the coating can be reduced.

[0063] In some embodiments, the separator substrate includes polyolefin and additives, the additives include at least one of ethylene-octene copolymer (POE), ethylene propylene diene monomer rubber, and polyisoprene rubber, and the mass proportion of the additives in the separator substrate is 5% - 20%. It has been found that when the separator substrate contains the above additives, not only can the mechanical strength and flexibility of the separator substrate be improved to enhance the puncture resistance and tensile resistance of the separator substrate, but also it is beneficial to improve the thermal stability of the separator substrate, and at the same time, it can also improve the dispersion uniformity of the electrolyte in the separator substrate to improve its ion conduction ability.

[0064] Optionally, the mass proportion of the additives in the separator substrate can specifically be any one or the range value of any two of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%. When the separator substrate contains the above additives, it can have better elasticity.

[0065] In some embodiments, the thickness of the separator substrate is 2 to 30 μm. Optionally, the thickness of the separator substrate may specifically be any one of 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm or the range value of any two of them. It has been found that when the thickness of the separator substrate in the composite separator is within the above range, it can not only maintain a high ion transport efficiency to reduce the internal resistance of the battery, but also maintain good mechanical strength to improve the safety performance of the battery.

[0066] In some embodiments, the porosity of the separator substrate is 20% to 70%. Optionally, the porosity of the separator substrate may specifically be any one of 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or the range value of any two of them. It has been found that when the porosity of the separator substrate is within the above range, it can have better thermal stability while having high electrolyte permeability, thereby improving the charge and discharge efficiency and cycle stability of the battery.

[0067] In a second aspect, the present application provides an electrical device, including the above secondary battery, and the secondary battery serves as the power supply of the electrical device.

[0068] To clearly understand the technical solution of the present application, the following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0069] 1) The first core-shell structured polymer is prepared by the following preparation method:

[0070] S1. Dissolve the modified polyurethane prepolymer (Wanhua Chemical MDI-100) in N,N-dimethylformamide (DMF) to form a uniform solution; then, add a stabilizer (antioxidant 1010) under stirring and continue stirring until it is completely dissolved to obtain a core material solution;

[0071] S2. Dissolve the heat-resistant polyether (Evonik Degussa VESTAKEEP 2000CF30) in N,N-dimethylformamide (DMF) to form a uniform solution, and then add an initiator (dicumyl peroxide) thereto and stir evenly to obtain a shell material solution;

[0072] S3. Slowly drop the core material solution in S1 into the shell material solution in S2 according to the mass ratio of the core material to the shell material of 6:4, and stir at a constant temperature to form a stable emulsion; after the reaction is completed, obtain the first core-shell structured polymer through precipitation, filtration, washing, and drying.

[0073] 2) The second core-shell structured polymer A is prepared by the following preparation method:

[0074] S1. Disperse functional polystyrene microspheres (amino-modified polystyrene microspheres from Sigma-Aldrich with an average particle size of 1 μm) in deionized water to form a uniform suspension, obtaining a core material solution;

[0075] S2. Dissolve polyvinyl alcohol in deionized water to form a transparent solution, then add a cross-linking agent (glutaraldehyde) thereto and stir evenly to obtain a shell material solution;

[0076] S3. Slowly drop the core material solution in S1 into the shell material solution in S2 according to a mass ratio of core material to shell material of 6:4, and stir at a constant temperature to form a stable emulsion; after the reaction is completed, obtain the second core-shell structured polymer A through precipitation, filtration, washing, and drying.

[0077] 3) The second core-shell structured polymer B is prepared by the following preparation method:

[0078] S1. Dissolve bio-based polycarbonate (Bio-PC) in N,N-dimethylformamide (DMF) to form a uniform suspension, obtaining a core material solution;

[0079] S2. Dissolve methyl methacrylate copolymer (MMA-co-MAA) in N,N-dimethylformamide (DMF) to form a transparent solution, then add a cross-linking agent (benzoyl peroxide) and an initiator (azobisisobutyronitrile) thereto and stir evenly to obtain a shell material solution;

[0080] S3. Slowly drop the core material solution in S1 into the shell material solution in S2 according to a mass ratio of core material to shell material of 6:4, and stir at a constant temperature to form a stable emulsion; after the reaction is completed, obtain the second core-shell structured polymer B through precipitation, filtration, washing, and drying.

[0081] Example 1

[0082] This example provides a secondary battery, and its preparation method includes the following steps:

[0083] Stack the positive electrode sheet, the composite separator, and the negative electrode sheet in sequence, with the composite separator in the middle of the positive and negative electrode sheets (the first elastic coating in the composite separator contacts the negative electrode sheet, and the second elastic coating contacts the positive electrode sheet), wind it to form an inner core, perform hot pressing and shaping, and weld the tabs to obtain a bare battery cell; then place the bare battery cell in an outer packaging aluminum-plastic film and bake it in an oven, inject the electrolyte into the dried battery, and let it stand, age, and grade-capacity test to obtain the secondary battery.

[0084] 1) The preparation method of the above composite separator includes the following steps:

[0085] S1. Dissolve the core-shell structure polymer (the first core-shell structure polymer) in N,N-dimethylformamide (DMF) to form a uniform solution, then add the ceramic material (AlOOH) thereto, and stir evenly to obtain coating slurry 1;

[0086] Dissolve the core-shell structure polymer (the second core-shell structure polymer A) in N,N-dimethylformamide (DMF) to form a uniform solution, then add the ceramic material (AlOOH) thereto, and stir evenly to obtain coating slurry 2;

[0087] S2. Coating slurry 1 in S1 is coated on one side surface of the separator substrate (PP separator), and dried to obtain the first elastic coating; coating slurry 2 in S1 is coated on the other side surface of the separator substrate (PP separator), and dried to obtain the second elastic coating.

[0088] 2) The preparation method of the above positive electrode sheet includes the following steps:

[0089] Mix the positive active material NCM622, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 96.5:2:1.5, mix the slurry with N-methylpyrrolidone as the solvent, and then coat it on the aluminum foil. After drying, rolling, slitting, and cutting, the positive electrode sheet is obtained;

[0090] 3) The preparation method of the above negative electrode sheet includes the following steps:

[0091] Mix the negative electrode material (composed of graphite and silicon carbide in a mass ratio of 92:8), conductive agent SP, binder styrene-butadiene rubber (SBCs), and thickener carboxymethyl cellulose (CMC) in a weight ratio of 94:1.5:3.5:1, add them to deionized water, and stir well to obtain the negative electrode slurry. Then coat the negative electrode slurry on the copper foil, dry, roll, and slit to obtain the negative electrode sheet.

[0092] 4) The above electrolyte is a 1 mol / L lithium hexafluorophosphate solution, and the solvent thereof is composed of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1.

[0093] Example 2

[0094] Example 2 provides a secondary battery. The difference between this secondary battery and Example 1 is that the core-shell structure polymer in the second elastic coating of the composite separator is the second core-shell structure polymer B.

[0095] Examples 3 and 4

[0096] Examples 3 and 4 provide a secondary battery. The difference between this secondary battery and Example 2 is that the particle size D of the core-shell structure polymer in the first elastic coating of the composite separator v50 is different, and the particle size D of the core-shell structure polymer in the second elastic coatingv50 Different

[0097] Examples 5 and 6

[0098] Examples 5 and 6 provide a secondary battery, which is different from Example 2 in that the mass ratio of the core-shell structure polymer in the first elastic coating of the composite separator is different, and the mass ratio of the core-shell structure polymer in the second elastic coating is different.

[0099] Examples 7 and 8

[0100] Examples 7 and 8 provide a secondary battery, which is different from Example 2 in that the thickness of the first elastic coating in the composite separator is different, and the thickness of the second elastic coating is different.

[0101] Examples 9 and 10

[0102] Examples 9 and 10 provide a secondary battery, which is different from Example 2 in that the porosity of the first elastic coating in the composite separator is different, and the porosity of the second elastic coating is different.

[0103] Examples 11 and 12

[0104] Examples 11 and 12 provide a secondary battery, which is different from Example 2 in that the types of ceramic materials in the first elastic coating of the composite separator are different, and the types of ceramic materials in the second elastic coating are different.

[0105] Examples 13 and 14

[0106] Examples 13 and 14 provide a secondary battery, which is different from Example 2 in that the particle size D of the ceramic material in the first elastic coating of the composite separator v50 is different, and the particle size D of the ceramic material in the second elastic coating v50 is different.

[0107] Examples 15 and 16

[0108] Examples 15 and 16 provide a secondary battery, which is different from Example 2 in that the mass ratio of the ceramic material in the first elastic coating of the composite separator is different, and the mass ratio of the ceramic material in the second elastic coating is different.

[0109] Comparative Examples 1 and 2

[0110] Comparative Examples 1 and 2 provide a secondary battery, which is different from Example 2 in that the types of core-shell structure polymers in the first elastic coating of the composite separator are different, and the types of core-shell structure polymers in the second elastic coating are different.

[0111] Table 1 The first elastic coating in the composite separator of the secondary batteries of each example and comparative example

[0112]

[0113]

[0114] In Table 1, Ra is the elastic recovery rate of the first elastic coating after applying a pressure of 15 MPa;

[0115] Ra = (L2 - L1) / (L0 - L2);

[0116] L0 μm is the thickness of the first elastic coating;

[0117] L1 μm is the thickness of the first elastic coating when applying a pressure of 15 MPa;

[0118] L2 μm is the thickness of the first elastic coating after releasing the pressure of 15 MPa.

[0119] The specific test method of Ra is as follows:

[0120] For the separators corresponding to each example and comparative example in Table 1, the cross-section of the separator is obtained by argon ion polishing, and the thickness of each layer (substrate, first elastic coating, second elastic coating) is measured by SEM; the first and second elastic coatings are distinguished by infrared testing (characteristic peaks) to obtain the thickness L0 of the first elastic coating; the first and second elastic coatings are removed by mechanical peeling method, and then a pressure of 15 MPa is applied to the substrate by a TMA instrument (i.e., a thermomechanical analysis instrument), and the force is removed, and the equipment records the thicknesses at the time of applying the force and after removing the force, L1 基体 、L2 基体 ; the second elastic coating is removed by mechanical peeling method, and then a pressure of 15 MPa is applied to the substrate / first elastic coating by a TMA instrument, and the force is removed, and the equipment records the thicknesses before applying the force, at the time of applying the force, and after removing the force, and L1 基体第一弹性涂层 、L2 基体第一弹性涂层 are obtained respectively, where L1 = L1 基体第一弹性涂层 -L1 基体 , L2 = L2 基体第一弹性涂层 -L2 基体 .

[0121] Table 2 The second elastic coating in the composite separator of the secondary batteries of each example and comparative example

[0122]

[0123] In Table 2, Rc is the elastic recovery rate of the second elastic coating after applying a pressure of 15 MPa;

[0124] Rc = (h2 - h1) / (h0 - h2);

[0125] h0 μm is the thickness of the second elastic coating;

[0126] h1 μm is the thickness of the second elastic coating when a pressure of 15 MPa is applied;

[0127] h2 μm is the thickness of the second elastic coating after the pressure of 15 MPa is released.

[0128] The specific test method of Rc is as follows:

[0129] For the diaphragms corresponding to each example and comparative example in Table 2, the cross-section of the diaphragm is obtained by argon ion polishing, and the thickness of each layer (substrate, first elastic coating, second elastic coating) is measured by SEM; the first and second elastic coatings are distinguished by infrared testing (characteristic peaks) to obtain the thickness h0 of the second elastic coating; the first elastic coating is removed by mechanical peeling method, and then a pressure of 15 MPa is applied to the substrate / second elastic coating by a TMA instrument, and the force is removed. The equipment records the thickness when the force is applied and after the force is removed, and h1 基体 / 第二弹性涂层 , h2 基体 / 第二弹性涂层 , where h1 = h1 基体 / 第二弹性涂层 -L1 基体 , h2 = h2 基体第二弹性涂层 -h2 基体 .

[0130] Performance test

[0131] 1) Volume expansion rate after 2000 cycles

[0132] The secondary batteries in each example and comparative example are subjected to charge and discharge tests at 25 °C in the voltage range of 2.8 - 4.25 V at 1C / 1C. After the SOC is charged from 0% to 100% and then discharged to 0%, it is regarded as one charge and discharge cycle, and this is repeated 2000 times; the volume is measured by the drainage method, and the initial volume V1 of the secondary battery is recorded. After the battery is cycled 2000 times, the volume V2 of the expanded secondary battery is measured again by the drainage method. The volume expansion rate after 2000 cycles = (V2 - V1) / V1 × 100%.

[0133] 2) Capacity retention rate after 2000 cycles

[0134] The secondary batteries in each example and comparative example are subjected to charge and discharge tests at 25 °C in the voltage range of 2.8 - 4.25 V at 1C / 1C. After the SOC is charged from 0% to 100% and then discharged to 0%, it is regarded as one charge and discharge cycle, and this is repeated 2000 times; the capacity retention rate after 2000 cycles (%) = discharge specific capacity of the 2000th cycle / discharge specific capacity of the first cycle × 100%.

[0135] Performance of secondary batteries in each example and comparative example in Table 3

[0136]

[0137]

[0138] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application rather than to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A secondary battery, characterized in that, It includes a positive electrode plate, a composite separator, and a negative electrode plate; The composite separator includes a separator substrate, a first elastic coating provided on one surface of the separator substrate and in contact with the negative electrode plate, and a second elastic coating provided on the other surface of the separator substrate and in contact with the positive electrode plate; The secondary battery satisfies: Ra > Rc; Wherein, Ra represents the elastic recovery rate of the first elastic coating after applying a pressure of 15 MPa; Rc represents the elastic recovery rate of the second elastic coating after applying a pressure of 15 MPa.

2. The secondary battery according to claim 1, wherein The first elastic coating includes a first core-shell structure polymer; the first core-shell structure polymer includes a core layer and a shell layer, the core layer includes at least one of polyurethane and bio-based polycarbonate, and the shell layer includes at least one of polyether and crosslinked polyvinyl alcohol; The second elastic coating includes a second core-shell structure polymer; the second core-shell structure polymer includes an inner core and an outer shell, the inner core includes at least one of polystyrene and bio-based polycarbonate, and the outer shell includes at least one of crosslinked polyvinyl alcohol and methyl methacrylate-methylacrylic acid copolymer.

3. The secondary battery according to claim 2, characterized in that, The particle size D of the first core-shell structure polymer v50 is 1 to 5 μm, and the particle size D of the second core-shell structure polymer v50 is 0.1 to 1 μm.

4. The secondary battery according to claim 2, characterized in that, The mass ratio of the first core-shell structure polymer in the first elastic coating is 90% - 98%; The mass ratio of the second core-shell structure polymer in the second elastic coating is 80% - 90%.

5. The secondary battery according to claim 1, characterized in that, The thickness of the first elastic coating is 0.2 - 5 μm, and the thickness of the second elastic coating is 0.2 - 5 μm.

6. The secondary battery according to claim 1, wherein The porosity of the first elastic coating is 30% - 50%, and the porosity of the second elastic coating is 50% - 80%.

7. The secondary battery according to claim 1, wherein The first elastic coating and / or the second elastic coating further includes a ceramic material, and the ceramic material includes at least one of Al2O3, AlOOH, Mg(OH)2, SiO2, MgO, CaO, and Cr2O3.

8. The secondary battery according to claim 7, wherein The particle size D of the ceramic material v50 is 0.5 to 4 μm.

9. The secondary battery according to claim 8, wherein, The mass ratio of the ceramic material in the first elastic coating or in the second elastic coating is 1% - 10%.

10. The secondary battery according to claim 1, characterized in that, The separator substrate includes a polyolefin and an additive, and the additive includes at least one of ethylene-octene copolymer (POE), ethylene propylene diene monomer rubber, and polyisoprene rubber. The mass ratio of the additive in the separator substrate is 5% - 20%.

11. An electrical device, characterized in that, It includes the secondary battery according to any one of claims 1 to 10, and the secondary battery is used as the power supply of the electrical device.

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