Secondary batteries and methods for preparing them, and electrical equipment.

Abstract

Invention details;

Description

Secondary battery and preparation method thereof, and electrical equipment

[0001] Citation of Related Applications

[0002] This application claims all rights and interests in the invention patent application with application number 202310898227.1 and title “Secondary battery and its preparation method” filed with the State Intellectual Property Office of the People’s Republic of China on July 20, 2023, and incorporates its entire contents into this document by reference.

[0003] field

[0004] The present application relates to the field of new energy, and specifically to secondary batteries and methods for preparing the same.

[0005] background

[0006] In secondary batteries, to improve the heat resistance of the separator, a highly heat-resistant inorganic particle coating can be applied to one or both sides of the base film. However, this coating has a high density, which is not conducive to improving battery performance. Furthermore, the separators currently used in the market suffer from poor adhesion to the positive and negative electrodes. This is especially true in power batteries, where a high degree of adhesion between the separator and the electrode is required to ensure a high degree of battery integrity for easy assembly. However, the relevant coating design requires high temperatures and pressures, and achieving the required adhesion strength is difficult.

[0007] Overview

[0008] The first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator comprises a base film and a coating arranged on at least one side of the base film; the coating is a composite polymer and a binder, and the composite polymer comprises a first polymer in a core layer and a second polymer in a coating layer arranged on the surface of the core layer; the peel strength between the coating and the positive electrode sheet is 1 to 5 N / m; at 130°C for 0.5h, the thermal shrinkage rate of the separator in the MD and TD directions is less than 5%.

[0009] In some embodiments, the peel strength between the separator and the negative electrode sheet is 1 to 5 N / m.

[0010] In certain embodiments, the first polymer comprises at least one of polybenzimidazoleimide, polybenzothiazole, polybenzoxazole, polybenzoxazinone, polyimidazole pyrrolidone, polyethersulfone, polyphenylene sulfide, polyetherketone, polydiphenyl ether, phenyl polyphenylene, polyparaxylene, bisphenol A type polyarylate, polyparahydroxybenzoate, and polyoxalylene.

[0011] In certain embodiments, the second polymer comprises at least one of polyacrylic acid, polyacrylate, nitrile rubber, chloroprene rubber, polyvinyl alcohol, or a copolymer of any two of the foregoing.

[0012] In certain embodiments, the particle size of the composite polymer is 0.1 to 10 μm.

[0013] In certain embodiments, the binder includes at least one of vinylidene fluoride, carboxymethyl cellulose, and styrene-butadiene rubber.

[0014] In certain embodiments, the coating has a thickness of 0.2 to 10 μm.

[0015] The second aspect of the present application provides a method for preparing the secondary battery, comprising adding particles of the first polymer to an emulsion of the second polymer, mixing, stirring, heating, and drying to obtain a composite polymer;

[0016] The composite polymer, binder and water are mixed to form slurry, which is then coated on at least one side of the base film and solidified to form a coating to obtain the separator.

[0017] In certain embodiments, the mass ratio of the particles of the first polymer to the emulsion of the second polymer is (14-20):(1-6).

[0018] In certain embodiments, the mass ratio of the composite polymer to the binder is (90-99.5):(0.5-10).

[0019] A third aspect of the present application provides an electrical device comprising the aforementioned secondary battery.

[0020] In the secondary battery of the present application, in the composite polymer of the coating of the diaphragm, the inner core layer adopts a first polymer with a melting point of 180 to 400°C, and the coating layer adopts a second polymer with a softening temperature of 40 to 70°C. The polymers with high melting point and low softening temperature are combined with each other to play a synergistic role. The constructed composite polymer coating material can achieve high bonding strength and high heat resistance of the composite diaphragm after one coating.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings in the specification, which constitute a part of this application, are used to provide further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute improper limitations on this application.

[0023] FIG1 is a schematic structural diagram of a composite diaphragm according to an embodiment of the present application;

[0024] FIG2 is an electron microscope image of the composite polymer according to one embodiment of the present application.

[0025] Details

[0026] The present application discloses a secondary battery and a method for preparing the same. Those skilled in the art can refer to the contents of this article and appropriately improve the process parameters for implementation. It is particularly important to point out that all similar replacements and modifications are obvious to those skilled in the art, and they are all deemed to be included in this application. The method described in this application has been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods described herein without departing from the content, spirit and scope of this application to implement and apply the technology of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0027] It should be noted that, in this document, if relational terms such as "first" and "second", "step 1" and "step 2", and "(1)" and "(2)" appear, they are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "including a..." do not exclude the presence of other identical elements in the process, method, article or device comprising the elements. At the same time, the embodiments in this application and the features in the embodiments can be combined with each other in the absence of conflict.

[0028] In the first aspect of the present application, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator comprises a base film and a coating disposed on at least one side of the base film; the coating is a composite polymer and a binder, the composite polymer comprising a first polymer of an inner core layer and a second polymer of a coating layer disposed on the surface of the inner core layer; the separator exhibits a peel strength of 1 to 5 N / m from the positive electrode sheet; and the separator exhibits a thermal shrinkage rate of less than 5% in the longitudinal (MD) and transverse (TD) directions at 130°C for 0.5 h. The coating structure comprises an inner core layer and a coating layer, and because the inner core layer is tightly coated by the coating layer, the risk of the polymer of the inner core layer falling off from the separator coating during long-term battery cycling is effectively reduced. In certain embodiments, the peel strength of the separator from the positive electrode sheet can be 1 N / m, 2 N / m, 3 N / m, 4 N / m, 5 N / m, or a range consisting of any two thereof. In some embodiments, at 130°C for 0.5h, the thermal shrinkage rate in the MD and TD directions of the diaphragm can be 0.5%, 1%, 2%, 3%, 4%, 5% or a range consisting of any two of them. The diaphragm of the present application has high heat resistance and adhesion.

[0029] In certain embodiments of the present application, the peel strength between the separator and the negative electrode sheet may be 1 to 5 N / m. In certain examples, the peel strength between the separator and the negative electrode sheet may be 1 N / m, 2 N / m, 3 N / m, 4 N / m, 5 N / m, or a range consisting of any two thereof.

[0030] In certain embodiments of the present application, the first polymer comprises at least one of polybenzimidazoleimide, polybenzothiazole, polybenzoxazole, polybenzoxazinone, polyimidazole pyrrolidone, polyethersulfone, polyphenylene sulfide, polyetherketone, polydiphenyl ether, phenyl polyphenylene, polyparaxylene, bisphenol A polyarylate, polyparahydroxybenzoate, and polyoxalyl urea. The melting point of the above polymer is 180-400°C, which can help the separator have high heat resistance.

[0031] In certain embodiments of the present application, the second polymer comprises at least one of polyacrylic acid, polyacrylate, nitrile rubber, chloroprene rubber, polyvinyl alcohol, or a copolymer of any two of the foregoing. The softening temperature of the polymer is 40-70°C, thereby enabling the separator to have a high bonding strength.

[0032] In certain embodiments of the present application, the polyacrylic acid includes at least one of polyacrylic acid, polymethacrylic acid, poly(2-ethylacrylic acid), poly(2-propylacrylic acid), and polybutylacrylic acid.

[0033] In certain embodiments of the present application, the polyacrylates include at least one of polymethyl methacrylate, polyethyl methacrylate, polyisobutyl methacrylate, polyhydroxypropyl acrylate, polymethyl acrylate, and polybutyl acrylate.

[0034] In certain embodiments of the present application, the polyvinyl alcohols include at least one of polyvinyl alcohol and polyvinyl acetal, wherein the polyvinyl acetal includes at least one of polyvinyl formal, polyvinyl acetal, polyvinyl butyral and polyvinyl furfural.

[0035] In some other embodiments of the present application, the first polymer and the second polymer in the composite polymer include any one of the following combinations:

[0036] Polybenzimidazoleimide and polyacrylic acid, polybenzimidazole and polyacrylate copolymers, polyethersulfone and polyacrylic acid copolymers, polybenzimidazoleimide and polyacrylic acid copolymers.

[0037] In other embodiments of the present application, the mass ratio of the first polymer to the second polymer is (14-20):(1-6). Preferably, it is (15-20):(1-4), and more preferably, it is (16-18):(1-4). The mass ratio of the first polymer to the second polymer within the range of the present application is conducive to coordinating the heat resistance and adhesion of the separator.

[0038] The structural diagram of the composite polymer is shown in Figure 1, and the SEM image is shown in Figure 2. In the composite polymer, the highly heat-resistant first polymer serves as the core, and the highly adhesive second polymer serves as the coating. The highly heat-resistant polymer is tightly coated by the highly adhesive polymer, effectively reducing the risk of the highly heat-resistant polymer falling off from the separator coating during long-term battery cycling. The highly adhesive polymer as the coating effectively bonds to the core polymer and further strengthens the adhesion between the coating and the separator.

[0039] In certain embodiments of the present application, the porosity of the base film is 35% to 60%.

[0040] In certain embodiments of the present application, the composite polymer has a particle size of 0.1 to 10 μm. Preferably, the composite polymer has a particle size of 0.1 to 7 μm, and more preferably, the composite polymer has a particle size of 0.1 to 5 μm. A composite polymer particle size within the range of the present application is beneficial for improving the air permeability of the separator.

[0041] In certain embodiments of the present application, the binder includes at least one of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). The use of a water-based binder in the present application facilitates a tighter bond between the composite polymer and the base film and improves the structural stability of the composite polymer.

[0042] In certain embodiments of the present application, the mass ratio of the composite polymer to the binder in the coating is (90-99.5):(0.5-10). Preferably, it is (93-99):(1-7), and more preferably, it is (95-99):(1-5). The mass ratio of the composite polymer to the binder within the range of the present application is beneficial for improving the overall performance of the separator.

[0043] In certain embodiments of the present application, the coating has a thickness of 0.2 to 10 μm, preferably 0.2 to 7 μm, and more preferably 1 to 5 μm. The thickness of the coating within the range of the present application is conducive to coordinating the high heat resistance, high adhesion and air permeability of the separator.

[0044] In a second aspect of the present application, a method for preparing the secondary battery is provided, comprising adding particles of the first polymer to an emulsion of the second polymer, mixing, stirring, heating, and drying to obtain a composite polymer;

[0045] The composite polymer, binder and water are mixed to form slurry, which is then coated on at least one side of the base film and solidified to form a coating to obtain the separator.

[0046] In certain embodiments of the present application, the first polymer particles can be obtained by in-situ preparation, polymer resin dissolution and re-granulation, etc.; the second polymer is an emulsion polymer.

[0047] In certain embodiments of the present application, the stirring and heating include stirring at 40-100° C. for 0.5-10 h. The heating temperature, in certain embodiments, is 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., 80° C., 85° C., 90° C., 95° C., 100° C., or a range formed by any two values. The stirring time, in certain embodiments, is 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or a range formed by any two values. The stirring and heating conditions within the application range are conducive to promoting uniform mixing of the slurry and will not destroy the structure of the composite polymer.

[0048] In certain embodiments of the present application, the drying temperature is 50° C. to 85° C., and in certain embodiments, 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., 80° C., 85° C., or any two thereof. Stirring, heating, and drying conditions within the applicable range facilitate uniform mixing of the slurry without destroying the structure of the composite polymer.

[0049] In certain embodiments of the present application, the mass ratio of the first polymer particles to the second polymer emulsion in the composite polymer is (14-20):(1-6), preferably (15-20):(1-4), and more preferably (16-18):(1-4). The mass ratio of the first polymer particles to the second polymer emulsion in the composite polymer within the range of the present application is beneficial for coordinating the heat resistance and adhesion of the separator, thereby achieving superior performance of the separator.

[0050] In certain embodiments of the present application, the mass ratio of the composite polymer to the binder is (90-99.5):(0.5-10), preferably (93-99):(1-7), and more preferably (95-99):(1-5).

[0051] In certain embodiments of the present application, the base membrane is a porous base membrane with a porosity of 30% to 80%.

[0052] In certain embodiments of the present application, the base membrane includes any one of a polyolefin porous base membrane, a non-woven porous base membrane, and a polyvinylidene fluoride porous base membrane.

[0053] In certain embodiments of the present application, by testing and comparing the thermal stability, liquid retention rate, ionic conductivity and peel strength of the composite membrane of the present application with other comparative membranes, the results show that the composite membrane of the present application can maintain a relatively good level in all aspects at the same time, especially in thermal stability, liquid retention rate and ionic conductivity, which can be significantly better than the comparative membranes.

[0054] In a third aspect of the present application, an electric device is provided, comprising the above-mentioned secondary battery.

[0055] In certain embodiments of the present application, the coating side of the composite separator is hot-pressed and composited with the positive and negative electrode sheets respectively to perform battery assembly.

[0056] In some other embodiments of the present application, the positive electrode sheet includes a positive electrode active material, which may include at least one of a ternary lithium positive electrode material and a lithium iron phosphate positive electrode material; the negative electrode sheet includes a negative electrode active material, which may include at least one of graphite and a silicon-oxygen composite material; the conductive agent may include carbon black, conductive graphite, VGCF (vapor-grown carbon fiber), carbon nanotubes and graphene, etc.; the binder may include polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA) and its salts, polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA) and at least one of the current collector may be a metal foil with good conductivity, such as at least one of aluminum foil and copper foil; the lithium-ion battery described in the present application may be a full cell, a half cell or a symmetrical cell, or a button cell or a soft-pack cell.

[0057] In certain embodiments of the present application, a 1-1.5M lithium hexafluorophosphate electrolyte may be used as the electrolyte. In certain examples, 1M lithium hexafluorophosphate is used as the lithium salt, and a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1 is used as the solvent to serve as the battery electrolyte.

[0058] In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials, except for the differences noted in each group, were kept consistent to ensure comparability. In addition, all materials used in this application can be purchased from commercial sources.

[0059] The secondary battery and its preparation method provided in this application are further described below.

[0060] Example 1:

[0061] (1) Preparation of diaphragm:

[0062] Providing polybenzimidazole imide (melting point: 270°C) particles with a particle size of 1 μm; providing polyacrylic acid-polymethyl methacrylate copolymer (softening temperature: 50°C) emulsion with a particle size of 0.2 μm;

[0063] Polyacrylic acid-polymethyl methacrylate copolymer was loaded on polybenzimidazole imide particles. Polybenzimidazole imide and polyacrylic acid-polymethyl methacrylate copolymer were mixed in a mass ratio of 17:3, heated to 50°C and stirred for 1 hour, and dried at 60°C to prepare a composite polymer. The SEM electron microscope image of the morphology is shown in Figure 2;

[0064] Adding PVDF aqueous binder to the composite polymer and adding deionized water to prepare a slurry, wherein the amount of the composite polymer added is 98% of the slurry mass, the amount of the aqueous binder added is 2% of the slurry mass, and the amount of deionized water added is 50wt% of the powder mass;

[0065] Providing a porous base film, specifically a polyethylene base film, with a porosity of 40%;

[0066] The slurry was coated on one side of a porous base membrane and dried at 60° C. The thickness of the prepared composite membrane coating was 3 μm.

[0067] (2) Preparation of positive electrode sheet:

[0068] The ternary NCM622 positive electrode active material, polyvinylidene fluoride, and conductive carbon black were added to N-methylpyrrolidone solvent in a mass ratio of 96:2:2, stirred evenly, and coated on aluminum foil. The positive electrode sheet was prepared through drying, rolling, and slitting processes.

[0069] (3) Preparation of negative electrode sheet

[0070] Graphite negative electrode active material, conductive carbon black, and carboxymethyl cellulose (CMC) are added to deionized water in a mass ratio of 96:2:2, stirred evenly, and coated on copper foil. The negative electrode sheet is prepared through drying, rolling, and slitting processes.

[0071] (4) Preparation of electrolyte

[0072] Lithium hexafluorophosphate is dissolved in a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate to prepare an electrolyte, wherein the mass ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 1:1:1; the concentration of lithium hexafluorophosphate in the electrolyte is 1M.

[0073] (5) Battery production

[0074] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator placed between the positive and negative electrode sheets. After winding, hot pressing and shaping, and tab welding, a bare battery cell is obtained. The bare battery cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The prepared electrolyte is injected into the dried battery, allowed to stand, formed, and divided to complete the preparation of the lithium-ion soft-pack battery.

[0075] Other Examples and Comparative Examples:

[0076] The composite membrane was prepared by referring to the preparation method of Example 1, with the differences shown in Table 1 below.

[0077] Table 1

[0078] Adhesion performance between the diaphragm and the electrode: The coated side of the diaphragm was hot-pressed with the positive and negative electrode sheets respectively. The hot-pressing conditions were 60°C and 2 MPa. The peel strength between the diaphragm and the electrode sheet was tested using a universal tensile testing machine and the peel strength was recorded as shown in Table 2.

[0079] Thermal shrinkage performance of the diaphragm: The prepared diaphragm was punched into a fixed size (100 mm × 50 mm) and subjected to thermal shrinkage testing under the test conditions of 100°C / 1 h and 130°C / 0.5 h. The test results are shown in Table 2.

[0080] Ionic conductivity of the diaphragm: A symmetrical battery was prepared using the prepared diaphragm to characterize the ionic conductivity of the diaphragm itself. The test results are shown in Table 2. The specific method for preparing the symmetrical battery is as follows: copper foil is used as an electrode, a conventional lithium-ion battery electrolyte (1M lithium hexafluorophosphate as a lithium salt, ethylene carbonate EC, dimethyl carbonate DMC, and ethyl methyl carbonate EMC mixed in a volume ratio of 1:1:1 as a solvent) is used as the symmetrical battery electrolyte, and then the diaphragm is used to assemble the battery for testing;

[0081] Diaphragm liquid retention: Punch the diaphragm into a certain size and weigh it. After fully soaking it in the above electrolyte, take it out, wipe off the surface electrolyte and weigh it again. Calculate the liquid retention capacity and liquid retention rate, and record the liquid retention rate as shown in Table 2.

[0082] Table 2

[0083] A comparison of Examples 1-5 and Comparative Example 3 shows that when the separator coating comprises a core comprising a polymer with a melting point of 180°C to 400°C and a coating comprising a polymer with a softening temperature of 40°C to 70°C, it significantly impacts the separator's peel strength, thermal shrinkage, ionic conductivity, and liquid retention. The highly heat-resistant polymer and the polymer with an appropriate softening temperature act synergistically in the separator coating, significantly improving both the separator's bonding strength and heat resistance.

[0084] A comparison of Example 1 and Comparative Examples 1 and 2 shows that when the separator coating lacks a high-heat-resistant polymer, its heat resistance is poor, and when the separator coating lacks a high-adhesion polymer, its adhesion strength is poor. Furthermore, Examples 1 and 7-9 show that the mass ratio of the high-heat-resistant polymer to the high-adhesion polymer has a certain impact on the performance of the separator. When the mass ratio of the high-heat-resistant polymer to the high-adhesion polymer is controlled within the range of this application, it is beneficial to balance the heat resistance and adhesion strength of the separator.

[0085] In summary, the diaphragm coating used in this application has a good effect of improving the performance of the diaphragm.

[0086] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

DEPCT691. A secondary battery comprising a positive electrode plate, a negative electrode plate, and a separator, in which the separator consists of a base membrane and a coating layer laid on at least one surface of the base membrane; the coating layer consists of a polymer composite and a polymer binder consisting of a primary polymer for the core layer and a secondary polymer for the cladding layer laid on the surface of the core layer; the peel tensile strength between the separator and the positive electrode plate is 1-5 N / m, and the thermal shrinkage of the separator in the MD and TD directions is less than 5% at 130°C for 0.5 hours.

2. A secondary battery according to claim 1 in which the peel tensile strength between the separator and the negative electrode plate is 1-5 N / m. 3.Secondary battery under claim 1 or 2 in which the primary polymer is composed of at least one of the following: polybenzimidazoleimide, polybenzothiazole, polybenzazole, polybenzoxazinone, polyimidazopirolone, polyether sulfone, polyphenylene sulfide, polyether ketone, polydiphenyl ether phenyl, polyphenylene, polyparaxylene, bisphenol A poly(para-hydroxybenzoate) polyarylate, and polyparabanic acid.

4. Secondary battery under claim 1 or 2 in which the melting point of the primary polymer is: 180-400 degrees Celsius.

5. A secondary battery under claim 1 or 2 in which the second polymer is composed of at least one type of polyacrylate, polyacrylate, nitrile rubber, chloroprene rubber, polyvinyl alcohol, and a copolymer formed from any two of them.

6. A secondary battery under claim 1 or 2 in which the softening temperature of the second polymer is 40-70 degrees Celsius.

7. A secondary battery under claim 1 or 2 in which the particle size of the composite polymer is 0.1-10 micrometers. 8.Secondary batteries under claim 1 or 2 in which the binder consists of at least one type of vinylidine fluoride, carboxymethyl cellulose, and styrene-butadiene rubber.

9. Secondary batteries under claim 1 or 2 in which the thickness of the coating layer is 0.2-10 micrometers.

10. Method of preparation for the separator of the secondary battery under claim 1 or 2 consisting of: adding particles of the first polymer to an emulsion of the second polymer, then mixing, heating, and drying to obtain a composite polymer.

10. Preparation method for secondary battery separators according to claim 10 in which stirring and heating are carried out at 40-100°C and stirring for 0.5-10 hours.

11. Preparation method for secondary battery separators according to claim 10 in which drying is carried out at 50-85°C. 13.Methods of preparation for the separator of a secondary battery according to claim 10 where the mass ratio of the particles of the first polymer to the emulsion of the second polymer is (14-20):(1-6).

14. Methods of preparation for the separator of a secondary battery according to claim 10 where the mass ratio of the polymer composite to the binder is (90-99.5):(0.5-10).

15. Electrical devices incorporating a secondary battery according to claim 1 or 2;

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