Diaphragm and preparation method thereof, battery and electric device

Abstract

The invention discloses a diaphragm and a preparation method thereof, a battery and a power utilization device, the diaphragm comprises a porous base membrane and a coating, and the coating is arranged on at least one surface of the porous base membrane; the coating comprises graphene oxide and a perovskite type solid electrolyte. Therefore, the diaphragm disclosed by the invention has relatively good heat resistance and mechanical strength, and the safety performance of the battery can be improved; besides, the diaphragm has good electrolyte wettability, and can effectively reduce obstruction in the ion transmission process, promote uniform and efficient transmission of ions and reduce the generation phenomenon of lithium dendrites, thereby effectively prolonging the service life of the battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a diaphragm and a preparation method thereof, a battery and an electrical device. Background Art

[0002] At present, battery separators on the market are mainly made of organic materials such as polyethylene (PE) or polypropylene (PP). These polyolefin materials have high crystallinity and lack polar groups in the molecular chain. This makes it less compatible with polar electrolytes, resulting in weaker wetting ability of the electrolyte on the separator, thereby limiting the transmission of lithium ions in the internal pores and increasing the polarization of the battery. Uneven lithium ion transmission may further lead to lithium dendrite growth or local lithium precipitation. Summary of the invention

[0003] The present application aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one purpose of the present application is to propose a diaphragm and a preparation method thereof and an electrochemical device. The diaphragm of the present application shows excellent performance in terms of compatibility with the electrolyte and can effectively improve the wettability of the electrolyte. This characteristic effectively reduces the interfacial impedance and reduces the concentration polarization phenomenon inside the battery, thereby improving the overall battery performance.

[0004] Therefore, in the first aspect of the present application, the present application proposes a diaphragm. According to an embodiment of the present application, the diaphragm includes: a porous base film and a coating, the coating is arranged on at least one surface of the porous base film; the coating contains graphene oxide and a perovskite-type solid electrolyte. As a result, the diaphragm of the present application has good heat resistance and mechanical strength, and can improve the safety performance of the battery; in addition, the diaphragm has good electrolyte wettability, can effectively reduce obstacles in the ion transmission process, promote uniform and efficient ion transmission, and reduce the generation of lithium dendrites, thereby effectively extending the service life of the battery.

[0005] According to an embodiment of the present application, the diaphragm may further include at least one of the following additional technical features:

[0006] According to an embodiment of the present application, the mass ratio of the graphene oxide to the perovskite-type solid electrolyte is 1:(1-3).

[0007] According to an embodiment of the present application, the thickness of the coating is 0.01 μm-5 μm.

[0008] According to an embodiment of the present application, the molecular formula of the perovskite solid electrolyte is Li 2x-y Sr 1-x Ta y Zr 1-y O3, where 0.60≤y≤0.75, x=0.75y.

[0009] According to an embodiment of the present application, the particle size of the perovskite solid electrolyte is 0.02 μm-10 μm.

[0010] According to an embodiment of the present application, the thickness of the porous base membrane is 5 μm-20 μm.

[0011] According to an embodiment of the present application, the porosity of the porous base membrane is 30% to 50%.

[0012] According to an embodiment of the present application, the pore size of the porous base membrane is 0.01 μm-0.3 μm.

[0013] According to an embodiment of the present application, the porous base membrane includes at least one of a polyethylene film, a polypropylene film, a polyimide film, a polyethylene terephthalate film, a polyvinylidene fluoride film, a polyvinylidene fluoride-hexafluoropropylene copolymer film, a polyetheretherketone film, a polymethyl methacrylate film, a polyetherimide film, a polyaramid film and a cellulose film.

[0014] In the second aspect of the present application, the present application proposes a method for preparing the diaphragm described in the first aspect. According to an embodiment of the present application, the method comprises: loading a slurry containing graphene oxide and a perovskite solid electrolyte on at least one surface of the porous base film to form a coating; drying the porous base film with the coating to obtain the diaphragm. Therefore, the method of the present application has a simple preparation process, simple operation, can be applied to industrial production, and is easy to quickly achieve mass production. In addition, the diaphragm prepared by this method has excellent heat resistance, mechanical strength and electrolyte wettability, which not only improves the safety performance of the battery, but also can effectively reduce the obstacles in the ion transmission process, promote uniform and efficient ion transmission, and extend the service life of the battery.

[0015] According to an embodiment of the present application, the method may further include at least one of the following additional technical features:

[0016] According to an embodiment of the present application, the slurry further includes a solvent and a binder.

[0017] According to an embodiment of the present application, the mass ratio of the solvent, the binder, the graphene oxide and the perovskite-type solid electrolyte is 100:(0.05-0.1):(0.05-0.5):(0.05-1.5).

[0018] According to an embodiment of the present application, the drying process is performed at 35° C.-45° C. for 10 h-15 h.

[0019] In the third aspect of the present application, the present application proposes a battery. According to an embodiment of the present application, the battery includes the diaphragm described in the first aspect and the diaphragm prepared by the method described in the second aspect. As mentioned above, the diaphragm of the present application not only has excellent heat resistance, mechanical strength and electrolyte wettability, but also can effectively reduce the obstacles in the ion transmission process, promote uniform and efficient transmission of ions, and reduce the formation of lithium dendrites. As a result, the battery of the present application has good safety performance, high temperature resistance and long cycle performance. Those skilled in the art can understand that the battery has all the characteristics and advantages of the diaphragm described above, and will not be repeated here.

[0020] In the fourth aspect of the present application, the present application proposes an electrical device. According to an embodiment of the present application, the electrical device includes the battery described in the third aspect. As mentioned above, the battery of the present application has good safety performance, high temperature resistance and long cycle performance. Therefore, the electrical device of the present application has good high temperature resistance and excellent service life and safety performance. Those skilled in the art can understand that the electrical device has all the features and advantages of the battery described above, and will not be described in detail here.

[0021] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0023] Figure 1 A schematic diagram of the diaphragm structure of the present application is shown;

[0024] Figure 2 An optical comparison diagram of the diaphragms prepared in Example 1 of the present application and Comparative Example 1 is shown;

[0025] Figure 3 The SEM image corresponding to the surface coating of the diaphragm prepared in Example 1 of the present application is shown;

[0026] Figure 4 The Li / Li symmetric battery charge and discharge time-voltage curve corresponding to the diaphragm prepared in Example 1 and Comparative Example 1 of the present application is shown;

[0027] Reference numerals: 01 is a porous base film, and 02 is a coating layer. DETAILED DESCRIPTION

[0028] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0029] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0031] In this document, the terms "include" or "comprising" are open expressions, that is, including the contents specified in the present application but not excluding other contents.

[0032] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Further, in the description of this application, unless otherwise specified, the meaning of "plurality" is two or more.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0034] Modifying polyolefin separators by coating functional materials is the main way to improve the performance of battery separators. Commercial lithium-ion power batteries mainly achieve the purpose of increasing the hardness of the separator, reducing high-temperature thermal shrinkage, increasing tortuosity, and slowing down self-discharge by coating inorganic ceramic materials (alumina, boehmite, etc.) on the separator. However, the existing ceramic composite separators have no significant improvement in the affinity of the electrolyte. The intrinsic ionic conductivity of ceramics is low, and the nano-ceramic particles densely coated on the surface of the porous polyolefin separator will block the ion transmission path and increase the internal resistance. In addition, the thermal performance of ceramic-coated separators has been limited, and it is difficult to meet the growing energy density and safety requirements of lithium-ion power batteries.

[0035] In view of this, the present application proposes a new type of diaphragm to address the deficiencies of existing commercial polyolefin-based diaphragms for lithium-ion batteries in terms of electrolyte wettability, ion conductivity, and high-temperature performance and other safety aspects. The diaphragm is loaded with a coating containing graphene oxide and perovskite-type solid electrolytes, which can effectively enhance the heat resistance and mechanical strength of the diaphragm and improve its safety performance; at the same time, it improves the wettability of the diaphragm to the electrolyte, reduces obstacles in the ion transmission process, promotes uniform and efficient ion transmission, reduces the formation of lithium dendrites, and thus extends the service life of the battery. The diaphragm of the present application, its preparation method, and electrochemical device will be introduced in detail below.

[0036] Diaphragm

[0037] The present application proposes a diaphragm. According to the embodiments of the present application, reference Figure 1 The separator comprises: a porous base membrane 01 and a coating 02, wherein the coating 02 is arranged on at least one surface of the porous base membrane 01; the coating comprises graphene oxide and a perovskite-type solid electrolyte.

[0038] The diaphragm of the present application has achieved the optimization of multiple performances by introducing graphene oxide and perovskite solid electrolyte. Among them, graphene oxide rich in oxygen-containing groups improves the wettability of the diaphragm to the electrolyte, reduces the interfacial impedance, and reduces the concentration polarization in the battery. The hydrophilic nature of these oxygen-containing groups and the stacked porous structure of graphene oxide work together to promote ion exchange. At the same time, the high thermal conductivity of graphene oxide can quickly conduct heat, avoid the generation of local hot spots, and thus inhibit the growth of lithium dendrites. In addition, the high temperature resistance and insulation performance of graphene oxide, as well as its excellent mechanical properties, effectively prevent the short circuit and micro-short circuit caused by the contact of positive and negative electrodes at high temperatures, delay thermal runaway, and enhance the safety of the battery. Perovskite solid electrolyte has high ionic conductivity, can construct additional ion transmission channels, improve the kinetic performance of the battery, and reduce the reaction barrier. In addition, the perovskite solid electrolyte can also adsorb transition metal ions dissolved from the positive electrode, protect the negative electrode from corrosion, and further improve the service life of the battery. In addition, the synergistic effect of the perovskite solid electrolyte and graphene oxide regulates the ion flux distribution, induces uniform lithium removal / intercalation behavior, prevents the growth of lithium dendrites, improves the long cycle performance of the battery, and slows down self-discharge. Therefore, the separator of the present application not only improves the safety performance of the battery, but also effectively extends the service life of the battery through multiple mechanisms.

[0039] In some embodiments of the present application, the mass ratio of the graphene oxide to the perovskite solid electrolyte is 1:(1-3). For example, it can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, etc., or it can be a range composed of any of the above numerical values. Therefore, by making the mass ratio of graphene oxide and perovskite solid electrolyte within the above range, on the one hand, it is possible to optimize the structure and number of ion transmission channels, so that the diaphragm has good electrical conductivity while ensuring its mechanical strength to avoid rupture or deformation during battery use. On the other hand, it can enable the diaphragm to have good thermal management capabilities to avoid battery performance degradation or safety problems caused by excessive temperature.

[0040] In some embodiments of the present application, the thickness of the coating is 0.01 μm-5 μm. For example, it can be 0.01 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc., or it can be a range composed of any of the above values. Thus, by making the thickness of the coating within the above range, it is possible to ensure that the coating is evenly distributed on the diaphragm, while enabling graphene oxide and perovskite-type solid electrolytes to function better. A coating that is too thick may increase the internal resistance of the battery and reduce the migration speed of ions; while a coating that is too thin may not be able to perform the functions of graphene oxide and perovskite-type solid electrolytes well.

[0041] In some embodiments of the present application, the molecular formula of the perovskite solid electrolyte is Li 2x-y Sr 1-x Ta y Zr 1- y O3, where 0.60≤y≤0.75, x=0.75y. For example, it can be Li 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3、Li 0.3 Sr 0.55 Ta 0.6 Zr 0.4 O3、Li 0.325 Sr 0.5125 Ta 0.65 Zr 0.35 O3、Li 0.35 Sr 0.475 Ta 0.7 Zr 0.3 O3, etc., or can be a range of any of the above values. Therefore, the above-mentioned perovskite-type solid electrolytes all have high ionic conductivity, which can increase the ion migration speed inside the battery, thereby improving the charge and discharge efficiency of the battery. In addition, the above-mentioned perovskite-type solid electrolytes can construct additional ion transmission channels, which help to transmit lithium ions faster during the battery charge and discharge process and improve the battery's kinetic performance.

[0042] In some embodiments of the present application, the particle size of the perovskite solid electrolyte is 0.02 μm-10 μm. For example, it can be 0.02 μm, 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, etc., or it can be a range composed of any of the above values. According to an embodiment of the present application, the particle size of the perovskite solid electrolyte is 0.1 μm-1 μm.

[0043] It should be noted that the perovskite solid electrolyte of the present application can be prepared by conventional methods in the art. 2x-y Sr 1-x Ta y Zr 1-yO3, weigh Li2CO3, SrCO3, ZrO2 and Ta2O5 precursor powders according to a certain stoichiometric ratio. After preliminary mixing, add ethanol and grind using a ball mill. The ground powder is dried and pre-calcined. After the pre-calcined powder is cooled to room temperature, a polyvinyl alcohol aqueous solution is added, ground and granulated, and tablets are formed by cold isostatic pressing. The tablets are debinded at high temperature, cooled to room temperature, and covered with the same mother powder for further calcination. After the calcined tablets are cooled to room temperature, they are ground to obtain perovskite solid electrolyte powders, and perovskite solid electrolyte nanoparticles are obtained by sieving and flotation. Among them, in order to improve the quality of the product, additional Li2CO3 can be appropriately introduced as a supplement on the basis of the corresponding stoichiometric ratio, in order to make up for the loss of key substances that may occur during the preparation process due to process losses or incomplete reactions. Further preferably, the mass of the additional Li2CO3 is 1%-5% of the original stoichiometric ratio.

[0044] In some embodiments of the present application, the thickness of the porous base film is 5 μm-20 μm, for example, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc., or a range of any of the above values.

[0045] In some embodiments of the present application, the porosity of the porous base film is 30% to 50%, for example, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, etc., or a range of any of the above values.

[0046] In some embodiments of the present application, the pore size of the porous base membrane is 0.01 μm-0.3 μm, for example, 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, etc., or a range of any of the above values.

[0047] It should be noted that the particle size of the perovskite solid electrolyte of the present application is larger than the pore size of the porous base membrane, thereby effectively reducing the risk of perovskite solid electrolyte particles blocking the pores of the porous base membrane, ensuring the smooth transmission of lithium ions inside the battery, thereby maintaining the high ionic conductivity and good charge and discharge performance of the battery. According to an embodiment of the present application, the pore size of the porous base membrane is 0.01μm, and the particle size of the perovskite solid electrolyte is 0.02μm-10μm. According to an embodiment of the present application, the pore size of the porous base membrane is 0.3μm, and the particle size of the perovskite solid electrolyte is 0.31μm-10μm.

[0048] In some embodiments of the present application, the porous base film includes but is not limited to at least one of polyethylene film, polypropylene film, polyimide film, polyethylene terephthalate film, polyvinylidene fluoride film, polyvinylidene fluoride-hexafluoropropylene copolymer film, polyetheretherketone film, polymethyl methacrylate film, polyetherimide film, polyaramid film and cellulose film. Thus, the porous base film of the above type is a porous structure, which is conducive to the transmission of lithium ions.

[0049] In some embodiments of the present application, the graphene oxide is lamellar. It should be noted that the present application does not specifically limit the specific sheet diameter, thickness and number of monolayers of graphene oxide. As long as its structure is lamellar. Exemplarily, the sheet diameter of the graphene oxide can be 0.5μm-5μm, for example, it can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, etc., or it can be a range composed of any of the above numerical values. Exemplarily, the thickness of the graphene oxide can be 0.5nm-1.5nm, for example, it can be 0.5nm, 0.8nm, 1nm, 1.2nm, 1.5nm, etc., or it can be a range composed of any of the above numerical values. Exemplarily, the number of monolayers of the graphene oxide can be 1-3 layers, for example, it can be 1 layer, 2 layers, 3 layers, etc., or it can be a range composed of any of the above numerical values.

[0050] In some embodiments of the present application, the coating can be disposed on one side of the porous base membrane or on both sides of the porous base membrane. When the coating is disposed on both sides of the porous base membrane, the coating thickness on both sides can be the same or different.

[0051] Method for preparing diaphragm

[0052] The present application proposes a method for preparing the aforementioned diaphragm. According to an embodiment of the present application, the method comprises: loading a mixed solution containing graphene oxide and a perovskite-type solid electrolyte on at least one surface of a porous base film to form a coating; drying the porous base film with the coating to obtain the diaphragm. As a result, the preparation process of the present application is simple and efficient, and has high compatibility with existing production processes. It can be adjusted and optimized slightly on the existing production line, so that the product can be rapidly industrialized and easily mass-produced. In addition, the diaphragm prepared by this method has excellent heat resistance, mechanical strength and electrolyte wettability, which not only improves the safety performance of the battery, but also can effectively reduce the obstacles in the ion transmission process, promote uniform and efficient ion transmission, and extend the service life of the battery.

[0053] In some embodiments of the present application, the mixed solution further includes a solvent and a binder, wherein the graphene oxide, the perovskite-type solid electrolyte and the binder are all soluble in the solvent.

[0054] In some embodiments of the present application, the mass ratio of the solvent, the binder, the graphene oxide and the perovskite solid electrolyte is 100:(0.05-0.1):(0.05-0.5):(0.05-1.5). For example, it can be 100:0.05:0.05:0.05, 100:0.05:0.1:0.1, 100:0.05:0.3:1, 100:0.07:0.3:1, 100:0.1:0.5:1.5, etc., or can be a range composed of any of the above numerical values.

[0055] In some embodiments of the present application, the solvent includes but is not limited to at least one of deionized water, N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,2-dimethoxyethane, dimethyl sulfoxide, diethyl carbonate, ethyl methyl carbonate, tetrahydrofuran, ethanol, ethylene glycol, ethylene glycol dimethyl ether and isopropanol.

[0056] In some embodiments of the present application, the binder includes but is not limited to at least one of polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose-sodium (CMC-Na) and styrene-butadiene rubber (SBR).

[0057] In some embodiments of the present application, the drying process is carried out at 35°C-45°C for 10h-15h. According to an embodiment of the present application, the temperature of the drying process may be 35°C, 37°C, 40°C, 42°C, 45°C, etc., or may be a range consisting of any of the above numerical values. According to an embodiment of the present application, the drying time may be 10h, 11h, 12h, 13h, 14h, 15h, etc., or may be a range consisting of any of the above numerical values. Thus, it helps to fix the coating on the base film, ensuring that the coating is evenly distributed and not easy to fall off.

[0058] In some embodiments of the present application, the loading method can be conventional means, as long as the coating can be fixed on the surface of the porous base film. Exemplarily, the loading method can include but is not limited to at least one of spin spraying, dip coating, blade transfer coating, micro-concave roller coating, printing coating, extrusion coating, wire rod coating and vacuum filtration.

[0059] Batteries and electrical devices

[0060] The present application proposes a battery. According to an embodiment of the present application, the battery includes the aforementioned diaphragm or a diaphragm prepared by the aforementioned method. In general, the battery includes an electrolyte, a battery cell, and a packaging material for encapsulating the battery cell. The battery cell includes a positive electrode sheet, a negative electrode sheet, and a composite diaphragm located between the positive electrode sheet and the negative electrode sheet. The battery can be prepared according to conventional methods in the art, for example, the above-mentioned positive electrode sheet, composite diaphragm, and negative electrode sheet are stacked in sequence and then wound or stacked into a battery cell, and then the battery cell is encapsulated with a packaging material (such as an aluminum-plastic film, etc.) and injected with an electrolyte, and then vacuum encapsulated, left to stand, formed, shaped, sorted, and other processes to form an electrochemical device.

[0061] Furthermore, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on the surface of the current collector, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent, wherein the mass percentage of the positive electrode active material is 60%-96%, for example, 60%, 70%, 80%, 90%, 96% or a range consisting of any two thereof; the mass percentage of the conductive agent is 1%-10%, for example, 1%, 2%, 5%, 10% or a range consisting of any two thereof; the mass percentage of the binder is 1%-10%, for example, 1%, 2% , 5%, 10% or any two thereof; wherein the positive electrode active material is selected from one or more of lithium cobalt oxide (LCO), lithium manganese oxide, lithium iron phosphate (LFP), nickel cobalt manganese (NCM) ternary materials, and nickel cobalt aluminum (NCA) layered materials; the positive electrode current collector can be an aluminum foil composed mainly of aluminum, or a composite current collector formed by pressing aluminum foil with other materials (such as polymer materials, etc.), or a composite current collector including aluminum foil and a conductive carbon layer coated on the surface of the aluminum foil, etc., wherein the mass content of aluminum in the aluminum foil is generally not less than 95%.

[0062] For example, in the preparation process of the positive electrode sheet, the positive electrode active material, the binder, and the conductive agent are mixed in a certain weight ratio, and a solvent such as N-methylpyrrolidone (NMP) or water is added, and stirred under the action of a vacuum mixer until the mixed system forms a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated on an aluminum foil with a thickness of 8-15 μm; the aluminum foil coated with the positive electrode slurry is baked and dried in an oven, and then rolled and cut to obtain a positive electrode sheet.

[0063] Further, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the current collector, wherein the negative electrode active material layer includes a negative electrode active material, a binder, and a conductive agent, wherein the mass percentage of the negative electrode active material is 60%-96%, such as 60%, 70%, 80%, 90%, 96% or a range consisting of any two thereof; the mass percentage of the conductive agent is 1%-10%, such as 1%, 2%, 5%, 10% or a range consisting of any two thereof; the mass percentage of the binder is 1%-10%, such as 1%, 2%, 5%, 10% or a range consisting of any two thereof; wherein the negative electrode active material is selected from one or more of artificial graphite, natural graphite, silicon, and silicon dioxide. The negative electrode current collector includes, for example, copper foil, etc.

[0064] For example, in the preparation process of the negative electrode sheet, the negative electrode active material, the conductive agent, and the binder are added to the dispersant to form the negative electrode slurry by a wet process; the negative electrode slurry is evenly coated on a copper foil with a thickness of 4-10 μm; the copper foil coated with the negative electrode slurry is baked and dried in an oven, and then rolled and cut to obtain the negative electrode sheet, wherein the dispersant can be, for example, sodium carboxymethyl cellulose (CMC).

[0065] In the present invention, the conductive agent may include at least one of conductive carbon black (SP), acetylene black, Ketjen black, carbon fiber, etc., and the binder may be at least one of polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, carboxymethyl cellulose sodium (CMC), polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber (SBR).

[0066] Optionally, the above-mentioned electrolyte may include a non-aqueous electrolyte, whose components may include a non-aqueous solvent and a lithium salt, the non-aqueous solvent includes carbonates and / or carboxylates, such as ethylene carbonate, propylene carbonate, propyl propionate, ethyl propionate; the lithium salt includes lithium hexafluorophosphate (LiPF6) and / or lithium tetrafluoroborate (LiBF4). In addition, the electrolyte may also contain additives, which may be conventional electrolyte additives in the art, such as at least one of lithium trifluoromethyl triethylborate, propenyl-1,3-sultone, and fluoroethylene carbonate.

[0067] The battery of the present application may include a battery cell form, a battery module form and a battery pack form. In some embodiments, the battery cells can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module. In some embodiments, the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0068] The present application proposes an electrical device. According to an embodiment of the present application, the electrical device includes the aforementioned battery. As mentioned above, the battery has good safety performance, high temperature resistance and long cycle performance. Therefore, the electrical device of the present application has good high temperature resistance and excellent service life and safety performance. Those skilled in the art can understand that the electrical device has all the features and advantages of the aforementioned battery, which will not be described in detail here.

[0069] Battery cells, battery modules, and battery packs can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0070] As an electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0071] As an embodiment, the electric device may be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electric device for high power and high energy density of the battery, a battery pack or a battery module may be used.

[0072] As another embodiment, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery cell may be used as a power source.

[0073] The scheme of the present application will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are indicated in the embodiments, the technology or conditions described in the literature in this area or the product specification are carried out. The reagents used or the instruments that do not indicate the manufacturer are all conventional products that can be obtained commercially.

[0074] Example 1

[0075] 1. Preparation of perovskite solid electrolyte

[0076] According to the molecular formula Li 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 stoichiometric ratio, weigh 0.4362g Li2CO3, 1.9377g SrCO3, 0.9243g ZrO2 and 4.9743g Ta2O5 precursor powder (5% excess Li2CO3). After preliminary mixing, place in a 50ml ball mill, add 40ml ethanol, and ball mill at 800 rpm for 15 hours. Place the ground slurry in a vacuum drying oven and dry at 120℃ for 8 hours. Pre-calcine the dried product powder in a muffle furnace. Heat to 1100℃ with a heating rate of 5℃ / min, and keep warm for 12 hours after reaching the target temperature. After the pre-calcined powder is cooled to room temperature, take 1.2g, gradually add 0.7ml 5% polyvinyl alcohol aqueous solution, grind and granulate in a mortar, and make 12mm tablets at 200MPa by cold isostatic pressing. The tablets were heated to 650°C in a muffle furnace at 1°C / min and kept warm for 2 hours to remove polyvinyl alcohol. After cooling to room temperature, the tablets were covered with the same mother powder of about 2 times the mass of the tablets and placed in a muffle furnace for calcination. Heated to 1300°C at a heating rate of 5°C / min, and kept warm for 15 hours after reaching the target temperature. After cooling to room temperature, the Li 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 perovskite solid electrolyte powder. The powder was sieved and dispersed in deionized water, and ultrasonically treated to obtain a suspension. After standing for 2 hours, the upper part of the suspension was collected to obtain Li 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 perovskite solid electrolyte nanoparticles with a particle size of 0.1μm.

[0077] 2. Preparation of coating slurry

[0078] Take 50 mg of CMC-Na, add it into 100 ml of deionized water, and obtain dispersion 1 after ultrasonic dispersion;

[0079] 100 mg of graphene oxide powder was added to dispersion 1, and then ultrasonically dispersed after stirring to obtain dispersion 2;

[0080] Take 100 mg of Li obtained in step 1 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 perovskite solid electrolyte nanoparticles are added to dispersion 2, stirred and ultrasonically dispersed to obtain dispersion 3, thereby obtaining a coating slurry.

[0081] 3. Preparation of Diaphragm

[0082] The porous base membrane is selected from a circular commercial wet-process double-drawn polyethylene membrane with a diameter of 4 cm, the thickness of the porous base membrane is 7 μm, the porosity is 42%, the pore size is 0.05 μm, and 2 mg of the dispersion 3 obtained in step 2. The coating slurry is tightly loaded on the membrane using a vacuum filtration method to form a coating with a thickness of 2 μm. After the membrane is dried in a vacuum oven at 40°C for 12 hours, it is cut into discs with a diameter of 19 mm using a sheet puncher.

[0083] Example 2

[0084] The separator was prepared according to the method described in Example 1, except that in step 2, 200 mg of Li obtained in step 1 was added to the dispersion 2. 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 perovskite solid electrolyte nanoparticles.

[0085] Example 3

[0086] The separator was prepared according to the method described in Example 1, except that in step 2, 300 mg of Li obtained in step 1 was added to the dispersion 2. 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 perovskite solid electrolyte nanoparticles.

[0087] Example 4

[0088] The separator was prepared according to the method described in Example 1, except that in step 2, 50 mg of Li obtained in step 1 was added to the dispersion 2. 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 perovskite solid electrolyte nanoparticles.

[0089] Example 5

[0090] The separator was prepared according to the method described in Example 1, except that in step 2, 500 mg of Li obtained in step 1 was added to the dispersion 2. 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 perovskite solid electrolyte nanoparticles.

[0091] Example 6

[0092] A diaphragm was prepared according to the method described in Example 1, except that the thickness of the coating in step 3 was 1 μm.

[0093] Example 7

[0094] A diaphragm was prepared according to the method described in Example 1, except that the thickness of the coating in step 3 was 3 μm.

[0095] Example 8

[0096] A diaphragm was prepared according to the method described in Example 1, except that the thickness of the coating in step 3 was 5 μm.

[0097] Example 9

[0098] A diaphragm was prepared according to the method described in Example 1, except that the thickness of the coating in step 3 was 8 μm.

[0099] Example 10

[0100] The diaphragm was prepared according to the method described in Example 1, except that in step 3, the porous base membrane was selected from a circular commercial polyethylene membrane with a diameter of 4 cm, the porous base membrane had a thickness of 7 μm, a porosity of 37%, and a pore size of 0.05 μm.

[0101] Embodiment 11

[0102] The diaphragm was prepared according to the method described in Example 1, except that in step 3, the porous base membrane was selected from a circular commercial polypropylene membrane with a diameter of 4 cm, the porous base membrane had a thickness of 12 μm, a porosity of 50%, and a pore size of 0.05 μm.

[0103] Example 12

[0104] The diaphragm was prepared according to the method described in Example 1, except that the molecular formula of the perovskite solid electrolyte in step 1 is Li 0.3 Sr 0.55 Ta 0.6 Zr 0.4 O3, particle size is 0.1μm.

[0105] Example 13

[0106] The diaphragm was prepared according to the method described in Example 1, except that the molecular formula of the perovskite solid electrolyte in step 1 is Li 0.35 Sr 0.475 Ta 0.7 Zr 0.3 O3, particle size is 0.1μm.

[0107] Comparative Example 1

[0108] The comparative example diaphragm adopts the commercial wet-process biaxially stretched polyethylene diaphragm substrate described in Example 1 without any modification, and is cut into discs with a diameter of 19 mm by a punching machine.

[0109] Comparative Example 2

[0110] In this comparative example, the coating slurry contains only graphene oxide, solvent and binder, and the specific process of preparing the diaphragm is as follows:

[0111] Take 50 mg of CMC-Na, add it into 100 ml of deionized water, and obtain dispersion 1 after ultrasonic dispersion.

[0112] 200 mg of graphene oxide powder was added to dispersion 1, and then ultrasonically dispersed after stirring to obtain dispersion 2, i.e., coating slurry.

[0113] Take a circular commercial wet-process double-stretched polyethylene separator with a diameter of 4 cm and 2 mg of dispersion 2. Use vacuum filtration to load the coating slurry tightly on the separator to form a coating. After drying the separator in a vacuum oven at 40°C for 12 hours, use a sheet puncher to cut it into a disc with a diameter of 19 mm.

[0114] Comparative Example 3

[0115] In this comparative example, the coating slurry contains only a perovskite-type solid electrolyte, a solvent and a binder. The perovskite-type solid electrolyte is prepared according to the method described in Example 1. The specific process of preparing the diaphragm is as follows:

[0116] Take 50 mg of CMC-Na, add it into 100 ml of deionized water, and obtain dispersion 1 after ultrasonic dispersion.

[0117] 200 mg of the perovskite solid electrolyte prepared in Example 1 was added to the dispersion 1, and then stirred and ultrasonically dispersed to obtain the dispersion 2, i.e., the coating slurry.

[0118] Take a circular commercial wet-process double-stretched polyethylene separator with a diameter of 4 cm and 2 mg of dispersion 2. Use vacuum filtration to load the coating slurry tightly on the separator to form a coating. After drying the separator in a vacuum oven at 40°C for 12 hours, use a sheet puncher to cut it into a disc with a diameter of 19 mm.

[0119] The differences between the diaphragms prepared in Examples 1-13 and Comparative Examples 1-3 are shown in Table 1.

[0120] Table 1

[0121]

[0122]

[0123] Detection and analysis

[0124] 1. The membranes prepared in Example 1 and Comparative Example 1 were subjected to optical analysis. Figure 2As shown, compared with the diaphragm of Comparative Example 1 which is not loaded with a coating, the diaphragm loaded with a coating in Example 1 appears black, indicating that the surface of the diaphragm prepared by the method of the present application is successfully loaded with a coating.

[0125] The separators prepared in Examples 2-13 also appear black, indicating that they are also successfully loaded with the coating.

[0126] 2. SEM morphology analysis

[0127] The surface microstructure of the diaphragm prepared in Example 1 was analyzed using a scanning electron microscope (SEM). Figure 3 As shown, it can be observed that the polyethylene separator matrix contains graphene oxide and Li 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 perovskite solid electrolyte nanoparticles, in which Li 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 perovskite solid electrolyte nanoparticles are loaded on graphene oxide. The two form a dense and uniform coating on the polyethylene diaphragm substrate, covering most of the holes on the diaphragm substrate. The lamellar graphene oxide nanoparticles are staggered and stacked on the polyethylene substrate to form a two-dimensional porous grid structure. Some solid electrolyte nanoparticles are anchored at multiple connection sites of the interlayer grid structure, and the rest are distributed on the surface of the graphene oxide nanosheets.

[0128] The surface microstructure of the membrane prepared in Example 2-13 was analyzed by scanning electron microscopy. As shown in the above results, graphene oxide and Li 0.375 Sr 0.4375 Ta 0.75 Zr 0.25 O3 perovskite solid electrolyte nanoparticles, and both formed a dense and uniform coating on the polyethylene membrane substrate.

[0129] 3. Determination of physical properties of diaphragm

[0130] The liquid absorption rate and heat shrinkage test were performed on Examples 1-13 and Comparative Examples 1-3. The specific process is as follows:

[0131] The liquid absorption rate test includes the following steps: Take a diaphragm sample and weigh it, which is recorded as m1. Place the sample in the electrolyte, seal it and soak it for 1 hour, then take it out, wipe the electrolyte on the surface of the sample with a dust-free cloth, weigh it and record it as m2. Liquid absorption rate = ((m2-m1) / m1)×100%.

[0132] Heat shrinkage test: refer to GB / T 36363-2018. Take a membrane sample with a side length of 28 mm, place it flat on a quantitative filter paper, press it with another quantitative filter paper, place it in a blast thermostatic box, heat it at 105°C for 1 hour, and then take it out. That is, the length before heating is L1, the length after heating is L2, and the shrinkage rate after heating S = ((L1-L2) / L1) × 100%.

[0133] The experimental results are shown in Table 2. Comparative analysis shows that the liquid absorption rate of the diaphragms coated with graphene oxide and perovskite solid electrolyte slurry in Examples 1-13 is significantly increased. It shows that the above-mentioned modified coating can effectively improve the electrolyte affinity of commercial polyethylene diaphragms. Compared with the diaphragm substrate described in Comparative Example 1 and the diaphragms coated with only one of the materials of graphene oxide or perovskite solid electrolyte in Comparative Examples 2-3, the thermal shrinkage of the diaphragm coated with a suitable proportion of graphene oxide and perovskite solid electrolyte in the embodiment after heating at 130°C for 1 hour is significantly reduced, indicating that the modified coating also has a positive effect on the high temperature stability of commercial polyethylene diaphragms.

[0134] Table 2

[0135]

[0136] 4. Electrochemical analysis

[0137] The separators prepared in Examples 1-13 and Comparative Examples 1-3 were respectively assembled into Li||Li symmetrical batteries, and the electrochemical performance was tested.

[0138] The metal lithium sheet was cut into discs with a diameter of 1 cm as the positive and negative electrodes of the battery. Using an electrolyte (a mixed solvent of ethylene glycol carbonate (EC) and diethylene glycol carbonate (DEC) with a volume ratio of 1:1, containing 1.0M LiPF6 and 10wt% fluoroethylene carbonate (FEC)), a stainless steel 2032 button battery shell and accessories, the diaphragms of Examples 1-15 and Comparative Examples 1-3 were assembled into 2032 button batteries under an argon atmosphere. Using a Xinwei multi-channel battery tester (BTS-600), at 1mA / cm 2 The surface current density and 1 mAh / cm 2 The lithium insertion and extraction behavior of Li∥Li symmetric battery was tested at the surface capacity.

[0139] The experimental results are shown in Table 3. Comparative analysis shows that the diaphragm coated with a mixed slurry of graphene oxide and perovskite solid electrolyte in an appropriate ratio in the embodiment significantly reduces the overpotential of the symmetrical battery after the same cycle time, compared with the diaphragm substrate described in Comparative Example 1 and the diaphragms coated with only one of the materials of graphene oxide or perovskite solid electrolyte in Comparative Examples 2-3.

[0140] The charge and discharge time-voltage curves of the Li / Li symmetrical batteries of Example 1 and Comparative Example 1 are shown in FIG. Figure 4 As shown. The initial polarization and activation time of the button battery assembled using the diaphragm of Example 1 are significantly shorter than those of the button battery assembled using the diaphragm substrate of Comparative Example 1. The overpotential of the button battery assembled using the diaphragm substrate of Comparative Example 1 increased significantly after about 250 hours of charge and discharge cycles; after about 280 hours of cycling, an overpotential of about 41 mV was observed. In comparison, the overpotential of the button battery assembled using the diaphragm of Example 1 was less than 25 mV even after more than 400 hours of cycling. The above results indicate that providing a coating composed of graphene oxide and perovskite solid electrolyte on a commercial polyethylene diaphragm can effectively reduce polarization and improve electrochemical stability.

[0141] Table 3

[0142]

[0143]

[0144] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A diaphragm, characterized in that: include: A porous base membrane and a coating, wherein the coating is disposed on at least one surface of the porous base membrane; The coating comprises graphene oxide and a perovskite-type solid electrolyte.

2. The diaphragm according to claim 1, characterized in that The mass ratio of the graphene oxide to the perovskite-type solid electrolyte is 1:(1-3).

3. The diaphragm according to claim 1, characterized in that The coating has a thickness of 0.01 μm-5 μm.

4. The diaphragm according to claim 2, characterized in that The molecular formula of the perovskite solid electrolyte is Li 2x- y Sr 1-x Ta y Zr 1-y O3, where 0.60≤y≤0.75, x=0.75y.

5. The diaphragm according to claim 4, characterized in that The particle size of the perovskite solid electrolyte is 0.02 μm-10 μm.

6. The diaphragm according to claim 1, characterized in that The thickness of the porous base film is 5 μm-20 μm; And / or, the porosity of the porous base film is 30% to 50%; And / or, the pore size of the porous base membrane is 0.01 μm-0.3 μm.

7. The diaphragm according to claim 6, characterized in that The porous base film includes at least one of polyethylene film, polypropylene film, polyimide film, polyethylene terephthalate film, polyvinylidene fluoride film, polyvinylidene fluoride-hexafluoropropylene copolymer film, polyetheretherketone film, polymethyl methacrylate film, polyetherimide film, polyaramid film and cellulose film.

8. A method for preparing the diaphragm according to any one of claims 1 to 7, characterized in that: include: loading a slurry containing graphene oxide and a perovskite-type solid electrolyte on at least one surface of the porous base film to form a coating; The porous base film having the coating layer is dried to obtain the separator.

9. The method according to claim 8, characterized in that The slurry further includes a solvent and a binder.

10. The method according to claim 9, characterized in that The mass ratio of the solvent, the binder, the graphene oxide and the perovskite-type solid electrolyte is 100:(0.05-0.1):(0.05-0.5):(0.05-1.5).

11. The method according to claim 8, characterized in that The drying process is carried out at 35° C.-45° C. for 10 h-15 h.

12. A battery, characterized in that: The invention comprises the diaphragm described in any one of claims 1 to 7 or the diaphragm prepared by the method described in any one of claims 8 to 11.

13. An electrical device, characterized in that: Comprising the battery as claimed in claim 12.

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