Diaphragm and preparation method thereof, battery monomer, battery and electric device

Abstract

The invention discloses a diaphragm and a preparation method thereof, a battery monomer, a battery and a power utilization device, the diaphragm comprises a graphene oxide layer, and a first porous base material layer and a second porous base material layer located at two sides of the graphene oxide layer, the graphene oxide layer comprises a porous graphene oxide microchip, the transverse size of the porous graphene oxide microchip is 0.5 mu m-3 mu m, and the porosity of the porous graphene oxide microchip is 10%-30%. The diaphragm disclosed by the invention has high mechanical strength, high thermal stability, high air permeability and high ion conduction capability, and also has the effects of digesting dendritic crystals and reducing the risk of short circuit in a battery monomer caused by contact between the dendritic crystals piercing the diaphragm and a positive electrode.

Description

Technical Field

[0001] The present application relates to a diaphragm and a preparation method thereof, a battery cell, a battery and an electrical device. Background Art

[0002] With the application and promotion of batteries, their reliability and service life are receiving increasing attention. During the battery charging and discharging process, the problem of dendrites on the negative electrode is one of the major factors affecting battery reliability and service life. How to slow down the growth of dendrites without affecting the electrochemical performance of the battery is a technical problem that needs to be solved urgently. Summary of the Invention

[0003] The present application provides a diaphragm and a preparation method thereof, a battery cell, a battery and an electrical device. The diaphragm has high mechanical strength, high thermal stability, high air permeability and high ion conductivity, and has the function of dissolving dendrites and reducing the risk of dendrites piercing the diaphragm and contacting the positive electrode, causing internal short circuit in the battery cell.

[0004] In a first aspect, the present application provides a diaphragm, comprising a graphene oxide layer and a first porous substrate layer and a second porous substrate layer located on both sides of the graphene oxide layer, the graphene oxide layer comprising porous graphene oxide microsheets, the lateral dimensions of the porous graphene oxide microsheets being 0.5 μm-3 μm, and the porosity of the porous graphene oxide microsheets being 10%-30%.

[0005] The diaphragm includes a graphene oxide layer and a first porous substrate layer and a second porous substrate layer located on both sides of the graphene oxide layer. The structure of this diaphragm is more stable, and the graphene oxide layer can be prevented from directly contacting the positive and negative electrodes, thereby improving the capacity and cycle performance of the battery cell. By adopting porous graphene oxide microsheets with a porous structure as an intermediate layer, the permeability of the diaphragm can be effectively improved, the ion conductivity of the diaphragm can be improved, and the internal resistance of the battery cell can be reduced. By adjusting the lateral size and porosity of the porous graphene oxide microsheets within the above range, the diaphragm can have high mechanical strength, high thermal stability, high permeability and high ion conductivity. Therefore, the diaphragm provided in the embodiment of the present application has high mechanical strength, high thermal stability, high permeability and high ion conductivity, and has the effect of dissolving dendrites, reducing the risk of dendrites piercing the diaphragm and contacting the positive electrode to cause internal short circuit of the battery cell, and thus can make the battery cell have high reliability, good cycle performance and rate performance.

[0006] In some embodiments, the lateral dimensions of the porous graphene oxide microsheets are 0.5 μm to 1.5 μm; and / or the porosity of the porous graphene oxide microsheets is 16% to 25%. By further adjusting the lateral dimensions of the porous graphene oxide microsheets, the separator can better combine high mechanical strength, high thermal stability, high gas permeability, and high ion conductivity, thereby improving the cycle performance and rate performance of the battery cell. By further adjusting the porosity of the porous graphene oxide microsheets, the separator can better combine high mechanical strength, high thermal stability, high gas permeability, and high ion conductivity, thereby improving the cycle performance and rate performance of the battery cell.

[0007] In some embodiments, the average pore size of the porous graphene oxide microsheets is 1.5 nm to 10 nm, optionally 2 nm to 8 nm. By further adjusting the average pore size of the porous graphene oxide microsheets, the separator can better combine high mechanical strength, high thermal stability, high gas permeability, and high ion conductivity, thereby improving the cycle performance and rate performance of the battery cell.

[0008] In some embodiments, the area of ​​pores with a pore size greater than 2 nm in the porous graphene oxide microsheets accounts for more than 60% of the total pore area. Alternatively, the area of ​​pores with a pore size greater than 2 nm in the porous graphene oxide microsheets accounts for 80%-92% of the total pore area. By further adjusting the pore size distribution of the porous graphene oxide microsheets, the separator can better combine high mechanical strength, high thermal stability, high permeability, and high ion conductivity, thereby improving the cycle performance and rate performance of the battery cell.

[0009] In some embodiments, the specific surface area of ​​the porous graphene oxide microsheet is 50m 2 / g-500m 2 By further adjusting the specific surface area of ​​porous graphene oxide microsheets, the separator can better combine high mechanical strength, high thermal stability, high gas permeability and high ion conductivity, which is beneficial to improving the cycle performance and rate performance of battery cells.

[0010] In some embodiments, the mass proportion of oxygen in the porous graphene oxide microsheets is 15%-35%.

[0011] In some embodiments, the porous graphene oxide microsheet includes doping elements, and the doping elements include one or more of fluorine, nitrogen, sulfur, and phosphorus; and / or the mass proportion of the doping elements in the porous graphene oxide microsheet is 1%-15%.

[0012] In some embodiments, the porous graphene oxide microsheets have a thickness of 1 nm to 2 nm.

[0013] In some embodiments, the mass fraction of the porous graphene oxide microplatelets in the graphene oxide layer is greater than or equal to 50%, and optionally greater than or equal to 70%. By ensuring that the content of the porous graphene oxide microplatelets in the graphene oxide layer is within the above range, the ion conductivity of the separator is improved while enabling the separator to better dissipate dendrites growing on the negative electrode.

[0014] In some embodiments, the graphene oxide layer further includes inorganic nanoparticles having a volume distribution particle size (Dv50) of 30 nm to 500 nm. The inclusion of inorganic nanoparticles in the graphene oxide layer can act as spacing between the porous graphene oxide microsheets, thereby further improving the permeability of the separator. Furthermore, the gaps between the stacked porous graphene oxide microsheets allow ions to pass more easily, further improving the ion conductivity of the separator.

[0015] In some embodiments, the mass proportion of inorganic nanoparticles in the graphene oxide layer is less than or equal to 40%.

[0016] In some embodiments, the inorganic nanoparticles include one or more of ceramic and solid electrolyte particles.

[0017] In some embodiments, the graphene oxide layer has a thickness of 0.5 μm to 5 μm. A thickness within this range can provide a high content of porous graphene oxide microsheets to eliminate dendrites growing on the negative electrode while also preventing excessive porous graphene oxide microsheets from consuming excessive active material and reducing the capacity of the battery cell.

[0018] In some embodiments, the graphene oxide layer further includes a binder and a wetting agent.

[0019] In some embodiments, the thickness of the first porous substrate layer is 3 μm-14 μm.

[0020] In some embodiments, the porosity of the first porous substrate layer is 40% to 80%.

[0021] In some embodiments, the first porous substrate layer includes one or more of polyolefins, polyamides, polyesters, and derivatives thereof.

[0022] In some embodiments, the second porous substrate layer has a thickness of 3 μm to 14 μm.

[0023] In some embodiments, the porosity of the second porous substrate layer is 40% to 80%.

[0024] In some embodiments, the second porous substrate layer includes two or more of polyolefins, polyamides, polyesters, and their derivatives.

[0025] In some embodiments, the total thickness of the separator is 7 μm-30 μm.

[0026] In some embodiments, the membrane has a porosity of 30% to 80%.

[0027] In a second aspect, the present application provides a method for preparing a diaphragm, which is used to prepare the diaphragm of the first aspect of the present application, comprising the following steps: providing a first porous substrate layer, a second porous substrate layer, and a slurry containing porous graphene oxide microsheets, wherein the lateral size of the porous graphene oxide microsheets is 0.5 μm-3 μm, and the porosity of the porous graphene oxide microsheets is 10%-30%; coating the slurry on one surface of the first porous substrate layer and / or one surface of the second porous substrate layer, and then stacking and compounding the first porous substrate layer and the second porous substrate layer together to form a diaphragm, wherein the diaphragm includes a graphene oxide layer and the first porous substrate layer and the second porous substrate layer located on both sides of the graphene oxide layer.

[0028] In some embodiments, the method for preparing the porous graphene oxide microsheets includes the following steps: providing graphene oxide, wherein the graphene oxide is in the form of flakes; uniformly dispersing the graphene oxide with water to obtain a graphene oxide dispersion; mixing the obtained graphene oxide dispersion with a pore-forming agent, stirring and reacting for a period of time, and then performing solid-liquid separation to obtain a precipitate; and drying and grinding the obtained precipitate to obtain porous graphene oxide microsheet powder.

[0029] Optionally, the mass fraction of the graphene oxide dispersion is 0.1%-10%.

[0030] Optionally, the pore-forming agent is hydrogen peroxide, and the mass fraction of the hydrogen peroxide is 20%-40%.

[0031] Optionally, the volume ratio of the pore-forming agent to the graphene oxide dispersion is 1:(5-50).

[0032] Optionally, the obtained graphene oxide dispersion is mixed with a pore-forming agent, and the stirring reaction temperature is 80° C.-120° C.

[0033] Optionally, the obtained graphene oxide dispersion is mixed with a pore-forming agent, and the stirring reaction time is 1 hour to 4 hours.

[0034] In other embodiments, the method for preparing the porous graphene oxide microsheets includes the following steps: providing graphene oxide, wherein the graphene oxide is in the form of flakes; uniformly dispersing the graphene oxide with water to obtain a graphene oxide dispersion; adding thiourea to the obtained graphene oxide dispersion and heating it in a reactor, and finally performing vacuum freeze-drying to obtain porous graphene oxide microsheet powder.

[0035] Optionally, the mass fraction of the graphene oxide dispersion is 0.1%-10%.

[0036] Optionally, the mass ratio of the thiourea to the graphene oxide dispersion is 1:(50-550).

[0037] Optionally, thiourea is added to the obtained graphene oxide dispersion and heated in a reactor at a temperature of 150° C. to 200° C.

[0038] Optionally, thiourea is added to the obtained graphene oxide dispersion and heated in a reactor for 4 h to 5 h.

[0039] Optionally, the temperature of the vacuum freeze-drying treatment is -50°C to -80°C.

[0040] Optionally, the vacuum freeze-drying treatment time is 1 hour to 2 hours.

[0041] Optionally, the vacuum degree of the vacuum freeze-drying process is 85KPa-95KPa.

[0042] In a third aspect, the present application provides a battery cell, comprising the diaphragm according to the first aspect of the present application or the diaphragm prepared by the preparation method according to the second aspect of the present application.

[0043] In a fourth aspect, the present application provides a battery comprising the battery cell according to the third aspect of the present application.

[0044] In a fifth aspect, the present application provides an electrical device comprising the battery according to the fourth aspect of the present application, wherein the battery is used to provide electrical energy.

[0045] The electric device of the present application includes the battery provided by the present application, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0047] Figure 1 A schematic diagram showing a battery cell provided by some embodiments of the present application.

[0048] Figure 2 A schematic diagram of an exploded view of a battery cell provided by some embodiments of the present application is shown.

[0049] Figure 3 A schematic diagram of a battery module provided in some embodiments of the present application is shown.

[0050] Figure 4 A schematic diagram of a battery pack provided in some embodiments of the present application is shown.

[0051] Figure 5 yes Figure 4 Schematic diagram of the battery pack shown.

[0052] Figure 6 A schematic diagram of an electrical device provided in some embodiments of the present application is shown.

[0053] Figure 7 This is a scanning electron microscope (SEM) image of the porous graphene oxide microsheets prepared in Example 1.

[0054] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0055] The description of the accompanying figures is as follows: 1. battery pack; 2. upper box; 3. lower box; 4. battery module; 5. battery cell; 51. shell; 52. electrode assembly; 53. cover plate. DETAILED DESCRIPTION

[0056] Below, the embodiments of the diaphragm and its preparation method, battery cell, battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0057] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0058] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0059] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0060] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0061] In this application, the terms "plurality" and "multiple" refer to two or more.

[0062] In the description of the embodiments of the present application, unless otherwise specified, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "below," "below," and "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0063] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0064] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0065] Unless otherwise specified, the test instruments mentioned in this application can be operated in accordance with the requirements of the product specifications.

[0066] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module, or a battery pack.

[0067] A battery cell is the smallest unit that makes up a battery and can independently realize the function of charging and discharging. A battery cell can be cylindrical, rectangular or other shapes, etc., which is not limited in the embodiments of the present application. Figure 1 As an example, a battery cell 5 having a rectangular parallelepiped structure is shown.

[0068] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in mixed series via a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed in the housing. In some embodiments, the housing may serve as part of the vehicle's chassis structure. For example, a portion of the housing may form at least a portion of the vehicle's floor, or a portion of the housing may form at least a portion of the vehicle's crossbeam or longitudinal beam.

[0069] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0070] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly can be a wound structure or a laminated structure, which is not limited in the present embodiment.

[0071] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode assembly and electrolyte. The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging can also be a soft package, such as a pouch-type soft package. The soft package can be made of plastic, such as one or more of polypropylene, polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0072] In some embodiments, as Figure 2 As shown, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, which together form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening, thereby sealing the receiving cavity. The electrode assembly 52 is enclosed in the receiving cavity. The number of electrode assemblies 52 contained in a battery cell 5 can be one or more, and can be adjusted according to needs.

[0073] In some embodiments, battery cells may be assembled into a battery module. A battery module may contain multiple battery cells, and the specific number may be adjusted according to the application and capacity of the battery module. Figure 3 FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 3 As shown, in the battery module 4, the plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0074] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0075] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0076] Figure 4 and Figure 5 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 4 and Figure 5 As shown, a battery pack 1 may include a housing and multiple battery modules 4 disposed therein. The housing comprises an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the housing.

[0077] The battery cells provided in the embodiments of the present application may be metal battery cells, for example, they may include lithium metal battery cells, negative electrode-free lithium metal battery cells, sodium metal battery cells, negative electrode-free sodium metal battery cells, etc.

[0078] A negative electrode-free battery cell generally refers to a battery cell constructed without a negative electrode active material layer applied to the negative electrode during the manufacturing process. For example, a carbonaceous active material layer is not applied to the negative electrode via coating or deposition. During initial charging, ions on the negative electrode gain electrons and deposit on the surface of the negative electrode current collector to form metal. During discharge, the metal converts to ions and returns to the positive electrode, enabling cyclic charge and discharge. Compared to other battery cells, the absence of a negative electrode active material layer allows negative electrode-free battery cells to achieve higher energy density. In some embodiments, to improve battery cell performance, the negative electrode of a negative electrode-free battery cell may also contain conventional negative electrode active materials, such as carbon materials. Although these materials have a certain capacity, their low content and their non-primary negative electrode active material role in the battery cell still qualify as a negative electrode-free battery cell. The cell balance (CB) value of a negative electrode-free battery cell is typically very low. For example, in some embodiments, the CB value of a negative electrode-free battery cell can be less than or equal to 0.1. The CB value is the unit area capacity of the negative electrode in a battery cell divided by the unit area capacity of the positive electrode. Since a battery cell without a negative electrode contains no or only a small amount of negative electrode active material, the unit area capacity of the negative electrode is small, and thus the CB value is very small, for example, usually less than or equal to 0.1.

[0079] A battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet.

[0080] The negative electrodes of battery cells, especially metal battery cells, usually have serious dendrite problems. The presence of dendrites will shorten the life of the battery cells and affect the use of the battery cells. In particular, after the battery cells are charged and discharged for a long time and at a high rate, the negative electrodes are more likely to grow dendrites, resulting in poor cycle performance of the battery cells.

[0081] Graphene oxide (GO) is rich in oxygen-containing functional groups, such as hydroxyl (-OH), carboxyl (-COOH), and aldehyde (-CHO). These oxygen-containing functional groups can react with metals such as lithium and sodium to form metal oxides such as lithium oxide and sodium oxide, as well as reduced graphene oxide (rGO). Therefore, when applied to separators, GO can help dissipate dendrites growing on the negative electrode. For example, the reaction between GO and lithium dendrites is as follows: GO + Li → rGO + Li₂O. Graphene oxide is rich in oxygen-containing functional groups, such as hydroxyl (-OH), carboxyl (-COOH), and aldehyde (-CHO). This can improve the compatibility of the separator with the electrolyte, enhancing its wettability and electrolyte retention. Graphene oxide has high mechanical strength and good heat resistance, resisting dendrite penetration and thermal shrinkage of the porous substrate layer caused by internal temperature rise in the battery cell, thereby imparting high mechanical strength and good heat resistance to the separator.

[0082] Graphene oxide has many advantages and can be used in separators to dissolve dendrites. However, flaky graphene oxide easily swells in solvents and easily stacks when coated on a porous substrate, leading to ion channel blockage, poor permeability and ion conductivity of the separator, and a significant increase in the internal resistance of the battery cell. This affects its dendrite dissolving effect, as well as the cycle and rate performance of the battery cell, especially the performance of the battery cell after long-term, high-rate charge and discharge.

[0083] The present application starts from the structure of the diaphragm, by arranging a graphene oxide layer including porous graphene oxide microsheets between two porous substrate layers, and using the diaphragm in metal battery cells, such as lithium metal battery cells, negative electrode-free lithium metal battery cells, sodium metal battery cells, negative electrode-free sodium metal battery cells, etc., so that the battery cells can have high reliability, good cycle performance and rate performance.

[0084] The diaphragm provided in the embodiment of the present application includes a graphene oxide layer and a first porous substrate layer and a second porous substrate layer located on both sides of the graphene oxide layer. The graphene oxide layer includes porous graphene oxide microsheets. The lateral size of the porous graphene oxide microsheets is 0.5μm-3μm, and the porosity of the porous graphene oxide microsheets is 10%-30%.

[0085] The separator provided in the embodiments of the present application has a multilayer structure, comprising a graphene oxide layer and a first porous substrate layer and a second porous substrate layer located on either side of the graphene oxide layer. This separator structure is more stable and prevents direct contact between the graphene oxide layer and the positive and negative electrodes, thereby improving the capacity and cycle performance of the battery cells. This is because the side reactions caused by the contact between the graphene oxide and the positive and negative electrodes consume active materials, reducing the capacity and cycle life of the battery cells.

[0086] The graphene oxide layer includes porous graphene oxide microsheets. By using porous graphene oxide microsheets with a porous structure as the intermediate layer, the permeability of the separator can be effectively improved, the ion conductivity of the separator can be improved, and the internal resistance of the battery cell can be reduced.

[0087] The porous graphene oxide microsheets have a lateral dimension of 0.5 μm to 3 μm and a porosity of 10% to 30%. By adjusting the lateral dimension and porosity of the porous graphene oxide microsheets within these ranges, the separator can be made to have high mechanical strength, high thermal stability, high gas permeability, and high ion conductivity.

[0088] Overly large porous graphene oxide microsheets will increase the difficulty of preparing graphene oxide layer slurry. The larger the size, the worse the stirring property of the slurry. After coating, the surface of the film layer will have obvious granularity, resulting in poor coating quality. In addition, overly large porous graphene oxide microsheets will be more likely to stack on each other and cause pore blocking problems after swelling in the electrolyte, thereby reducing the ion conductivity of the diaphragm and affecting the performance of the battery cell.

[0089] Porous graphene oxide microsheets that are too small can easily fall into the pores of the porous substrate layer, causing pore blockage in the separator and affecting the performance of the battery cell.

[0090] The porosity of porous graphene oxide microsheets is too high, their own mechanical strength deteriorates, and the risk of pulverization increases, which can easily cause pore blockage in the diaphragm and affect the performance of the battery cell after multiple cycles of charge and discharge.

[0091] The porosity of porous graphene oxide microsheets is too small, and the ion conductivity of the diaphragm is poor.

[0092] Therefore, the diaphragm provided in the embodiments of the present application has not only high mechanical strength, high thermal stability, high air permeability and high ion conductivity, but also has the function of dissolving dendrites and reducing the risk of dendrites piercing the diaphragm and contacting the positive electrode to cause internal short circuit of the battery cell, thereby making the battery cell have high reliability, good cycle performance and rate performance.

[0093] It should be noted that in this application, the terms graphene oxide and porous graphene oxide microsheets can be understood with reference to the meanings in GB / T 30544.13-2018, and the relevant parameters can also be measured with reference to this standard.

[0094] The lateral size of the porous graphene oxide microplatelet is 0.5 μm-3 μm, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, or a range consisting of any of the above values. Optionally, the lateral size of the porous graphene oxide microplatelet can be 0.5 μm-1.5 μm.

[0095] By further adjusting the lateral dimensions of the porous graphene oxide microsheets, the separator can better combine high mechanical strength, high thermal stability, high permeability and high ion conductivity, which is beneficial to improving the cycle performance and rate performance of the battery cell.

[0096] The lateral dimensions of porous graphene oxide microsheets can be tested as follows: a graphene oxide layer is immersed in a solvent, N-methylpyrrolidone (NMP), stirred thoroughly, centrifuged, and dried to obtain porous graphene oxide, and its lateral dimensions are observed and resolved using a scanning electron microscope.

[0097] The porosity of the porous graphene oxide microplatelets is 10%-30%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or any range thereof. Alternatively, the porosity of the porous graphene oxide microplatelets may be 16%-25%, 17%-25%, 18%-25%, 19%-25%, or 20%-25%.

[0098] By further adjusting the porosity of porous graphene oxide microsheets, the separator can better combine high mechanical strength, high thermal stability, high permeability and high ion conductivity, which is beneficial to improving the cycle performance and rate performance of battery cells.

[0099] In some embodiments, the average pore size of the porous graphene oxide microplatelets can be 1.5 nm to 10 nm, for example, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any range thereof. Alternatively, the average pore size of the porous graphene oxide microplatelets can be 2 nm to 8 nm, 2.5 nm to 7 nm, 2.5 nm to 6 nm, or 3 nm to 6 nm.

[0100] By further adjusting the average pore size of the porous graphene oxide microsheets, the separator can better combine high mechanical strength, high thermal stability, high permeability and high ion conductivity, which is beneficial to improving the cycle performance and rate performance of the battery cell.

[0101] In some embodiments, the area of ​​pores with a pore diameter greater than 2 nm in the porous graphene oxide microsheet can account for more than 60% of the total pore area, which is the ratio of the sum of the areas of all pores with a pore diameter greater than 2 nm in the porous graphene oxide microsheet to the sum of the areas of all pores in the porous graphene oxide microsheet (i.e., the total pore area).

[0102] Optionally, the area of ​​pores with a pore diameter greater than 2 nm in the porous graphene oxide microplatelet may account for more than 70%, more than 75%, or more than 80% of the total pore area. More preferably, the area of ​​pores with a pore diameter greater than 2 nm in the porous graphene oxide microplatelet may account for 80%-92%, 82%-92%, 84%-92%, 85%-92%, 82%-90%, 84%-90%, 85%-90%, 82%-88%, 84%-88%, or 85%-88% of the total pore area.

[0103] By further adjusting the pore size distribution of porous graphene oxide microsheets, the separator can better combine high mechanical strength, high thermal stability, high permeability and high ion conductivity, which is beneficial to improving the cycle performance and rate performance of battery cells.

[0104] In some embodiments, the specific surface area of ​​the porous graphene oxide microsheets can be 50 m 2 / g-500m 2 / g.

[0105] By further adjusting the specific surface area of ​​porous graphene oxide microsheets, the separator can better combine high mechanical strength, high thermal stability, high permeability and high ion conductivity, which is beneficial to improving the cycle performance and rate performance of battery cells.

[0106] The specific surface area, average pore size, pore size distribution, and porosity of porous graphene oxide microsheets can be measured as follows: the graphene oxide layer is immersed in N-methylpyrrolidone (NMP) solvent, stirred thoroughly, centrifuged, and dried to obtain porous graphene oxide. The surface area is then measured using nitrogen adsorption specific surface area analysis according to GB / T 19587-2017 and calculated using the Brunauer Emmett Teller (BET) method. The test instrument can be a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0107] In some embodiments, the mass proportion of oxygen in the porous graphene oxide microsheets may be 15%-35%.

[0108] The higher the oxygen content in the porous graphene oxide microsheets, the higher the degree of oxidation, and the higher the content of hydrophilic oxygen-containing functional groups such as hydroxyl (-OH), carboxyl (-COOH), and aldehyde (-CHO), which is beneficial to improving the electrolyte wettability of the diaphragm.

[0109] The higher the oxygen content in the porous graphene oxide microsheets, the better their electronic insulation, and the lower the risk of leakage current caused by electrons passing through the diaphragm. In addition, the risk of side reactions in the porous graphene oxide microsheets through electron transfer is reduced, and the stability of the porous graphene oxide microsheets is improved.

[0110] In some embodiments, the porous graphene oxide microplatelets may further include doping elements. The doping elements may improve the charge distribution on the surface of the porous graphene oxide microplatelets, thereby accelerating charge transfer.

[0111] Optionally, the doping elements include one or more of fluorine, nitrogen, sulfur, and phosphorus.

[0112] Optionally, the mass proportion of the doping element in the porous graphene oxide microsheet may be 1%-15%, 1%-10%, 1%-8%, or 1%-5%.

[0113] The contents of oxygen and doping elements in porous graphene oxide microsheets can be tested by energy dispersive X-ray spectroscopy (EDS).

[0114] In some embodiments, the porous graphene oxide microplatelets may have a thickness of 1 nm to 2 nm.

[0115] In some embodiments, the mass fraction of the porous graphene oxide microplatelets in the graphene oxide layer may be greater than or equal to 50%, for example, greater than or equal to 55%, greater than or equal to 60%, greater than or equal to 65%, greater than or equal to 70%, greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, or greater than or equal to 90%. Alternatively, the mass fraction of the porous graphene oxide microplatelets in the graphene oxide layer may be 50%-97.5%, 60%-97.5%, 65%-97.5%, 70%-97.5%, 75%-97.5%, 80%-97.5%, 85%-97.5%, 70%-95%, 75%-95%, 80%-95%, 85%-95%, 70%-90%, 75%-90%, 80%-90%, or 85%-90%.

[0116] By ensuring that the content of the porous graphene oxide microsheets in the graphene oxide layer is within the above range, it is beneficial to improve the ion conductivity of the separator while enabling the separator to better dissipate dendrites grown on the negative electrode.

[0117] In some embodiments, the graphene oxide layer may have a thickness of 0.5 μm to 5 μm, for example, 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 any range thereof. Alternatively, the graphene oxide layer may have a thickness of 1 μm to 4 μm.

[0118] The porous graphene oxide microsheets can dissolve the dendrites growing on the negative electrode when the battery cell is charged and discharged, and at the same time consume a portion of the active material. The thickness of the graphene oxide layer is within the above range, which can not only provide a high content of porous graphene oxide microsheets to dissolve the dendrites growing on the negative electrode, but also avoid excessively high content of porous graphene oxide microsheets that consume too much active material and reduce the capacity of the battery cell.

[0119] Porous graphene oxide microsheets are rich in oxygen-containing functional groups such as hydroxyl (-OH), carboxyl (-COOH), and aldehyde (-CHO), which can improve the compatibility between the separator and the electrolyte. The thickness of the graphene oxide layer is within the above range, which is also beneficial to improving the separator's wetting and liquid retention properties for the electrolyte, and thus is beneficial to the battery cell having good cycle performance and rate performance.

[0120] When the thickness of the graphene oxide layer is within the above range, the separator also has a relatively small internal resistance, which is beneficial for the battery cell to have good cycle performance and rate performance.

[0121] In some embodiments, the graphene oxide layer may further include inorganic nanoparticles.

[0122] By making the graphene oxide layer further include inorganic nanoparticles, it can play the role of spacing the porous graphene oxide microsheets, thereby further improving the permeability of the membrane. At the same time, the gaps between the stacked porous graphene oxide microsheets can allow ions to pass through better, thereby further improving the ion conductivity of the membrane.

[0123] Inorganic nanoparticles have high mechanical strength and good heat resistance, which can make the separator have better mechanical strength and heat resistance, and can also reduce the risk of dendrites piercing the separator and contacting the positive electrode, causing internal short circuit in the battery cell.

[0124] In some embodiments, the volume distribution particle size Dv50 of the inorganic nanoparticles may be 30 nm-500 nm, optionally 50 nm-300 nm.

[0125] By adjusting the volume distribution particle size Dv50 of the inorganic nanoparticles in the graphene oxide layer within the above range, the air permeability of the separator can be better improved, and the ion conduction capability of the separator can be improved.

[0126] The volume distribution particle size (Dv50) of inorganic nanoparticles is well known in the art and can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer (such as the Malvern Mastersizer 3000) in accordance with GB / T 19077-2016. The physical definition of Dv50 is the particle size corresponding to the 50% cumulative volume distribution percentage of a material.

[0127] In some embodiments, the mass proportion of inorganic nanoparticles in the graphene oxide layer may be less than or equal to 40%, for example, less than or equal to 30%, less than or equal to 25%, less than or equal to 20%, less than or equal to 15%, or less than or equal to 10%.

[0128] By making the content of inorganic nanoparticles in the graphene oxide layer within the above range, the air permeability of the separator can be better improved, the ion conductivity of the separator can be improved, and the separator can also have better mechanical strength, puncture resistance and heat resistance.

[0129] In some embodiments, the inorganic nanoparticles may include one or more of ceramics and solid electrolyte particles.

[0130] Alternatively, the ceramic may include, but is not limited to, one or more of boehmite, silicon oxide, titanium oxide, aluminum oxide, zinc oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, mica, bentonite, hectorite, kaolin, and talc.

[0131] Alternatively, the solid electrolyte particles may include an inorganic solid electrolyte.

[0132] Optionally, the ionic conductivity of the inorganic solid electrolyte may be greater than or equal to 10 -6 S / cm, can be selected to be greater than or equal to 10 -4 S / cm, 10 is optional -4 S / cm-10S / cm.

[0133] Alternatively, the inorganic solid electrolyte may include one or more of an oxide-type inorganic solid electrolyte, a sulfide-type inorganic solid electrolyte, and a halide-type inorganic solid electrolyte.

[0134] Optionally, the oxide-type inorganic solid electrolyte may include one or more of a NASICON-type solid electrolyte and a LISICON-type solid electrolyte.

[0135] Optionally, the sulfide-based inorganic solid electrolyte may include one or more of a sulfide-based crystalline solid electrolyte and a sulfide glass-based solid electrolyte.

[0136] As an example, the inorganic solid electrolyte may include lithium titanium phosphate Li x Ti y (PO4)3 (0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate Li x Al y Ti z (PO4)3 (abbreviated as LATP, 0 < x < 2, 0 < y < 1, 0 < z < 3), lithium aluminum germanium phosphate Li x Al y Ge z (PO4)3 (abbreviated as LAGP, 0 < x < 2, 0 < y < 1, 0 < z < 3), lithium aluminum zirconium phosphate Li x Al y Zr z (PO4)3 (abbreviated as LAZP, 0 < x < 2, 0 < y < 1, 0 < z < 3), lithium aluminum chromium phosphate Li x Al y Cr z (PO4)3 (abbreviated as LACP, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP)<00​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​12 , Li6PS5Cl, Li6PS5Br, and one or more of their respective dopant compounds. Dopant compounds are typically obtained by doping a compound with another element, such as a metal element. The type of dopant element is not particularly limited, as long as it does not detract from the subject matter of this application.

[0137] As an example, lithium titanium phosphate Li x Ti y (PO4)3 may include LiTi2(PO4)3. As an example, lithium aluminum titanium phosphate Li x Al y Ti z (PO4)3 can include Li 1.3 Al 0.3 Ti 1.7 (PO4)3. As an example, lithium germanium aluminum phosphate may include Li 1.5 A1 0.5 Ge 1.5 (PO4)3.

[0138] The solid electrolyte particles have good ion conductivity and electronic insulation, and are also highly reactive and can dissolve dendrites.

[0139] In some embodiments, the graphene oxide layer further includes a binder.

[0140] Alternatively, the binder may include, but is not limited to, one or more of vinylidene fluoride polymers, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), poly(meth)acrylic acid, pre-lithiated poly(meth)acrylic acid, and pre-sodiumized poly(meth)acrylic acid. Vinylidene fluoride polymers may include, but are not limited to, one or more of polyvinylidene fluoride (PVDF), vinylidene fluoride-tetrafluoroethylene-propylene terpolymers, and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymers.

[0141] Optionally, based on 100 parts by weight of the total amount of porous graphene oxide microsheets and inorganic nanoparticles, the amount of the binder can be 1-50 parts by weight, optionally 1.5-40 parts by weight, 1.5-30 parts by weight, 1.5-20 parts by weight, 1.5-15 parts by weight, or 1.5-10 parts by weight.

[0142] An appropriate amount of binder can make the porous graphene oxide microsheets and inorganic nanoparticles better adhere to the first porous substrate layer and / or the second porous substrate layer, reducing the problem of powder loss; it is also beneficial to the preparation of graphene oxide layer slurry, facilitates coating, and improves the coating effect.

[0143] In some embodiments, the graphene oxide layer may further include a wetting agent.

[0144] Alternatively, the wetting agent may include, but is not limited to, one or more of polyvinylpyrrolidone (PVP), anionic surfactants, nonionic surfactants, ethylene oxide adducts, polyether-modified polysiloxane compounds, and acetylenic glycol compounds. Nonionic surfactants may include, but are not limited to, nonionic fluorocarbon polymer compounds.

[0145] Optionally, based on 100 parts by weight of the total amount of the porous graphene oxide microsheets and the inorganic nanoparticles, the amount of the wetting agent may be 1-3 parts by weight.

[0146] An appropriate amount of wetting agent can make the graphene oxide layer slurry evenly dispersed, facilitate coating, and also help improve the coating quality of the graphene oxide layer.

[0147] In some embodiments, the thickness of the first porous substrate layer may be 3 μm to 14 μm, and optionally 5 μm to 12 μm.

[0148] In some embodiments, the porosity of the first porous substrate layer may be 40% to 80%.

[0149] When the thickness and / or porosity of the first porous substrate layer is within the above range, the separator can have good ion conductivity and low impedance.

[0150] In some embodiments, the thickness of the second porous substrate layer may be 3 μm to 14 μm, and optionally 5 μm to 12 μm.

[0151] In some embodiments, the porosity of the second porous substrate layer may be 40% to 80%.

[0152] When the thickness and / or porosity of the second porous substrate layer is within the above range, the separator can have good ion conductivity and low impedance.

[0153] In some embodiments, the first porous substrate layer may include one or more of polyolefins, polyamides, polyesters, and derivatives of each thereof.

[0154] In some embodiments, the second porous substrate layer may include one or more of polyolefins, polyamides, polyesters, and derivatives of each thereof.

[0155] Derivatives usually refer to products derived from the replacement of hydrogen atoms or atomic groups in polymers by other atoms or atomic groups.

[0156] Alternatively, the polyester may include, but is not limited to, one or more of polyethylene terephthalate and polybutylene terephthalate.

[0157] Alternatively, the first porous substrate layer may include one or more polyolefins and their derivatives. Alternatively, the monomers used to form the polyolefin may include, but are not limited to, one or more of ethylene, propylene, tetrafluoroethylene, vinylidene fluoride, and vinyl chloride. Alternatively, the first porous substrate layer may include polyethylene.

[0158] Alternatively, the second porous substrate layer may include one or more polyolefins and their derivatives. Alternatively, the monomers used to form the polyolefin may include, but are not limited to, one or more of ethylene, propylene, tetrafluoroethylene, vinylidene fluoride, and vinyl chloride. Alternatively, the second porous substrate layer may include polyethylene.

[0159] Optionally, the weight average molecular weight of the polymer used to prepare the porous substrate layer may be 100,000-1,000,000.

[0160] In some embodiments, the first porous substrate layer may be a single-layer film structure, a multi-layer film structure, or a non-woven fabric structure.

[0161] In some embodiments, the second porous substrate layer may be a single-layer film structure, a multi-layer film structure, or a non-woven fabric structure.

[0162] In some embodiments, the total thickness of the separator may be 7 μm to 30 μm.

[0163] In some embodiments, the porosity of the separator may be 30% to 80%.

[0164] When the total thickness and / or porosity of the separator is within the above range, the separator can have good ion conductivity and low impedance.

[0165] The thicknesses of the first porous substrate layer, the second porous substrate layer, the graphene oxide layer, and the separator have meanings well known in the art and can be measured using methods known in the art. For example, they can be measured with reference to GB / T 6672-2001, Plastics film and sheeting - Determination of thickness - Mechanical measurement method.

[0166] The porosity of the first porous substrate layer, the second porous substrate layer, and the separator has a well-known meaning in the art and can be measured using methods known in the art. For example, the porosity can be measured with reference to GB / T 21650.2-2008, Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Methods - Part 2: Analysis of Mesopores and Macropores by Gas Adsorption Method. The testing equipment can be a Micromeritics AutoPore V 9600 fully automatic mercury intrusion porosimeter.

[0167] [Method for preparing diaphragm]

[0168] The embodiments of the present application also provide a method for preparing a diaphragm, which can prepare the diaphragm provided in the embodiments of the present application.

[0169] The preparation method provided in an embodiment of the present application includes the following steps: providing a first porous substrate layer, a second porous substrate layer and a slurry containing porous graphene oxide microsheets, wherein the lateral size of the porous graphene oxide microsheets is 0.5 μm-3 μm, and the porosity of the porous graphene oxide microsheets is 10%-30%; coating the slurry on one surface of the first porous substrate layer and / or one surface of the second porous substrate layer, and then stacking and compounding the first porous substrate layer and the second porous substrate layer together, and after drying, obtaining a diaphragm, which includes a graphene oxide layer and the first porous substrate layer and the second porous substrate layer located on both sides of the graphene oxide layer.

[0170] In some embodiments, the first porous substrate layer and the second porous substrate layer are laminated together by heat pressing, and the temperature of the heat pressing may be 90° C.-120° C.

[0171] In some embodiments, the first porous substrate layer and the second porous substrate layer are laminated and compounded together by heat pressing, and the pressure of the heat pressing can be 3 MPa-5 MPa.

[0172] In some embodiments, the first porous substrate layer and the second porous substrate layer are laminated and compounded together by heat pressing, and the heat pressing time may be 5 minutes to 15 minutes.

[0173] In some embodiments, the solvent in the slurry containing porous graphene oxide microplatelets may include, but is not limited to, one or more of water, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and dimethyl sulfoxide (DMSO).

[0174] In some embodiments, in the slurry comprising porous graphene oxide microplatelets, the mass ratio of the porous graphene oxide microplatelets to the solvent is (0.5-5):100.

[0175] In some embodiments, the slurry comprising porous graphene oxide platelets may further include a binder and / or a wetting agent.

[0176] In some embodiments, the slurry comprising porous graphene oxide platelets may further include inorganic nanoparticles.

[0177] In some embodiments, the drying temperature of the slurry containing porous graphene oxide platelets may be 60°C to 80°C.

[0178] In some embodiments, the coating method of the slurry containing porous graphene oxide microplatelets may include, but is not limited to, gravure transfer coating, spin spray coating, dip coating, doctor blade coating, and the like.

[0179] In some embodiments, a method for preparing porous graphene oxide microsheets includes the following steps: providing graphene oxide, wherein the graphene oxide is in the form of flakes; uniformly dispersing the graphene oxide with water to obtain a graphene oxide dispersion; mixing the obtained graphene oxide dispersion with a pore-forming agent, stirring and reacting for a period of time, and then performing solid-liquid separation to obtain a precipitate; and drying and grinding the obtained precipitate to obtain porous graphene oxide microsheet powder.

[0180] Traditional pore-forming methods such as phase separation technology are difficult to effectively improve the porosity of porous graphene oxide microsheets. The embodiment of the present application uses a method of reacting a graphene oxide dispersion with a pore-forming agent to form pores, which can obtain porous graphene oxide microsheets with high porosity and uniform average pore size, thereby helping to improve the ion conductivity of the diaphragm.

[0181] Optionally, the mass fraction of the graphene oxide dispersion may be 0.1%-10%.

[0182] Optionally, the graphene oxide and water may be uniformly dispersed by ultrasonic dispersion, and the ultrasonic dispersion time may be 1 hour to 4 hours.

[0183] Optionally, the pore-forming agent may be hydrogen peroxide, and the mass fraction of hydrogen peroxide may be 20%-40%.

[0184] Hydrogen peroxide can react with graphene oxide, etching the graphene oxide sheets, thereby causing holes to appear on the graphene oxide microsheets, thereby obtaining porous graphene oxide microsheets.

[0185] Optionally, the volume ratio of the pore former to the graphene oxide dispersion is 1:(5-50), more preferably 1:(5-20), 1:(8-20).

[0186] Optionally, the obtained graphene oxide dispersion is mixed with a pore-forming agent, and the stirring reaction can be performed by magnetic stirring. Optionally, mechanical stirring can be performed before starting the magnetic stirring. The mechanical stirring time can be 5 minutes to 15 minutes.

[0187] Optionally, the obtained graphene oxide dispersion is mixed with a pore-forming agent, and the stirring reaction can be carried out at a rotation speed of 700 rpm to 1000 rpm.

[0188] Optionally, the obtained graphene oxide dispersion is mixed with a pore-forming agent, and the stirring reaction temperature can be 80°C-120°C.

[0189] Optionally, the obtained graphene oxide dispersion is mixed with a pore-forming agent, and the stirring reaction time can be 1 hour to 4 hours.

[0190] The porosity of the porous graphene oxide microsheets can be adjusted by adjusting the stirring reaction time.

[0191] Optionally, the obtained graphene oxide dispersion is mixed with a pore-forming agent, stirred and reacted for a period of time, and then subjected to solid-liquid separation to obtain a primary precipitate; the primary precipitate is then evenly dispersed with water, and then subjected to solid-liquid separation to obtain a secondary precipitate, and the above operation is repeated 1 to 3 times to obtain a final precipitate for drying and grinding.

[0192] The solid-liquid separation method is centrifugal separation.

[0193] Multiple washings can obtain porous graphene oxide microsheets with high porosity, which is beneficial to improving the ion conductivity of the diaphragm.

[0194] In other embodiments, the preparation method of porous graphene oxide microsheets includes the following steps: providing graphene oxide, wherein the graphene oxide is in the form of flakes; uniformly dispersing the graphene oxide with water to obtain a graphene oxide dispersion; adding thiourea to the obtained graphene oxide dispersion and heating it in a reactor, and finally performing vacuum freeze-drying to obtain porous graphene oxide microsheet powder.

[0195] During the heating process, thiourea decomposes to produce a large amount of ammonia and hydrogen sulfide gas. Since these gases cannot be discharged in the closed environment of the reactor, they will further crush the flaky graphene oxide into tiny porous graphene oxide microsheets.

[0196] Optionally, the mass fraction of the graphene oxide dispersion may be 0.1%-10%.

[0197] Optionally, the graphene oxide and water may be uniformly dispersed by ultrasonic dispersion, and the ultrasonic dispersion time may be 1 h to 3 h.

[0198] Optionally, the mass ratio of thiourea to graphene oxide dispersion can be 1:(50-550).

[0199] Optionally, thiourea is added to the obtained graphene oxide dispersion and heated in a reactor at a temperature of 150° C. to 200° C.

[0200] Optionally, thiourea may be added to the obtained graphene oxide dispersion and heated in the reactor for 4-5 hours.

[0201] The porosity of the porous graphene oxide microsheets can be adjusted by adjusting the heating temperature and / or time.

[0202] Optionally, the temperature of the vacuum freeze-drying process may be -50°C to -80°C.

[0203] Optionally, the vacuum freeze-drying process may be performed for 1 hour to 2 hours.

[0204] Optionally, the vacuum degree of the vacuum freeze-drying process can be 85KPa-95KPa.

[0205] In some embodiments, the preparation method of porous graphene oxide microsheets also includes a doping step: the porous graphene oxide microsheets are evenly dispersed with water to obtain a porous graphene oxide microsheet dispersion, a dopant is added under stirring conditions, and then a hydrothermal reaction is carried out, followed by solid-liquid separation to obtain a precipitate; the obtained precipitate is washed and dried to obtain a doped porous graphene oxide microsheet powder.

[0206] Alternatively, drying may be vacuum freeze drying.

[0207] Optionally, the dopant contains at least one of fluorine, nitrogen, phosphorus, and sulfur. More optionally, the dopant may include one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and thiourea.

[0208] Optionally, the temperature of the hydrothermal reaction may be 60° C.-120° C., and the time may be 1 h-4 h.

[0209] Some parameters such as raw materials and their contents used in the preparation method of the diaphragm provided in the embodiments of the present application can refer to the diaphragm provided in the embodiments of the present application, and will not be repeated here.

[0210] Unless otherwise specified, all raw materials used in the preparation method of the separator can be obtained commercially.

[0211] [Positive electrode]

[0212] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0213] In some embodiments, the positive electrode active material includes a material capable of extracting and inserting lithium.

[0214] As an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, metal chalcogenides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium titanium oxide, and their respective modified compounds. Lithium transition metal oxides may include, but are not limited to, layered structures and spinel structures. Examples of lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0215] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material may include a general formula of Li a Ni b Co c M d O e D f One or more lithium transition metal oxides and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M may include but is not limited to one or more of Ge, Mo, Sn, Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and D may include but is not limited to one or more of N, F, S and Cl.

[0216] In some embodiments, the positive electrode active material may include both a lithium transition metal oxide and a lithium-containing phosphate, thereby facilitating the production of a battery with both high capacity and high reliability.

[0217] As an example, the positive electrode active material may include but is not limited to LiCoO2, LiNiO2, LiMnO2, LiNi 1 / 2 Mn 1 / 2O2、LiMn2O4、Li 4 / 3 Ti 5 / 3 O4、LiNi 1 / 2 Mn 1 / 2 O2、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 O2, LiFePO4, LiMnPO4, Li 1.13 Ti 0.57 Fe 0.3 One or more of S2.

[0218] In some embodiments, the positive electrode active material includes a material capable of extracting and inserting sodium. For example, the positive electrode active material may include, but is not limited to, one or more of layered transition metal oxides (including but not limited to P2 type, O3 type, etc.), polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian materials.

[0219] In some embodiments, as examples, the positive electrode active material may include but is not limited to NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, Na 0.67 MO2 (M includes at least two of Fe, Co, Cr, Mn, Ni, V, Ti, Mo), NaMO2 (M includes at least two of Fe, Co, Ni, V, Ti, Mo), NaFePO4, NaMnPO4, NaCoPO4, Na4Fe3(PO4)2O7, Na3V2(PO4)2F3, Na3V2(PO4)3, Prussian blue, Prussian white, and one or more of their respective modified compounds.

[0220] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0221] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0222] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, fluorinated acrylic resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and one or more of carboxymethyl chitosan (CMCS).

[0223] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0224] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, positive electrode conductive agent, positive electrode binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0225] [Negative electrode]

[0226] The structure and composition of the negative electrode plate can be adjusted according to the type of battery cell.

[0227] In some embodiments, the negative electrode plate may include a negative electrode current collector and a metal layer disposed on at least one surface of the negative electrode current collector. The metal material in the metal layer may include but is not limited to one or more of lithium, lithium alloy, sodium, and sodium alloy.

[0228] A lithium alloy may be an alloy of metallic lithium and other metallic elements or non-metallic elements. For example, the other metallic elements in the lithium alloy may include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, and the non-metallic elements in the lithium alloy may include one or more of boron, carbon, and silicon.

[0229] The sodium alloy may be an alloy of metallic sodium and other metallic elements or non-metallic elements. For example, the other metallic elements in the sodium alloy may include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, and the non-metallic elements in the sodium alloy may include one or more of boron, carbon, and silicon.

[0230] In some embodiments, the negative electrode sheet may include a negative electrode current collector but not a metal layer, so as to be assembled into a negative electrode metal-free battery cell.

[0231] In some embodiments, to improve battery performance, the negative electrode side of a negative-electrode metal-free battery cell may also be provided with some conventional substances that can be used as negative-electrode active materials, such as carbon materials. Although these substances have a certain capacity, their content is relatively small and they are not used as the primary negative-electrode active material in the battery cell. Therefore, the battery cell thus constructed can still be considered a negative-electrode metal-free battery cell.

[0232] In some embodiments, the negative electrode current collector may include a metal foil, a three-dimensional porous current collector, or a composite current collector. As examples of metal foils, copper foil, copper alloy foil, nickel foil, nickel alloy foil, aluminum foil, and aluminum alloy foil may be used. As examples of three-dimensional porous current collectors, copper mesh, nickel mesh, aluminum mesh, foam copper, foam nickel, and foam aluminum may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0233] [Electrolytes]

[0234] In some embodiments, the electrolyte is an electrolyte solution including an electrolyte salt and an organic solvent.

[0235] In some embodiments, the electrolyte includes anions, which may include bis(fluorosulfonyl)imide anions (FSI-), bis(trifluoromethanesulfonyl)imide anions (TFSI-), and - ), dioxalatoborate anion (BOB - ), difluorooxalatoborate anion (DFOB-), difluorobis(oxalatophosphate) anion (DFOP- - ), tetrafluorooxalophosphate anion (TFOP-), difluorophosphate anion (PO2F2 - ), hexafluorophosphate anion (PF6 - ), tetrafluoroborate anion (BF4- ), hexafluoroarsenate anion (AsF6 - ), trifluoromethanesulfonate anion (CF3SO3 - )

[0236] In some embodiments, the electrolyte includes cations, which may include one or more of lithium ions and sodium ions.

[0237] In some embodiments, the concentration of the electrolyte salt may be greater than 0.3 mol / L, and may be greater than 0.7 mol / L. The concentration of the electrolyte salt may further be less than 4 mol / L, and may be less than 2.5 mol / L or less than 1.7 mol / L. When the concentration of the electrolyte salt is within the above range, the electrolyte solution can have suitable ionic conductivity.

[0238] Organic solvent can include but not limited to one or more in esters, ethers, sulfones, nitrile etc.Ester can include but not limited to one or more in carbonate, phosphate, carboxylate, sulfate, sulfonate etc.Carbonate can comprise cyclic carbonate and / or chain carbonate, alternatively, carbonate can comprise cyclic carbonate and chain carbonate simultaneously.Chain carbonate can comprise low-viscosity polar chain carbonate, aliphatic branched-chain carbonate etc.

[0239] As an example, the organic solvent may include, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), tetraethylene glycol dimethyl ether (TEGDME), ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), trimethyl phosphate, 3-methoxypropionitrile, H(CF2)2OCH3, C4F9O CH3, H(CF2)2OCH2CH3, H(CF2)2OCH2CF3, H(CF2)2CH2O(CF2)2H, CF3CHFCF2OCH3, CF3CHFCF2OCH2CH3, 2-trifluoromethylhexafluoropropyl methyl ether, 2-trifluoromethylhexafluoropropyl ethyl ether, 2-trifluoromethylhexafluoropropyl propyl ether, 3-trifluoromethyloctafluorobutyl methyl ether, 3-trifluoromethyloctafluorobutyl ethyl ether, 3-trifluoromethyloctafluorobutyl propyl ether, 4-trifluoromethyl One or more of trifluoromethyl decafluoropentyl methyl ether, 4-trifluoromethyl decafluoropentyl ethyl ether, 4-trifluoromethyl decafluoropentyl propyl ether, 5-trifluoromethyl dodecafluorohexyl methyl ether, 5-trifluoromethyl dodecafluorohexyl ethyl ether, 5-trifluoromethyl dodecafluorohexyl propyl ether, 6-trifluoromethyl tetradecafluoroheptyl methyl ether, 6-trifluoromethyl tetradecafluoroheptyl ethyl ether, 6-trifluoromethyl tetradecafluoroheptyl propyl ether, 7-trifluoromethyl hexafluorooctyl methyl ether, 7-trifluoromethyl hexafluorooctyl ethyl ether, and 7-trifluoromethyl hexafluorooctyl propyl ether.

[0240] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0241] The preparation method of battery cells is well known. In some embodiments, the positive electrode sheet, separator, negative electrode sheet and electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator and negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with the above-mentioned electrolyte, and then vacuum packaged, allowed to stand, formed and other processes to obtain a battery cell. Multiple battery cells can also be further connected in series, in parallel or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0242] The present application also provides an electrical device, which includes a battery provided in the present application. The battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0243] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

[0244] Figure 6 The diagram is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0245] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0246] Example

[0247] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0248] Example 1

[0249] Preparation of porous graphene oxide microsheets

[0250] 2.5g of graphene oxide powder was evenly dispersed in 250mL of pure water to obtain a graphene oxide aqueous solution, which was then ultrasonically dispersed for 2 hours to obtain a uniformly dispersed graphene oxide dispersion. The graphene oxide was in the form of flakes with a lateral dimension of 1μm and a layer thickness of 1nm.

[0251] The graphene oxide dispersion was mixed with 25 mL of a 30% hydrogen peroxide solution, mechanically stirred for 10 minutes, and then magnetically stirred at 100°C for 2 hours at a stirring speed of 800 rpm. After stirring, the resulting mixture was centrifuged to obtain a precipitate. The precipitate was dissolved in pure water and centrifuged again. This process was repeated three times to obtain a pure precipitate. The mixture was then vacuum-dried at 60°C for 6 hours, and the dried product was ground to obtain porous graphene oxide microplatelet powder.

[0252] The lateral size of the porous graphene oxide microsheet is 1 μm, the average pore diameter is 5 nm, the porosity is 25%, the area of ​​pores with a diameter greater than 2 nm accounts for 87% of the total pore area, and the sheet thickness is 1 nm.

[0253] Scanning electron microscopy can be used to distinguish the lateral dimensions of porous graphene oxide microsheets.

[0254] The average pore size, pore size distribution, and porosity of porous graphene oxide microplatelets can be determined by nitrogen adsorption surface area analysis and calculation using the BET (Brunauer Emmett Teller) method, as described in GB / T 19587-2017. The test instrument used was a Micromeritics Tri-Star 3020 surface area and pore size analyzer.

[0255] Preparation of diaphragm

[0256] 2.5 g of the prepared porous graphene oxide microplatelet powder was added to 250 mL of pure water to obtain an aqueous solution of porous graphene oxide microplatelets. 0.1 g of polyvinyl alcohol powder and 0.025 g of polyvinyl pyrrolidone (PVP) powder were added to the aqueous solution of porous graphene oxide microplatelets and magnetically stirred at 800 rpm for 2 h to obtain a slurry.

[0257] The slurry was evenly coated onto a 7μm polyethylene film to a thickness of 3μm. Another 7μm polyethylene film was placed over the slurry-coated side of the separator. The separator was then hot-pressed and vacuum-dried to obtain the desired result. The hot-pressing temperature was 120°C, the pressure was 5 MPa, and the drying time was 5 minutes. The vacuum drying time was 100°C and the drying time was 12 hours.

[0258] The total thickness of the separator is 17 μm, and the thickness of the graphene oxide layer is 3 μm.

[0259] Comparative Example 1

[0260] 2.5g of graphene oxide powder was evenly dispersed in 250mL of pure water to obtain a graphene oxide aqueous solution. 0.1g of polyvinyl alcohol powder and 0.025g of polyvinyl pyrrolidone (PVP) powder were added to the graphene oxide aqueous solution and magnetically stirred at 800rpm for 2h to obtain a slurry. The slurry was evenly coated on a 7μm polyethylene film with a coating thickness of 3μm. Another 7μm polyethylene film was taken to cover the side of the diaphragm coated with the slurry, and the diaphragm was obtained by hot pressing and vacuum drying. The hot pressing temperature was 120℃, the pressure was 5MPa, and the time was 5 minutes. The vacuum drying temperature was 100℃ and the time was 12h. The total thickness of the diaphragm was 17μm, and the thickness of the graphene oxide layer was 3μm.

[0261] Examples 2 to 3 and Comparative Examples 2 to 3

[0262] The preparation method of the diaphragm is similar to that of Example 1, except that porous graphene oxide microsheets with different porosities and average pore sizes are obtained by adjusting the preparation process parameters of the porous graphene oxide microsheets. The specific parameters are shown in Table 1.

[0263] Examples 4 to 6 and Comparative Examples 4 to 5

[0264] The preparation method of the diaphragm is similar to that of Example 1, except that the lateral dimensions of the flake graphene oxide are different, and the lateral dimensions and porosities of the prepared porous graphene oxide microsheets are different. Specific parameters are detailed in Table 1.

[0265] Performance test of diaphragm

[0266] (1) Ionic conductivity test of diaphragm

[0267] The ionic conductivity of the separator was tested according to GB / T 36363-2018. Based on the resistance law, the confined symmetric cell EIS method was used to measure Rs for different separator layers (n) as the separator resistance. The slope k was obtained by plotting Rs vs. n. The ionic conductivity of the separator was calculated given the effective area S and separator thickness. The electrolyte salt was LiFSI at a concentration of 1 mol / L, and the solvent was ethylene glycol dimethyl ether (DME).

[0268] (2) Diaphragm air permeability test

[0269] The membrane air permeability is tested according to GB / T 36363-2018. The time (in seconds) required for 100 mL of air to pass through the membrane is used as the membrane air permeability. The greater the membrane air permeability, the worse the membrane's air permeability. Six or more membrane samples can be tested, and the test results are averaged. The test instrument can be a Kumagai KRK Wangyan air permeability tester.

[0270] (3) Tensile strength test of diaphragm

[0271] The tensile strength of the diaphragm in the transverse direction (TD) and longitudinal direction (MD) was tested according to GB / T 36363-2018.

[0272] Cut the membrane into samples with a width of 10 mm and a length of 150 mm (with the length direction parallel to the transverse direction of the membrane) for testing to determine the tensile strength in the transverse direction (TD). The testing instrument can be a universal tensile testing machine with a tensile rate of 50 mm / min. Six or more membrane samples can be tested, and the test results are averaged.

[0273] Cut the membrane into samples with a width of 10 mm and a length of 150 mm (with the longitudinal direction parallel to the longitudinal direction) for testing to determine the tensile strength in the longitudinal direction (MD). The testing instrument can be a universal tensile testing machine with a tensile rate of 50 mm / min. Six or more membrane samples can be tested, and the test results are averaged.

[0274] (4) Thermal shrinkage test of diaphragm

[0275] The thermal shrinkage of the diaphragm in the transverse direction (TD) and longitudinal direction (MD) is tested according to GB / T 36363-2018. The diaphragm sample is 50 mm wide and 100 mm long, and the hot box temperature is 105°C and the heat treatment time is 1 hour. After completion, the length and width of the diaphragm are measured, and the values ​​are marked as a and b, respectively. The thermal shrinkage in the longitudinal direction (MD) = [(100-a) / 100] × 100%, and the thermal shrinkage in the transverse direction (TD) = [(50-b) / 50] × 100%. During the test, the number of diaphragm samples can be more than 6, and the test results are averaged.

[0276] Next, the above-mentioned separators were assembled into button batteries, and the following performance tests were performed.

[0277] Coin cells can be prepared as follows. Lithium iron phosphate, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed uniformly in a suitable amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 8:1:1 to form a positive electrode slurry. The positive electrode slurry is coated onto aluminum foil, the positive electrode current collector, and dried to form a positive electrode sheet. In an argon-protected glove box, the positive electrode sheet, the separator, and the lithium sheet are assembled into a CR2430 button cell. The electrolyte salt is LiFSI at a concentration of 1 mol / L, and the solvent is ethylene glycol dimethyl ether (DME).

[0278] At 25°C, charge the button cell at a constant current of 0.1C to 3.65V, then charge it at a constant voltage of 3.65V to 0.05C. After allowing the button cell to rest for 10 minutes, discharge it at a constant current of 0.1C to 2.5V. After cycling the button cell twice using the above method, perform the following performance tests.

[0279] A button cell was charged at constant current rates of 0.5C, 1C, and 2C to 3.65V, followed by constant voltage charge at 3.65V to 0.05C. After standing for 10 minutes, the cell was discharged at a constant current of 0.2C to 2.5V. The cell was cycled 100 times using this method to determine the charge capacity and discharge capacity at the 100th cycle. The coulombic efficiency of the cell after 100 cycles is calculated as: discharge capacity at the 100th cycle / charge capacity at the 100th cycle.

[0280] The button cell was charged at a constant current rate of 1C to 3.65V, then charged at a constant voltage rate of 3.65V to 0.05C. After the button cell rested for 10 minutes, it was discharged at a constant current of 0.2C to 2.5V to obtain the discharge capacity of the first cycle. The button cell was cycled 100 times using the above method to obtain the discharge capacity at the 100th cycle. The capacity retention rate of the button cell after 100 cycles = discharge capacity at the 100th cycle / discharge capacity at the first cycle.

[0281] During the test, the number of button battery samples can be more than 6, and the test results are averaged.

[0282] Table 1

[0283]

[0284] Figure 7 The scanning electron microscope (SEM) image of the porous graphene oxide microsheet prepared in Example 1 is shown in FIG. Figure 7 It can be seen that the graphene oxide microsheets of the present application have a porous structure.

[0285] Table 2

[0286]

[0287] It can be seen from the above test results that by arranging porous graphene oxide microsheets between the first porous substrate layer and the second porous substrate layer, and making the lateral size of the porous graphene oxide microsheets 0.5μm-3μm, and the porosity of the porous graphene oxide microsheets 10%-30%, the diaphragm can have high mechanical strength, high thermal stability, high air permeability and high ion conductivity, and can also have the function of dissolving dendrites and reducing the risk of dendrites piercing the diaphragm and contacting the positive electrode to cause internal short circuit of the battery, thereby making the battery have good cycle performance and rate performance.

[0288] If the porosity of porous graphene oxide microsheets is too small, the ion conductivity of the diaphragm will be poor, and the battery performance will be poor. If the porosity of porous graphene oxide microsheets is too high, their own mechanical strength will deteriorate and the risk of pulverization will increase, which can easily cause diaphragm pore blockage, affecting the performance of the battery after multiple charge and discharge cycles. Porous graphene oxide microsheets that are too small can easily fall into the pores of the porous substrate layer, causing diaphragm pore blockage and affecting battery performance. Porous graphene oxide microsheets that are too large are more likely to cause microsheets to stack on each other and cause pore blockage after swelling in the electrolyte, thereby reducing the ion conductivity of the diaphragm and affecting battery performance.

[0289] Example 7

[0290] The preparation method of the diaphragm is similar to that of Example 1, except that the amount of the binder polyvinyl alcohol powder in the graphene oxide layer is different.

[0291] 2.5g of the prepared porous graphene oxide microplatelet powder was added to 250mL of pure water to obtain an aqueous solution of porous graphene oxide microplatelets. 0.04g of polyvinyl alcohol powder and 0.025g of polyvinyl pyrrolidone (PVP) powder were added to the aqueous solution of porous graphene oxide microplatelets and magnetically stirred at 800rpm for 2h to obtain a slurry. The mass fraction of the porous graphene oxide microplatelets in the graphene oxide layer was 97.5%.

[0292] Example 8

[0293] The preparation method of the diaphragm is similar to that of Example 1, except that the amount of the binder polyvinyl alcohol powder in the graphene oxide layer is different.

[0294] 2.5g of the prepared porous graphene oxide microplatelet powder was added to 250mL of pure water to obtain an aqueous solution of porous graphene oxide microplatelets. 0.5g of polyvinyl alcohol powder and 0.025g of polyvinyl pyrrolidone (PVP) powder were added to the aqueous solution of porous graphene oxide microplatelets and magnetically stirred at 800rpm for 2h to obtain a slurry. The mass fraction of the porous graphene oxide microplatelets in the graphene oxide layer was 82.6%.

[0295] Example 9

[0296] The preparation method of the diaphragm is similar to that of Example 1, except that the amount of the binder polyvinyl alcohol powder in the graphene oxide layer is different.

[0297] 2.5g of the prepared porous graphene oxide microplatelet powder was added to 250mL of pure water to obtain an aqueous solution of porous graphene oxide microplatelets. 0.025g of polyvinyl alcohol powder and 0.025g of polyvinyl pyrrolidone (PVP) powder were added to the aqueous solution of porous graphene oxide microplatelets and magnetically stirred at 800rpm for 2h to obtain a slurry. The mass fraction of the porous graphene oxide microplatelets in the graphene oxide layer was 98.0%.

[0298] Example 10

[0299] The preparation method of the diaphragm is similar to that of Example 1, except that the amount of the binder polyvinyl alcohol powder in the graphene oxide layer is different.

[0300] 2.5g of the prepared porous graphene oxide microplatelet powder was added to 250mL of pure water to obtain an aqueous solution of porous graphene oxide microplatelets. 1.25g of polyvinyl alcohol powder and 0.025g of polyvinyl pyrrolidone (PVP) powder were added to the aqueous solution of porous graphene oxide microplatelets and magnetically stirred at 800rpm for 2h to obtain a slurry. The mass fraction of the porous graphene oxide microplatelets in the graphene oxide layer was 66.2%.

[0301] Table 3

[0302]

[0303] From the above test results, it can be seen that the appropriate content of porous graphene oxide microsheets and the appropriate binder content can not only reduce the powder loss phenomenon, but also make the separator have better ion conductivity, and make the battery have better cycle performance and rate performance.

[0304] Examples 11 to 14

[0305] The preparation method of the diaphragm is similar to that of Example 1, except that the thickness of the graphene oxide layer is different. The specific parameters are detailed in Table 4. The thickness of the graphene oxide layer can be adjusted by adjusting the coating weight of the slurry.

[0306] Table 4

[0307]

[0308] From the above test results, it can be seen that a suitable coating thickness can not only better eliminate the dendrites growing on the negative electrode, but also reduce the consumption of lithium ions, thereby enabling the battery to have better cycle performance and higher coulombic efficiency.

[0309] Example 15

[0310] Preparation of porous graphene oxide microsheets

[0311] Same as Example 1.

[0312] Preparation of diaphragm

[0313] 2g of the prepared porous graphene oxide microplatelet powder was added to 250mL of pure water to obtain an aqueous solution of porous graphene oxide microplatelets. 0.1g of polyvinyl alcohol powder, 0.025g of polyvinyl pyrrolidone (PVP) powder, and 0.5g of inorganic nanoparticles SiO2 were added to the aqueous solution of porous graphene oxide microplatelets and magnetically stirred at 800rpm for 2h to obtain a slurry. The volume-distributed particle size Dv50 of the inorganic nanoparticles SiO2 was 160nm.

[0314] The slurry was evenly coated onto a 7μm polyethylene film to a thickness of 3μm. Another 7μm polyethylene film was placed over the slurry-coated side of the separator. The separator was then hot-pressed and vacuum-dried to obtain the desired result. The hot-pressing temperature was 120°C, the pressure was 5 MPa, and the drying time was 5 minutes. The vacuum drying time was 100°C and the drying time was 12 hours.

[0315] The total thickness of the separator is 17 μm, and the thickness of the graphene oxide layer is 3 μm. The mass of the graphene oxide layer is 76.2% by weight of porous graphene oxide microsheets, and the mass of inorganic nanoparticles accounts for 19%.

[0316] Example 16

[0317] Preparation of porous graphene oxide microsheets

[0318] Same as Example 1.

[0319] Preparation of diaphragm

[0320] 1.5g of the prepared porous graphene oxide microplatelet powder was added to 250mL of pure water to obtain an aqueous solution of porous graphene oxide microplatelets. 0.1g of polyvinyl alcohol powder, 0.025g of polyvinyl pyrrolidone (PVP) powder, and 1g of inorganic nanoparticles SiO2 were added to the aqueous solution of porous graphene oxide microplatelets and magnetically stirred at 800rpm for 2h to obtain a slurry. The volume-distributed particle size Dv50 of the inorganic nanoparticles SiO2 was 160nm.

[0321] The slurry was evenly coated onto a 7μm polyethylene film to a thickness of 3μm. Another 7μm polyethylene film was placed over the slurry-coated side of the separator. The separator was then hot-pressed and vacuum-dried to obtain the desired result. The hot-pressing temperature was 120°C, the pressure was 5 MPa, and the drying time was 5 minutes. The vacuum drying time was 100°C and the drying time was 12 hours.

[0322] The total thickness of the separator is 17 μm, and the thickness of the graphene oxide layer is 3 μm. The mass of the graphene oxide layer is 57.1% by weight of porous graphene oxide microsheets and 38.1% by weight of inorganic nanoparticles.

[0323] Table 5

[0324]

[0325] From the above test results, it can be seen that the graphene oxide layer contains an appropriate amount of inorganic nanoparticles, which can further improve the ion conductivity of the separator and further enhance the cycle performance, rate performance and coulombic efficiency of the battery.

[0326] Example 17

[0327] Preparation of porous graphene oxide microsheets

[0328] 2.5g of graphene oxide powder was evenly dispersed in 250mL of pure water to obtain a graphene oxide aqueous solution, which was then ultrasonically dispersed for 2 hours to obtain a uniformly dispersed graphene oxide dispersion. The graphene oxide was in the form of flakes with a lateral dimension of 1μm and a layer thickness of 1nm.

[0329] 0.5g of thiourea was added to a graphene oxide dispersion and heated in a reactor at 180°C for 4.5 hours. After the reaction was complete, the solution was freeze-dried to remove the solvent, yielding porous graphene oxide microplatelet powder. The freeze-drying process was performed at -60°C for 2 hours at a vacuum pressure of 85 kPa.

[0330] The lateral size of the porous graphene oxide microsheets is 1 μm, the average pore size is 6 nm, the porosity is 20%, and the sheet thickness is 1 nm.

[0331] Preparation of diaphragm

[0332] 2.5 g of the prepared porous graphene oxide microplatelet powder was added to 250 mL of pure water to obtain an aqueous solution of porous graphene oxide microplatelets. 0.1 g of polyvinyl alcohol powder and 0.025 g of polyvinyl pyrrolidone (PVP) powder were added to the aqueous solution of porous graphene oxide microplatelets and magnetically stirred at 800 rpm for 2 h to obtain a slurry.

[0333] The slurry was evenly coated onto a 7μm polyethylene film to a thickness of 3μm. Another 7μm polyethylene film was placed over the slurry-coated side of the separator. The separator was then hot-pressed and vacuum-dried to obtain the desired result. The hot-pressing temperature was 120°C, the pressure was 5 MPa, and the drying time was 5 minutes. The vacuum drying time was 100°C and the drying time was 12 hours.

[0334] The total thickness of the separator is 17 μm, and the thickness of the graphene oxide layer is 3 μm.

[0335] Table 6

[0336]

[0337] From the above test results, it can be seen that different preparation processes of porous graphene oxide microsheets can make the separator have high mechanical strength, high thermal stability, high permeability and high ion conductivity, and can also make the battery have good cycle performance and rate performance.

[0338] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A diaphragm, characterized in that: The diaphragm includes a graphene oxide layer and a first porous substrate layer and a second porous substrate layer located on both sides of the graphene oxide layer. The graphene oxide layer includes porous graphene oxide microsheets. The lateral size of the porous graphene oxide microsheets is 0.5 μm-3 μm, and the porosity of the porous graphene oxide microsheets is 10%-30%.

2. The diaphragm according to claim 1, characterized in that The lateral size of the porous graphene oxide microsheet is 0.5 μm-1.5 μm; and / or the porosity of the porous graphene oxide microsheet is 16%-25%.

3. The diaphragm according to any one of claims 1 to 2, characterized in that: The average pore size of the porous graphene oxide microsheets is 1.5 nm to 10 nm; and / or, The area of ​​pores with a pore diameter greater than 2 nm in the porous graphene oxide microsheets accounts for more than 60% of the total pore area; and / or, The specific surface area of ​​the porous graphene oxide microsheet is 50m 2 / g-500m 2 / g.

4. The diaphragm according to claim 3, characterized in that The average pore size of the porous graphene oxide microsheets is 2nm-8nm; and / or, The area of ​​pores with a pore diameter greater than 2 nm in the porous graphene oxide microsheets accounts for 80% to 92% of the total pore area.

5. The diaphragm according to any one of claims 1 to 4, characterized in that: The mass proportion of oxygen element in the porous graphene oxide microsheets is 15%-35%.

6. The diaphragm according to any one of claims 1 to 5, characterized in that: The porous graphene oxide microsheet includes doping elements, and the doping elements include one or more of fluorine, nitrogen, sulfur, and phosphorus; and / or the mass proportion of the doping elements in the porous graphene oxide microsheet is 1%-15%.

7. The diaphragm according to any one of claims 1 to 6, characterized in that: The thickness of the porous graphene oxide microsheet is 1 nm to 2 nm.

8. The diaphragm according to any one of claims 1 to 7, characterized in that: The mass proportion of the porous graphene oxide microsheets in the graphene oxide layer is greater than or equal to 50%.

9. The diaphragm according to claim 8, characterized in that The mass proportion of the porous graphene oxide microsheets in the graphene oxide layer is greater than or equal to 70%.

10. The diaphragm according to any one of claims 1 to 9, characterized in that: The graphene oxide layer further includes inorganic nanoparticles, and the volume distribution particle size Dv50 of the inorganic nanoparticles is 30nm-500nm.

11. The diaphragm according to claim 10, characterized in that The mass proportion of inorganic nanoparticles in the graphene oxide layer is less than or equal to 40%; and / or, The inorganic nanoparticles include one or more of ceramic and solid electrolyte particles.

12. The diaphragm according to any one of claims 1 to 11, characterized in that: The graphene oxide layer has a thickness of 0.5 μm-5 μm.

13. The diaphragm according to any one of claims 1 to 12, characterized in that: The diaphragm satisfies at least one of the following conditions (1) to (9), (1) The graphene oxide layer further includes a binder and a wetting agent; (2) the thickness of the first porous substrate layer is 3 μm-14 μm; (3) the porosity of the first porous substrate layer is 40% to 80%; (4) the first porous substrate layer comprises one or more of polyolefin, polyamide, polyester, and their respective derivatives; (5) The thickness of the second porous substrate layer is 3 μm-14 μm; (6) the porosity of the second porous substrate layer is 40% to 80%; (7) the second porous substrate layer comprises two or more of polyolefin, polyamide, polyester, and their respective derivatives; (8) The total thickness of the diaphragm is 7 μm to 30 μm; (9) The porosity of the diaphragm is 30%-80%.

14. A method for preparing a diaphragm, for preparing the diaphragm according to any one of claims 1 to 13, characterized in that: The steps include: Providing a first porous substrate layer, a second porous substrate layer, and a slurry containing porous graphene oxide microplatelets, wherein the porous graphene oxide microplatelets have a lateral dimension of 0.5 μm to 3 μm and a porosity of 10% to 30%; The slurry is coated on one surface of the first porous substrate layer and / or one surface of the second porous substrate layer, and then the first porous substrate layer and the second porous substrate layer are stacked and compounded together to form a diaphragm, which includes a graphene oxide layer and a first porous substrate layer and a second porous substrate layer located on both sides of the graphene oxide layer.

15. The preparation method according to claim 14, characterized in that The method for preparing the porous graphene oxide microsheet comprises the following steps: Providing graphene oxide, wherein the graphene oxide is in a flake shape; uniformly dispersing the graphene oxide with water to obtain a graphene oxide dispersion; The obtained graphene oxide dispersion is mixed with a pore-forming agent, stirred for a period of time, and then subjected to solid-liquid separation to obtain a precipitate; The obtained precipitate is dried and ground to obtain porous graphene oxide microplatelet powder.

16. The preparation method according to claim 15, characterized in that The method for preparing the porous graphene oxide microsheets satisfies at least one of the following conditions (1) to (5): (1) The mass fraction of the graphene oxide dispersion is 0.1%-10%; (2) The pore-forming agent is hydrogen peroxide, and the mass fraction of the hydrogen peroxide is 20%-40%; (3) The volume ratio of the pore-forming agent to the graphene oxide dispersion is 1:(5-50); (4) mixing the obtained graphene oxide dispersion with a pore-forming agent, and stirring the reaction at a temperature of 80° C. to 120° C.; (5) Mix the obtained graphene oxide dispersion with a pore-forming agent, and stir the reaction for 1 h to 4 h.

17. The preparation method according to claim 14, characterized in that The method for preparing the porous graphene oxide microsheet comprises the following steps: Providing graphene oxide, wherein the graphene oxide is in a flake shape; uniformly dispersing the graphene oxide with water to obtain a graphene oxide dispersion; Thiourea is added to the obtained graphene oxide dispersion and heated in a reactor, and finally subjected to vacuum freeze-drying treatment to obtain porous graphene oxide microsheet powder.

18. The preparation method according to claim 17, characterized in that: The method for preparing the porous graphene oxide microsheets satisfies at least one of the following conditions (1) to (7): (1) The mass fraction of the graphene oxide dispersion is 0.1%-10%; (2) the mass ratio of the thiourea to the graphene oxide dispersion is 1:(50-550); (3) adding thiourea to the obtained graphene oxide dispersion and heating the mixture in a reactor at a temperature of 150° C. to 200° C.; (4) adding thiourea to the obtained graphene oxide dispersion and heating it in a reactor for 4 h to 5 h; (5) The temperature of the vacuum freeze-drying process is -50°C to -80°C; (6) The vacuum freeze-drying treatment time is 1h-2h; (7) The vacuum degree of the vacuum freeze-drying process is 85KPa-95KPa.

19. A battery cell, characterized in that: The invention relates to a diaphragm according to any one of claims 1 to 13 or a diaphragm prepared by the preparation method according to any one of claims 14 to 18.

20. A battery, characterized in that: Comprising the battery cell according to claim 19.

21. An electrical device, characterized in that: The battery according to claim 20 is used to provide electrical energy.

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