Separator, secondary battery, and electric apparatus

Abstract

The present application relates to the technical field of batteries, and relates to a separator, a secondary battery, and an electric apparatus. The secondary battery comprises the separator; the separator comprises a base film and a coating provided on the surface of at least one side of the base film; the coating comprises a solid-state electrolyte; and the solid-state electrolyte includes at least one of an oxide solid-state electrolyte, a sulfide solid-state electrolyte, a borohydride solid-state electrolyte, and a polymer solid-state electrolyte. The technical solution of the present application can improve the cycling resistance of the secondary battery to internal short circuit.

Description

Diaphragms, secondary batteries and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 202510205675.8, filed on February 24, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a separator, a secondary battery, and an electrical device. Background Technology

[0004] Secondary batteries are widely used in consumer electronics, electric vehicles, energy storage, and other fields due to their advantages such as repeated charging and discharging and high energy density. However, a common problem in secondary batteries is the growth of metal dendrites. When these dendrites grow to a certain extent, they can puncture the separator between the positive and negative electrodes, resulting in poor cycle life and resistance to internal short circuits. Summary of the Invention

[0005] The main objective of this application is to provide a separator, a secondary battery, and an electrical device, which aim to improve the cycle resistance to internal short circuits of the secondary battery.

[0006] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a separator, the separator including a base film and a coating disposed on at least one surface of the base film, the coating including a solid electrolyte; the solid electrolyte including at least one of an oxide solid electrolyte, a sulfide solid electrolyte, a borohydride solid electrolyte, and a polymer solid electrolyte.

[0007] In the secondary battery provided in this application, the coating of the separator is configured to include a solid electrolyte. This improves the density and modulus of the coating, effectively preventing dendrite growth and penetration, enhancing dendrite resistance, and strengthening the overall structural stability of the separator, thus improving its compressive strength. Furthermore, the solid electrolyte itself provides ion conductivity, ensuring uniform ion insertion and extraction on the electrode surface, preventing excessively high local ion concentrations that could lead to dendrite formation, and further enhancing dendrite resistance. This reduces the risk of internal short circuits during battery cycling and improves the battery's resistance to internal short circuits. The solid electrolyte is selected from at least one of oxide solid electrolytes, sulfide solid electrolytes, borohydride solid electrolytes, and polymer solid electrolytes. These solid electrolytes exhibit high stability, effectively suppressing dendrite growth and penetration, thereby reducing the risk of internal short circuits during battery cycling and improving the battery's resistance to internal short circuits.

[0008] In one embodiment, the content of the solid electrolyte in the coating is 35wt%-97wt%.

[0009] The separator in this application uses a suitable amount of solid electrolyte, which ensures good ion conductivity, enabling efficient lithium-ion transport during charging and discharging, thereby improving the rate performance of the secondary battery. Furthermore, it effectively suppresses dendrite formation, improves dendrite resistance, and enhances the overall structural stability of the separator, increasing its compressive strength and effectively reducing the risk of internal short circuits during battery cycling, thus improving the battery's resistance to internal short circuits. Simultaneously, it also allows the secondary battery to maintain good ion conduction uniformity during cycling, reducing electrode material loss, improving capacity retention, and extending the battery's cycle life.

[0010] In one embodiment, the particle size of the solid electrolyte is 5nm-30nm.

[0011] The separator in this application uses nanoscale solid electrolyte particles, which provides more ion transport channels, thereby improving the ion conductivity of the separator. This facilitates rapid ion exchange during high-rate charge and discharge, improving the charge and discharge efficiency of the secondary battery. Simultaneously, it allows for a denser packing structure, making the separator more compact, enhancing its mechanical strength, effectively preventing dendrite penetration, improving dendrite resistance, and increasing the separator's compressive strength, thus improving the secondary battery's cycle life and resistance to internal short circuits.

[0012] In one embodiment, the thickness of the coating is 0.5 μm to 20 μm.

[0013] This application uses a coating of appropriate thickness, which can effectively ensure that the secondary battery has both good resistance to internal short circuits and good rate performance.

[0014] In one embodiment, the ionic conductivity of the membrane is 0.3 ms / cm to 5 ms / cm.

[0015] The separator of this application has a relatively high ionic conductivity, which helps maintain the balance of ion transport within the secondary battery, avoids excessive local ion concentration leading to dendrite formation, improves dendrite resistance, and thus reduces the risk of internal short circuits during battery cycling, enhancing the battery's resistance to internal short circuits. Simultaneously, it reduces ion transport resistance, lowers the battery's internal resistance, improves charge transport efficiency, and increases the battery's energy density.

[0016] In one embodiment, the coating further includes ceramic particles, wherein the content of the ceramic particles in the coating is 1wt%-73wt%.

[0017] The ceramic particles in this application act as a physical barrier, increasing the difficulty for dendrites to penetrate the separator, thereby improving the separator's dendrite resistance, reducing the risk of internal short circuits during battery cycling, and enhancing the battery's resistance to internal short circuits. The coating in this application contains an appropriate amount of ceramic particles and solid electrolyte, which not only improves the battery's resistance to internal short circuits but also facilitates the processing and fabrication of the separator.

[0018] In one embodiment, the coating further includes an adhesive, wherein the content of the adhesive in the coating is 2wt%-10wt%.

[0019] The coating of the separator in this application includes an appropriate amount of adhesive, which can ensure a good adhesion between the coating and the base membrane, thereby ensuring good overall stability of the separator and improving the cycle resistance to internal short circuits of the secondary battery.

[0020] In one embodiment, two base films are provided, and the coating is provided between the two base films and on the outer side of at least one base film.

[0021] The separator of this application, employing the above-described structure, can further enhance the cycle resistance to internal short circuits in secondary batteries. In one embodiment, the separator further includes an adhesive layer, which is disposed on the outer side of the base film and / or the outer side of the coating.

[0022] This application provides an adhesive layer on the outer side of the base film and / or the outer side of the coating, which can ensure good adhesion between the separator and the electrode plates in the wound cell or stacked cell, thereby ensuring the stability of the overall structure of the wound cell or stacked cell.

[0023] In one embodiment, the secondary battery further includes a positive electrode sheet, the positive electrode sheet comprising a positive active material, the positive active material comprising a sodium-containing active material; the solid electrolyte comprises at least one of sodium alumina, sodium thiophosphate, sodium borohydride, sodium superionic conductor, and polyethylene oxide.

[0024] The secondary battery in this application uses a sodium-ion battery, in which the solid electrolytes such as sodium alumina, sodium thiophosphate, sodium borohydride, sodium superionic conductor, and polyethylene oxide have high stability, can effectively suppress dendrite growth and penetration, effectively reduce the risk of internal short circuit during sodium-ion battery cycling, and improve the cycle resistance to internal short circuit of sodium-ion battery.

[0025] In one embodiment, the secondary battery further includes a negative electrode sheet, which includes a negative current collector and a conductive coating disposed on at least one side surface of the negative current collector.

[0026] The secondary battery described in this application is a negative electrode-free sodium-ion battery. The coating of the separator in this negative electrode-free sodium-ion battery is configured to contain a solid electrolyte. On one hand, this improves the density and modulus of the coating, effectively preventing dendrite growth and penetration, enhancing dendrite resistance, and strengthening the overall structural stability of the separator, thus improving its compressive strength. On the other hand, the solid electrolyte itself provides ion conductivity, ensuring that ions can be uniformly inserted and extracted on the electrode surface, preventing excessively high local ion concentrations that could lead to dendrite formation, and further improving dendrite resistance. This reduces the risk of internal short circuits during cycling of the negative electrode-free sodium-ion battery and improves its resistance to internal short circuits during cycling.

[0027] A second aspect of this application provides a separator, the separator comprising a base membrane and a coating disposed on at least one side of the base membrane, the coating comprising a solid electrolyte;

[0028] The solid electrolyte includes at least one of oxide solid electrolyte, sulfide solid electrolyte, borohydride solid electrolyte, and polymer solid electrolyte.

[0029] In one implementation, any of the following conditions are met:

[0030] The content of the solid electrolyte in the diaphragm is 35wt%-99wt%;

[0031] The particle size of the solid electrolyte is 5nm-30nm;

[0032] The thickness of the coating is 0.5μm-20μm;

[0033] The ionic conductivity of the membrane is 0.3 ms / cm to 5 ms / cm;

[0034] The coating also includes ceramic particles;

[0035] The coating also includes an adhesive.

[0036] In one embodiment, two base films are provided, and the coating is disposed between the two base films and on the outer side of at least one base film; and / or,

[0037] The diaphragm further includes an adhesive layer disposed on the outside of the base film and / or the outside of the coating.

[0038] A third aspect of this application also provides an electrical device, which includes the secondary battery provided in the first aspect of this application.

[0039] In the secondary battery provided in this application, the coating of the separator is configured to include a solid electrolyte. This improves the density and modulus of the coating, effectively preventing dendrite growth and penetration, enhancing dendrite resistance, and strengthening the overall structural stability of the separator, thus improving its compressive strength. Furthermore, the solid electrolyte itself provides ion conductivity, ensuring uniform ion insertion and extraction on the electrode surface, preventing excessively high local ion concentrations that could lead to dendrite formation, and further enhancing dendrite resistance. This reduces the risk of internal short circuits during battery cycling and improves the battery's resistance to internal short circuits. The solid electrolyte is selected from at least one of oxide solid electrolytes, sulfide solid electrolytes, borohydride solid electrolytes, and polymer solid electrolytes. These solid electrolytes possess high stability and can effectively suppress dendrite growth and penetration, thereby reducing the risk of internal short circuits during battery cycling and improving the battery's resistance to internal short circuits. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0041] Figure 1 is a schematic diagram of a secondary battery in some embodiments of this application;

[0042] Figure 2 is an exploded view of the secondary battery in some embodiments of this application;

[0043] Figure 3 is a schematic cross-sectional view of the diaphragm in some embodiments of this application.

[0044] Explanation of reference numerals in the attached figures: 5, secondary battery; 51, casing; 52, electrode assembly; 53, end cap assembly; 521, separator; 521a, base film; 521b, coating; 521c, adhesive layer.

[0045] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0046] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0047] The following detailed description, with appropriate reference to the accompanying drawings, discloses the diaphragm, its preparation method, the secondary battery, and the power supply device of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0048] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0050] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0051] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0052] The problem of metal dendrite growth in secondary batteries is difficult to solve fundamentally. Currently, the common approach is to increase the density of the coating on the separator surface to suppress metal dendrite growth. However, an overly dense separator surface can degrade ion transport capabilities, leading to increased dendrite formation at localized defects (locations with high ion concentrations), resulting in poor dendrite resistance of the separator. When metal dendrites grow to a certain extent, they can puncture the separator between the positive and negative electrodes of the secondary battery, leading to poor cycle life and resistance to internal short circuits.

[0053] To address the aforementioned issues, the first aspect of this application provides a secondary battery designed to improve the cycle resistance to internal short circuits.

[0054] In the secondary battery provided in this application, the coating of the separator is configured to include a solid electrolyte. This improves the density and modulus of the coating, effectively preventing dendrite growth and penetration, enhancing dendrite resistance, and strengthening the overall structural stability of the separator, thus improving its compressive strength. Furthermore, the solid electrolyte itself provides ion conductivity, ensuring uniform ion insertion and extraction on the electrode surface, preventing excessively high local ion concentrations that could lead to dendrite formation, and further enhancing dendrite resistance. This reduces the risk of internal short circuits during battery cycling and improves the battery's resistance to internal short circuits. The solid electrolyte is selected from at least one of oxide solid electrolytes, sulfide solid electrolytes, borohydride solid electrolytes, and polymer solid electrolytes. These solid electrolytes possess high stability and can effectively suppress dendrite growth and penetration, thereby reducing the risk of internal short circuits during battery cycling and improving the battery's resistance to internal short circuits.

[0055] Normally, during the charging and discharging process of a secondary battery, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through.

[0056] [Septum]

[0057] A diaphragm is a membrane material placed between the positive electrode and the negative current collector to prevent short circuits between the positive and negative electrodes and to allow active ions to pass through.

[0058] In this embodiment, the diaphragm includes a base membrane and a coating disposed on at least one surface of the base membrane. This application does not impose any particular limitation on the type of base membrane; any known porous membrane with good chemical and mechanical stability can be selected.

[0059] In some embodiments, the base film may be made of at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0060] In some embodiments, the base film material includes one or more composites of polyethylene, polypropylene, nonwoven fabric, and polyimide. Optionally, the thickness is 5μm-40μm (e.g., 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, and any range between two endpoints).

[0061] In some embodiments, the coating includes a solid electrolyte. This application sets the membrane coating to include a solid electrolyte, which on the one hand can improve the coating's density and modulus strength, effectively preventing dendrite growth and penetration, improving dendrite resistance, and enhancing the overall structural stability of the membrane, thus improving its compressive strength. On the other hand, the solid electrolyte itself can play a role in ion conduction, ensuring that ions can be uniformly inserted and extracted on the electrode surface, avoiding excessively high local ion concentrations that could lead to dendrite formation, thereby improving dendrite resistance. This can reduce the risk of internal short circuits during secondary battery cycling and improve the secondary battery's cycle resistance to internal short circuits.

[0062] In some embodiments, the solid electrolyte includes at least one of oxide solid electrolyte, sulfide solid electrolyte, borohydride solid electrolyte, and polymer solid electrolyte.

[0063] In some embodiments, the secondary battery includes a sodium-ion battery, and the solid electrolyte includes at least one of sodium alumina, sodium thiophosphate, sodium borohydride, sodium superionic conductor, and polyethylene oxide.

[0064] In some embodiments, the secondary battery includes a lithium-ion battery, and the solid electrolyte includes at least one of lithium lanthanum zirconium oxide / lithium thiophosphate, lithium borohydride, and lithium superionic conductor.

[0065] The solid electrolyte selected in this application has high stability, can effectively suppress dendrite growth and penetration, effectively reduce the risk of internal short circuit during secondary battery cycling, and improve the cycling resistance to internal short circuit of secondary battery.

[0066] In some embodiments, the content of solid electrolyte in the coating is 35wt%-97wt% (e.g., 35wt%, 50wt%, 75wt%, 80wt%, 85wt%, 90wt%, 97wt%, and any range between two endpoints).

[0067] The separator in this application uses a suitable amount of solid electrolyte, which ensures good ion conductivity, enabling efficient lithium-ion transport during charging and discharging, thereby improving the rate performance of the secondary battery. Furthermore, it effectively suppresses dendrite formation, improves dendrite resistance, and enhances the overall structural stability of the separator, increasing its compressive strength and effectively reducing the risk of internal short circuits during battery cycling, thus improving the battery's resistance to internal short circuits. Simultaneously, it also allows the secondary battery to maintain good ion conduction uniformity during cycling, reducing electrode material loss, improving capacity retention, and extending the battery's cycle life.

[0068] In some embodiments, the particle size of the solid electrolyte is 5nm-30nm (e.g., 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, and any range between two endpoints).

[0069] The separator in this application uses nanoscale solid electrolyte particles, which provides more ion transport channels, thereby improving the ion conductivity of the separator. This facilitates rapid ion exchange during high-rate charge and discharge, improving the charge and discharge efficiency of the secondary battery. Simultaneously, it allows for a denser packing structure, making the separator more compact, enhancing its mechanical strength, effectively preventing dendrite penetration, improving dendrite resistance, and increasing the separator's compressive strength, thus improving the secondary battery's cycle life and resistance to internal short circuits.

[0070] In some embodiments, the thickness of the coating is 0.5 μm-20 μm (e.g., 0.5 nm, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, and any range between two endpoints).

[0071] This application selects a coating of appropriate thickness to effectively ensure that the secondary battery simultaneously maintains good resistance to internal short circuits and good rate performance. If the coating thickness is less than 0.5 μm, the thinner solid electrolyte coating can reduce the direct contact between the positive and negative electrodes to some extent, reducing the risk of short circuits. However, due to its limited barrier capacity, when stress changes or dendrite growth occur inside the secondary battery, it may not be able to completely prevent the contact between the positive and negative electrodes, resulting in relatively weak resistance to internal short circuits. At the same time, if the coating is too thin, it may not provide enough ion conduction channels, leading to insufficient ion supply at high rates, limiting the battery's charge and discharge efficiency, and causing a decrease in the battery's rate performance. If the coating thickness is greater than 20 μm, the excessive thickness may reduce the flexibility of the separator, making it prone to cracking or detachment during secondary battery assembly or use, which increases the risk of internal short circuits. Moreover, an excessively thick coating may affect ion conduction efficiency, leading to problems such as local overheating, and may also indirectly cause internal short circuits. In addition, if the coating is too thick, the ion conduction path becomes longer, and the ion conduction resistance increases, leading to intensified polarization of the secondary battery, increased internal resistance, and a significant decrease in the rate performance of the secondary battery.

[0072] In some embodiments, the ionic conductivity of the membrane is 0.3 ms / cm to 5 ms / cm (e.g., 0.3 ms / cm, 1 ms / cm, 2 ms / cm, 3 ms / cm, 4 ms / cm, 5 ms / cm, and any range between two endpoints).

[0073] The separator of this application has a relatively high ionic conductivity, which helps maintain the balance of ion transport within the secondary battery, avoids excessive local ion concentration leading to dendrite formation, improves dendrite resistance, and thus reduces the risk of internal short circuits during battery cycling, enhancing the battery's resistance to internal short circuits. Simultaneously, it reduces ion transport resistance, lowers the battery's internal resistance, improves charge transport efficiency, and increases the battery's energy density.

[0074] In some embodiments, the coating further includes ceramic particles. The ceramic particles can act as a physical barrier, increasing the difficulty for dendrites to penetrate the separator, thereby improving the separator's dendrite resistance, reducing the risk of internal short circuits during secondary battery cycling, and enhancing the secondary battery's cycle resistance to internal short circuits.

[0075] In some embodiments, the content of ceramic particles in the coating is 1wt%-73wt% (e.g., 1wt%, 10wt%, 20wt%, 50wt%, 70wt%, 73wt%, and any range between two endpoints). The coating of this application contains an appropriate amount of ceramic particles and solid electrolyte, which can improve the cycle resistance to internal short circuits of the secondary battery and also facilitate the processing and fabrication of the separator. If the coating of this application only contains solid electrolyte, it will have poor flexibility, be difficult to process and fabricate, and may lead to electrolyte agglomeration, blocking ion channels and hindering ion conduction. If the amount of ceramic particles in the coating is too high, it will reduce the effective porosity of the separator, thereby causing a decrease in the rate performance of the secondary battery.

[0076] In some embodiments, the ceramic particles include, but are not limited to, at least one of aluminum oxide (Al2O3), alumina, boehmite (γ-AlOOH), silicon dioxide (SiO2), titanium dioxide (TiO2), and zirconium dioxide (ZrO2).

[0077] In some embodiments, the coating further includes an adhesive, the content of which is 2wt%-10wt% (e.g., 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, and any range between two endpoints).

[0078] The coating of the separator in this application includes an appropriate amount of adhesive, which ensures good adhesion between the coating and the base membrane, thereby ensuring good overall stability of the separator and improving the cycle resistance to internal short circuits of the secondary battery. If the amount of adhesive is too small, the adhesion effect will be poor and the coating structure will have low stability. If the amount of adhesive is too large, it may fill the pores of the separator, resulting in a decrease in the porosity of the separator, an increase in the resistance to active ion migration, and a decrease in the charge and discharge performance of the secondary battery. Furthermore, excessive adhesion may cause decomposition and softening at high temperatures, which will reduce the thermal stability of the separator and increase the risk of thermal runaway of the secondary battery.

[0079] In some embodiments, the adhesive includes, but is not limited to, at least one of polyvinylidene fluoride, styrene-butadiene rubber, polymethyl methacrylate, sodium carboxymethyl cellulose, and polyacrylic acid.

[0080] Please refer to Figure 3, where Figures 3(a) to 3(e) are cross-sectional structural schematic diagrams of some embodiments of the diaphragm 321 of this application.

[0081] Referring to Figure 3(a), in some embodiments, a coating 521b is provided on one side surface of the base film 521a, and the coating 521b is located on the side surface of the base film 521a facing the negative electrode side. Since dendrites are generated only on the negative electrode side and not on the positive electrode side during the charging and discharging process of the secondary battery, the embodiment of this application provides the coating 521b on the side surface of the base film 521a facing the negative electrode side, which can more effectively suppress dendrite growth and penetration.

[0082] Please refer to Figure 3(b). In some embodiments, coatings 521b are provided on both sides of the base film 521a, thereby improving the cycle resistance of the secondary battery.

[0083] In some embodiments, two base films 521a are provided, and a coating 521b is provided between the two base films 521a and on the outer side of at least one base film 521a. The separator 521 of this application, employing the above structure, can further improve the cycle resistance to internal short circuits of the secondary battery.

[0084] Referring to Figure 3(c), in some embodiments, two base films 521a are provided, and a coating 521b is provided between the two base films 521a, on the outer side of the base film 521a near the positive electrode. In this embodiment, the coating 521b near the negative electrode is built in. During charging, the large pores of the base film 521a on the negative electrode side can constrain the regular deposition of metal and prevent disordered dendrite growth. At the same time, the built-in coating 521b can prevent dendrites from piercing the separator.

[0085] Referring to Figure 3(d), in some embodiments, two base films 521a are provided, and a coating 521b is provided between the two base films 521a, on the outer side of the base film 521a near the negative electrode side. In the embodiments of this application, the coating 521b near the positive electrode side is built in, further shortening the distance between the two coatings 521b and enhancing the internal short-circuit resistance of the secondary battery.

[0086] Please refer to Figure 3(e). In some embodiments, two base films 521a are provided, and coatings 521b are provided between the two base films 521a and on the outer side of the two base films 521a. This can further shorten the distance between two adjacent coatings 521b and further improve the cycle resistance to internal short circuits of the secondary battery.

[0087] In some embodiments, the diaphragm 521 further includes an adhesive layer 521c, which is disposed on the outside of the base film 521a and / or the outside of the coating 521b.

[0088] This application provides an adhesive layer 521c on the outer side of the base film 521a and / or the outer side of the coating 521b, which can ensure good adhesion between the separator and the electrode plates in the wound cell or stacked cell, thereby ensuring the stability of the overall structure of the wound cell or stacked cell.

[0089] In some embodiments, the adhesive of the adhesive layer 521c includes, but is not limited to, at least one of polyvinylidene fluoride, styrene-butadiene rubber, polymethyl methacrylate, sodium carboxymethyl cellulose, and polyacrylic acid.

[0090] Optionally, the unit area mass of the adhesive in adhesive layer 521c is 0.5 g / m². 2 -2g / m 2 (e.g., 0.5g / m) 2 1g / m 2 1.5g / m 2 2g / m 2 And the interval value between any two endpoints). The amount of adhesive used in the adhesive layer can be determined according to the cell type, and is not limited here.

[0091] Please refer to Figures 3(a)-(e) again. An adhesive layer 521c is provided on the outer side of the base film 521a and / or the outer side of the coating 521b. This can ensure good adhesion between the separator and the electrode in the wound cell or stacked cell, thereby ensuring the stability of the overall structure of the wound cell or stacked cell.

[0092] It should be noted that cylindrical battery cells have strong self-binding properties, so there is no need to design an adhesive layer.

[0093] [Positive electrode plate]

[0094] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive electrode material.

[0095] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0096] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0097] In some embodiments, the secondary battery is a lithium-ion battery, and the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0098] In some embodiments, the secondary battery is a sodium-ion battery, and the positive electrode active material in the positive electrode slurry can be a positive electrode active material known in the art for sodium-ion batteries.

[0099] As an optional embodiment of this application, in the sodium transition metal oxide, the transition metal can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and the sodium transition metal oxide is, for example, Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0100] As an optional embodiment of this application, the polyanionic compound may be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state.

[0101] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0102] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, tetrahedral unit (ZO) y ) m+ And a class of compounds with optional halide anions, where Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0103] Prussian blue compounds can contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na. a Me b Me' c(CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0104] In some embodiments, the positive electrode active material layer may optionally include an adhesive. As an example, the adhesive may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0105] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0107] [Negative electrode plate]

[0108] The negative electrode of a conventional secondary battery includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0109] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0110] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0111] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0112] In some embodiments, the negative electrode active material layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0113] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0115] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0116] In some embodiments, the secondary battery is a negative electrode-less battery. A negative electrode-less battery eliminates the traditional pre-prepared negative electrode film. Initially, its negative electrode side consists only of a current collector, such as copper foil. During charging, active ions released from the positive electrode (sodium ions in a sodium-ion battery, for example) migrate to the negative electrode under the influence of an electric field and directly deposit metallic sodium (or other corresponding metals) on the surface of the negative electrode current collector. During discharge, the metallic sodium previously deposited on the surface of the negative electrode current collector releases sodium ions again. These sodium ions migrate back to the positive electrode through the electrolyte and react with the positive electrode material, thus enabling the battery to discharge.

[0117] Because negative electrode-less batteries eliminate the volume and weight occupied by the traditional negative electrode film, they can theoretically accommodate more positive electrode material and electrolyte within the same battery volume or weight constraints, potentially significantly increasing the battery's energy density. Furthermore, taking sodium batteries as an example, the sodium metal layer formed during charging acts as the negative electrode, possessing a large theoretical capacity, which can improve the battery's energy density and power.

[0118] However, the nucleation and growth of active ions (such as sodium ions) are significantly limited by the thermodynamics of the negative electrode current collector (heterogeneous substrates such as copper and aluminum): for example, there is a large lattice mismatch between the current collector surface and the metal; the miscibility between the current collector surface and the metal is extremely small; the metal on the current collector surface has low adsorption free energy and high surface diffusion energy, resulting in a high direct nucleation energy barrier; and the randomly distributed structural defects such as grain boundaries and dislocations on the current collector surface preferentially become nucleation sites for metal deposition, leading to a random and uneven distribution of metal nuclei deposited on the current collector surface. This, in turn, causes the growth of porous moss-like morphology, i.e., the metal deposition layer has uneven deposition problems, which will aggravate the side reactions with the electrolyte, resulting in the generation of a large amount of dead lithium / sodium and low coulombic efficiency, thus affecting the cycle life of the battery.

[0119] To address the aforementioned issues, in some embodiments, the negative electrode includes a negative current collector and a conductive coating disposed on at least one surface of the negative current collector. This conductive coating increases the affinity between the metal deposition layer and the surface of the negative current collector, thereby improving the uniformity of the metal deposition layer. The thickness of the conductive coating is not limited herein.

[0120] In some embodiments, the conductive coating includes a conductive agent and an adhesive, and the ratio of the conductive agent and the adhesive is not limited. As an example, the conductive coating is a conductive carbon layer, which includes a conductive carbon material and an adhesive. The conductive carbon material includes, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The adhesive includes, but is not limited to, at least one of sodium carboxymethyl cellulose, sodium polyacrylate, and sodium alginate.

[0121] In some embodiments, the secondary battery of this application is a negative electrode-free sodium-ion battery. The coating of the separator in the negative electrode-free sodium-ion battery is configured to contain a solid electrolyte. On the one hand, this can improve the density and modulus of the coating, effectively prevent the growth and penetration of dendrites, improve dendrite resistance, and enhance the overall structural stability of the separator, thereby improving the separator's compressive strength. On the other hand, the solid electrolyte itself can play a role in ion conduction, ensuring that ions can be uniformly inserted and extracted on the electrode surface, avoiding excessively high local ion concentrations that could lead to dendrite formation, and improving dendrite resistance. This can reduce the risk of internal short circuits during the cycling process of the negative electrode-free sodium-ion battery and improve its cycle resistance to internal short circuits.

[0122] [Electrolytes]

[0123] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0124] In some embodiments, the electrolyte may be an electrolyte solution, which includes an electrolyte salt and a solvent.

[0125] In some embodiments, the secondary battery is a lithium-ion battery, and the electrolyte includes lithium hexafluorophosphate or a mixture of lithium hexafluorophosphate and other lithium salts. The other lithium salts may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. The solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0126] In some embodiments, the secondary battery is a sodium-ion battery, and the electrolyte salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium fluorosulfonylimide, and sodium trifluoromethanesulfonate; the solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,3-dioxolane, 1,2-dimethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0127] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0128] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0129] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0130] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured secondary battery 5 as an example.

[0131] In some embodiments, referring again to FIG2, the outer packaging may include a housing 51 and an end cap assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the end cap assembly 53 is capable of covering the opening and is configured to close the receiving cavity. A positive electrode, a negative electrode, and a separator 521 may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0132] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0133] The second aspect of this application also provides a separator, which is the separator described in the secondary battery provided in the first aspect of this application. Its specific configuration can be referred to the above embodiments, and will not be repeated here.

[0134] In some embodiments, the method for preparing the diaphragm of this application includes the following steps:

[0135] A coating slurry is prepared, wherein the coating slurry includes a solid electrolyte, and the solid electrolyte includes at least one of oxide solid electrolyte, sulfide solid electrolyte, borohydride solid electrolyte, and polymer solid electrolyte;

[0136] The coating slurry is applied to at least one side of the base film and dried to obtain a diaphragm.

[0137] The membrane preparation method provided in this application is relatively simple to operate, and the coating of the prepared membrane contains a solid electrolyte. On the one hand, it can improve the density and modulus of the coating, effectively prevent dendrite growth and penetration, improve dendrite resistance, and enhance the overall structural stability of the membrane and improve the membrane's compressive strength. On the other hand, the solid electrolyte itself can play a role in ion conduction, ensuring that ions can be uniformly inserted and extracted on the electrode surface, avoiding excessively high local ion concentrations that lead to dendrite formation, and improving dendrite resistance. This can reduce the risk of internal short circuits during the cycling of the secondary battery and improve the cycling resistance to internal short circuits of the secondary battery.

[0138] In some embodiments, the step of preparing the coating slurry includes:

[0139] Solid electrolytes are mixed with ceramic particles, and a solvent is added and stirred to obtain a dispersion. A binder is added to the dispersion and stirred to obtain a coating slurry.

[0140] In some embodiments, a dispersing stabilizer is added before the step of adding the binder to the dispersion. The function of the dispersing stabilizer is to make the particles dispersed evenly and to avoid the slurry gelling and being difficult to process. The dispersing stabilizer includes, but is not limited to, sodium carboxymethyl cellulose, acrylate, etc.

[0141] In some embodiments, two base films are provided. The step of applying a coating slurry to at least one side surface of the base film and drying it to obtain a diaphragm includes: combining two rolls of base films coated with a coating layer and an adhesive layer using a roller press under the conditions of a pressure of 0.3MPa-3MPa (e.g., 0.3MPa, 1MPa, 1.5MPa, 2MPa, 2.5MPa, 3MPa and any range between two endpoints) and a temperature of 25℃-60℃ (e.g., 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃ and any range between two endpoints).

[0142] The separator prepared in this embodiment includes two base films and at least two coatings, which can further improve the cycle resistance to internal short circuits of the secondary battery.

[0143] The membrane structure prepared according to the embodiments of this application can be seen in Figures 3(a) to 3(e).

[0144] The parameters such as the material and thickness of the base membrane, the thickness of the coating, the content and particle size of the solid electrolyte, and the ionic conductivity of the diaphragm can be referred to in the above embodiments, and will not be repeated here.

[0145] The fourth aspect of this application also provides an electrical device, which includes the secondary battery provided in the first aspect of this application. The electrical device of this application has at least all the effects of the aforementioned secondary battery, which will not be elaborated further here. The secondary 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 may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0146] As an example, the electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, a mobile phone, a tablet computer, a laptop computer, etc.

[0147] Example

[0148] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0149] Example 1

[0150] [Positive electrode plate]

[0151] The positive electrode active material sodium iron pyrophosphate, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of NMP solvent at a weight ratio of 93:4:3 to form a uniform positive electrode slurry. The positive electrode slurry was then coated onto the surface of the positive electrode current collector aluminum foil, with a coating weight ≤12mg / cm². 2 After drying and cold pressing, a positive electrode sheet is obtained.

[0152] [Negative electrode plate]

[0153] Carbon nanotubes (CNTs) and sodium carboxymethyl cellulose (CMC) were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 50:50 to form an interface modification layer slurry. The interface modification layer slurry was then coated onto the surface of the copper foil of the negative electrode current collector, with a coating thickness of 5 μm. After drying, the negative electrode sheet was obtained.

[0154] [Septum]

[0155] By weight, 85 parts of sodium borohydride (NBH) solid electrolyte powder and 10 parts of Al2O3 ceramic particles were mixed and added to an appropriate amount of N-methylpyrrolidone solvent. The mixture was stirred to obtain a dispersion. Then, 5 parts of PVDF binder were added to the dispersion and stirred to obtain a coating slurry. The coating slurry was coated on both surfaces of a 7 μm thick PE base film. After drying, a coating with a thickness of 4 μm was formed, thus obtaining the separator.

[0156] Electrolyte

[0157] Fully dried NaPF6 was dissolved in diethylene glycol dimethyl ether (DEGDME) to prepare an electrolyte with a concentration of 1 mol / L.

[0158] [Non-anode-free sodium metal battery]

[0159] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The cells are then wound to obtain a bare cell. The bare cell is placed in outer packaging, injected with prepared electrolyte, and undergoes processes such as encapsulation, electrolyte injection, formation, and venting to obtain a sodium metal battery without a negative electrode.

[0160] Example 2

[0161] The difference between Example 2 and Example 1 is that the coating thickness is 2μm, while all other aspects are the same as in Example 1.

[0162] Example 3

[0163] The difference between Example 3 and Example 1 is that the coating thickness is 3 μm, while all other aspects are the same as in Example 1.

[0164] Example 4

[0165] The difference between Example 4 and Example 1 is that the coating thickness is 6 μm, while all other aspects are the same as in Example 1.

[0166] Example 5

[0167] The difference between Example 5 and Example 1 is that the coating thickness is 8 μm, while all other aspects are the same as in Example 1.

[0168] Example 6

[0169] The difference between Example 6 and Example 1 is that the coating thickness is 20 μm, while all other aspects are the same as in Example 1.

[0170] Example 7

[0171] The difference between Example 7 and Example 1 is that the solid electrolyte is sodium thiophosphate (NPS), while everything else is the same as in Example 1.

[0172] Example 8

[0173] The difference between Example 8 and Example 1 is that the solid electrolyte is a sodium superionic conductor (NASICON for short), while everything else is the same as in Example 1.

[0174] Example 9

[0175] The difference between Example 9 and Example 1 is that the solid electrolyte is sodium-alumina (i.e., sodium-Al2O3), while all other aspects are the same as in Example 1.

[0176] Example 10

[0177] The difference between Example 10 and Example 1 is that the solid electrolyte is polyethylene oxide (PEO), while everything else is the same as in Example 1.

[0178] Example 11

[0179] The difference between Example 11 and Example 1 is that the mass of the solid electrolyte powder accounts for 75% of the total mass of the coating, and the mass of the ceramic particles accounts for 20% of the total mass of the coating. All other aspects are the same as in Example 1.

[0180] Example 12

[0181] The difference between Example 13 and Example 1 is that the mass of the solid electrolyte powder accounts for 70% of the total mass of the coating, and the mass of the ceramic particles accounts for 25% of the total mass of the coating. All other aspects are the same as in Example 1.

[0182] Example 13

[0183] The difference between Example 13 and Example 1 is that the mass of the solid electrolyte powder accounts for 50% of the total mass of the coating, and the mass of the ceramic particles accounts for 45% of the total mass of the coating. All other aspects are the same as in Example 1.

[0184] Example 14

[0185] The difference between Example 14 and Example 1 is that the mass of the solid electrolyte powder accounts for 35% of the total mass of the coating, and the mass of the ceramic particles accounts for 60% of the total mass of the coating. All other aspects are the same as in Example 1.

[0186] Example 15

[0187] The difference between Example 16 and Example 1 is that the mass of the solid electrolyte powder accounts for 97% of the total mass of the coating, the mass of the ceramic particles accounts for 1% of the total mass of the coating, and the mass of the adhesive accounts for 2% of the total mass of the coating. All other aspects are the same as in Example 1.

[0188] Example 16

[0189] The difference between Example 16 and Example 1 is that the diaphragm includes two base membranes with a coating layer between them, and the outer surface of each diaphragm layer is coated. The material and thickness of the coating are the same as in Example 1, and everything else is the same as in Example 1.

[0190] Comparative Example 1

[0191] The difference between Comparative Example 1 and Example 1 is that the coating of the diaphragm is an inorganic coating. By mass, the slurry of the inorganic coating includes 95 parts of Al2O3 ceramic particles and 5 parts of PVDF binder. The thickness of the coating is 2 μm. All other aspects are the same as in Example 1.

[0192] Comparative Example 2

[0193] The difference between Comparative Example 2 and Example 1 is that the coating of the diaphragm is an inorganic coating. By mass, the slurry of the inorganic coating includes 95 parts of Al2O3 ceramic particles and 5 parts of PVDF binder. The thickness of the coating is 4 μm. All other aspects are the same as in Example 1.

[0194] Comparative Example 3

[0195] The difference between Comparative Example 3 and Example 1 is that the diaphragm coating is an inorganic coating. By mass, the inorganic coating slurry includes 95 parts of Al2O3 ceramic particles and 5 parts of PVDF binder. The coating thickness is 6 μm. All other aspects are the same as in Example 1.

[0196] Performance testing:

[0197] Coating thickness test: The cross-section was observed using laser cross-sectioning and SEM. Thickness was measured at three locations, and the average value was recorded as the coating thickness. The test results of each embodiment and comparative example are recorded in Table 1.

[0198] Membrane ionic conductivity test: A button cell was assembled by clamping the membrane with two stainless steel gaskets. Impedance was measured according to the national standard GB / T 36363-2018. The membrane ionic conductivity was calculated using the formula σ = L / RS, where σ is the membrane ionic conductivity, L is the membrane thickness, S is the area of ​​the stainless steel gaskets, and R is the measured impedance value. The test results for each embodiment and comparative example are recorded in Table 1.

[0199] Internal short circuit test: Under normal pressure and room temperature (25℃), using aluminum square-shell battery cells, charging and discharging were performed at 0% SOC to 100% SOC and a 1C rate current. The charge / discharge capacity for each charge / discharge cycle was calculated. If the charge / discharge capacity value was >1.05 for three consecutive cycles, it was determined to be an internal short circuit in the battery cell. The test results of each embodiment and comparative example are recorded in Table 1.

[0200] 5C discharge capacity retention rate test: Under normal pressure and room temperature (25℃), using an aluminum square hard shell, after charging to 100% with a current of 0.33C, discharge was performed with currents of 0.33C and 5C respectively. The 5C capacity / 0.33C capacity is the 5C discharge capacity retention rate. The test results of each embodiment and comparative example are recorded in Table 1.

[0201] Table 1. Parameters and performance data for each embodiment and comparative example.

[0202] As can be seen from the data in Table 1, compared with Comparative Examples 1-3, Examples 1-16 of this application, by reasonably adjusting the coating thickness of the separator, the type and content of solid electrolyte in the coating, and the number of coatings, have relatively high ionic conductivity of the separator. Thus, the sodium metal batteries without negative electrodes assembled therefrom all have good cycle resistance to internal short circuits and rate performance.

[0203] The above description is merely an exemplary embodiment of this application and does not limit the patent scope of this application. Any equivalent structural transformations made based on the technical concept of this application and the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A secondary battery, wherein, The membrane includes a base membrane and a coating disposed on at least one surface of the base membrane, the coating comprising a solid electrolyte; The solid electrolyte includes at least one of oxide solid electrolyte, sulfide solid electrolyte, borohydride solid electrolyte, and polymer solid electrolyte.

2. The secondary battery as described in claim 1, wherein, The content of the solid electrolyte in the coating is 35wt%-97wt%; and / or, The particle size of the solid electrolyte is 5nm-30nm.

3. The secondary battery as described in claim 1, wherein, The thickness of the coating is 0.5μm-20μm.

4. The secondary battery as described in claim 1, wherein, The ionic conductivity of the membrane is 0.3 ms / cm to 5 ms / cm.

5. The secondary battery as described in claim 1, wherein, The coating further includes ceramic particles, the content of which is 1wt%-73wt%; and / or, The coating also includes an adhesive, and the content of the adhesive in the coating is 2wt%-10wt%.

6. The secondary battery as described in claim 1, wherein, The base film is provided in two parts, and the coating is provided between the two base films and on the outer side of at least one of the base films.

7. The secondary battery as described in claim 1, wherein, The diaphragm further includes an adhesive layer disposed on the outside of the base film and / or the outside of the coating.

8. The secondary battery according to any one of claims 1 to 7, wherein, The secondary battery further includes a positive electrode sheet, which includes a positive electrode active material, and the positive electrode active material includes a sodium-containing active material. The solid electrolyte includes at least one of sodium alumina, sodium thiophosphate, sodium borohydride, sodium superionic conductor, and polyethylene oxide.

9. The secondary battery as described in claim 8, wherein, The secondary battery also includes a negative electrode sheet, which includes a negative current collector and a conductive coating disposed on at least one side surface of the negative current collector.

10. A diaphragm, wherein, The diaphragm includes a base membrane and a coating disposed on at least one side of the base membrane, the coating including a solid electrolyte; The solid electrolyte includes at least one of oxide solid electrolyte, sulfide solid electrolyte, borohydride solid electrolyte, and polymer solid electrolyte.

11. The diaphragm as claimed in claim 10, wherein, Meet any of the following conditions: The content of the solid electrolyte in the diaphragm is 35wt%-99wt%; The particle size of the solid electrolyte is 5nm-30nm; The thickness of the coating is 0.5μm-20μm; The ionic conductivity of the membrane is 0.3 ms / cm to 5 ms / cm; The coating also includes ceramic particles; The coating also includes an adhesive.

12. The diaphragm according to any one of claims 10 to 11, wherein, The base film is configured as two, and the coating is disposed between the two base films and on the outer side of at least one of the base films; and / or, The diaphragm further includes an adhesive layer disposed on the outside of the base film and / or the outside of the coating.

13. An electrical appliance, wherein, The electrical device includes a secondary battery as described in any one of claims 1 to 9.

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