Sodium-ion battery cell, battery and electric device

Abstract

A sodium-ion battery cell, a battery and an electric device. The sodium-ion battery cell comprises a positive electrode sheet and a negative electrode sheet which are oppositely arranged, wherein the positive electrode sheet contains a sodium layered metal oxide, the negative electrode sheet contains hard carbon, and the distance between the positive electrode sheet and the negative electrode sheet is 15-45 μm. The distance between a positive electrode sheet and a negative electrode sheet in a sodium-ion battery cell is set to be 15-45 μm, and the use of the distance range can allow a small amount of heat to be transferred to the positive electrode sheet after the negative electrode sheet, which contains hard carbon, generates heat, the transferred heat has little impact on the stability of a sodium layered metal oxide material in the positive electrode sheet, and the negative electrode sheet is not prone to rapidly accumulating heat. In this way, thermal runaway is unlikely to occur between the positive electrode sheet and the negative electrode sheet, so that the safety performance of sodium-ion batteries can be improved.

Description

Sodium ion battery cells, batteries and electrical devices

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 15, 2023, with application number 202311735640.2 and invention name “Sodium ion battery cell, battery and electrical device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the field of battery technology, and specifically relates to a sodium ion battery cell, a battery, and an electrical device. Background Art

[0003] Sodium-ion batteries (SIBs) are a new type of secondary battery whose cathode material is a sodium ion compound. Their high energy density and low cost have attracted considerable attention in the battery field. In recent years, SIBs have been increasingly used in electric vehicles and energy storage systems.

[0004] Typically, thermal runaway in lithium-ion batteries (LIBs) is triggered by oxygen release from the positive electrode, lithium deposition from the negative electrode, and meltdown and collapse of the separator. However, little research has been conducted on the thermal runaway mechanism in sodium-ion batteries, and it is generally known that thermal runaway can easily lead to safety issues.

[0005] Summary of the Invention

[0006] In view of the above problems, the present application provides a sodium ion battery cell, a battery and an electrical device, aiming to solve the technical problem of how to reduce the risk of thermal runaway of sodium ion batteries at low cost to improve their safety performance.

[0007] In a first aspect, an embodiment of the present application provides a sodium ion battery cell, comprising a positive electrode sheet and a negative electrode sheet arranged opposite to each other, wherein the positive electrode sheet contains sodium layered metal oxide, and the negative electrode sheet contains hard carbon; the spacing between the positive electrode sheet and the negative electrode sheet is 15-45 μm.

[0008] The present application discovered that when a sodium-ion battery cell is charged to a SOC greater than 50%, the accumulated heat generated by the reaction between the sodium metal in the negative electrode plate and the electrolyte will continue to rise in temperature, which may trigger the sodium layered metal oxide material in the positive electrode plate to react and release oxygen, accelerating thermal runaway of the sodium-ion battery cell; therefore, the present application sets the spacing between the positive electrode plate and the negative electrode plate to 15-45 μm. Utilizing this spacing range, a small amount of heat can be transferred to the positive electrode plate after the negative electrode plate is heated, making it less likely for thermal runaway between the positive and negative electrode plates, thereby improving the safety performance of the sodium-ion battery.

[0009] In some embodiments, the sodium layered metal oxide has a sodium removal capacity of 100 to 200 mAh / g, and a coating surface density of the sodium layered metal oxide of 0.01 to 0.04 g / cm 2 .

[0010] In some embodiments, the sodium storage capacity of the hard carbon is 200-400 mAh / g, and the coating surface density of the hard carbon is 0.005-0.02 g / cm 2 .

[0011] In some embodiments, the sodium layered metal oxide has a sodium removal gram capacity of 140 to 170 mAh / g, and the hard carbon has a sodium storage gram capacity of 300 to 370 mAh / g.

[0012] The sodium ion battery monomer formed by the combination of the positive electrode formed by the sodium layered metal oxide with the above-mentioned sodium-free gram capacity and the negative electrode formed by the hard carbon with the above-mentioned sodium-storing gram capacity can make the battery have better charge and discharge performance and safety performance.

[0013] In some embodiments, a separator is provided between the positive electrode sheet and the negative electrode sheet, and a thickness of the separator is less than or equal to the distance between the positive electrode sheet and the negative electrode sheet.

[0014] By providing a separator of a certain thickness between the positive electrode sheet and the negative electrode sheet, the required distance between the positive electrode sheet and the negative electrode sheet can be maintained.

[0015] In some embodiments, the sodium ion battery cell further includes an electrolyte, and the electrolyte includes a carbonate solvent.

[0016] Carbonate solvents are low in toxicity, environmentally friendly, and have excellent oxidation resistance and stability when in contact with the negative electrode. Therefore, such electrolytes exhibit excellent electrochemical stability when used in sodium-ion battery cells. Combined with the aforementioned minimum spacing between the positive and negative electrode sheets, this can further extend the battery life.

[0017] In a second aspect, an embodiment of the present application provides a battery comprising at least two sodium ion battery cells provided in the first aspect of the present application.

[0018] Based on the use of the sodium ion battery cells of the embodiments of the present application, such batteries are not prone to thermal runaway and thus have excellent safety performance.

[0019] In a third aspect, an embodiment of the present application provides an electrical device, which includes the sodium ion battery cell provided in the first aspect of the present application, or the battery provided in the second aspect of the present application.

[0020] By adopting the sodium ion battery cell or battery provided in the embodiments of the present application, such an electrical device is not prone to thermal runaway, has good safety, and can work for a longer time.

[0021] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0023] FIG1 is a schematic structural diagram of an embodiment of a sodium ion battery cell according to an embodiment of the present application;

[0024] FIG2 is an exploded schematic diagram of the sodium ion battery cell shown in FIG1 ;

[0025] FIG3 is a schematic structural diagram of an embodiment of a battery module according to the present application;

[0026] FIG4 is a schematic structural diagram of an embodiment of a battery pack according to the present application;

[0027] FIG5 is a schematic diagram of the exploded structure of the battery pack shown in FIG4 ;

[0028] FIG6 is a schematic diagram of an embodiment of an electrical device including a sodium ion battery cell according to an embodiment of the present application as a power source.

[0029] Description of reference numerals:

[0030] 10 - sodium-ion battery cell; 11 - shell; 12 - top cover assembly; 13 - electrode assembly; 20 - battery module; 30 - battery pack; 31 - upper box; 32 - lower box. DETAILED DESCRIPTION

[0031] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0033] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0034] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0035] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0036] In the description of the embodiments of this application, the term "plurality" refers to two or more (including two). Similarly, "multiple groups" refers to two or more (including two groups), and "multiple sheets" refers to two or more (including two sheets). "At least one" refers to more than one (including one, two, three, etc.).

[0037] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0038] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0039] With the increasing depletion of traditional energy resources, the development of new energy storage devices is gaining increasing attention. Secondary batteries, in particular, have attracted significant attention due to their high energy density, high theoretical capacity, excellent cycle stability, and environmentally friendly properties. Secondary batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles. As the application areas of secondary batteries as power batteries continue to expand, their market demand is also growing, and the requirements for battery performance, such as cycle performance, are becoming increasingly stringent.

[0040] Lithium-ion batteries, a type of secondary battery, boast high energy density, long lifespan, and energy conservation and environmental friendliness. However, due to global lithium resource limitations and rising costs, their application in large-scale energy storage presents challenges. Sodium-ion batteries, with their advantages such as abundant sodium reserves, low cost, and unique battery safety characteristics, have become a key candidate for large-scale energy storage systems. Therefore, the development of resource-free, low-cost sodium-ion batteries holds great potential in the energy storage field.

[0041] The operating principle of sodium-ion batteries is similar to that of lithium-ion batteries, both achieving charge and discharge through ion exchange between positive and negative electrodes. For example, a sodium-ion battery consists of positive and negative electrodes, along with an electrolyte and a separator located between them. For sodium-ion batteries, the energy per unit volume varies depending on the material system used. Due to the increased weight of sodium, the energy density of sodium-ion batteries is generally lower than that of lithium-ion batteries. To further increase the energy density of sodium-ion batteries, a higher energy density material system is often used. This increases the amount of heat generated, making it easy for heat transfer between the electrodes to become uncontrolled, leading to safety concerns.

[0042] Currently, there is little research on the thermal runaway mechanism of sodium-ion batteries. However, it is known that thermal runaway of lithium-ion battery systems is mainly caused by three reasons: oxygen release from the positive electrode, lithium deposition at the negative electrode, and breakdown of the separator. For normal or fresh lithium-ion batteries, lithium deposition rarely occurs at the negative electrode, so this factor has little impact on normal lithium-ion batteries. However, if a ternary positive electrode material is used for the positive electrode, a 200°C thermal abuse test found that the positive electrode will release a large amount of oxygen and heat under this thermal abuse temperature condition. At the same time, the solid electrolyte interphase (SEI) film of the negative electrode is almost destroyed by the heat, causing the lithium metal and the electrolyte to react. However, it should be noted that because the negative electrode of the lithium-ion battery is a lithium intercalation mechanism, when the SEI film is destroyed, the lithium metal generally does not melt out quickly to react with the electrolyte, that is, the negative electrode reaction is relatively not very intense. As for the separator, safety is very important. If it melts due to heat, it can easily cause the positive and negative electrodes to overlap, thereby increasing heat generation.

[0043] However, when the inventors of this application were studying sodium-ion batteries, they found that the factors affecting their thermal runaway are very different from those of lithium-ion batteries. Although the mechanism is not yet fully understood, one reason is that after charging, especially when the sodium-ion battery is in a charging state greater than 50% SOC (State of Charge), a large amount of metallic sodium at the negative electrode fills pores in the hard carbon. When the battery reaches a certain temperature (about 130°C), the SEI film formed on the surface of the negative electrode begins to break down, and the heat will accumulate and heat up rapidly, triggering chemical reactions on the positive electrode side. Therefore, it is necessary to dissipate the heat generated by the negative electrode as soon as possible.

[0044] Based on the above understanding, to address the safety issues of sodium-ion batteries, the present invention combines theoretical calculations with experiments. Based on the sodium storage mechanism of the negative electrode sheet, a minimum spacing is set between the negative and positive electrode sheets in the sodium-ion battery. This can not only dissipate some of the heat generated by the negative electrode sheet early, but also effectively prevent the heat from the negative electrode side from affecting the positive electrode, thereby achieving sodium ion safety at a low cost. Therefore, the following technical solution is proposed.

[0045] Sodium-ion battery cells

[0046] In a first aspect, an embodiment of the present application provides a sodium-ion battery cell, comprising a positive electrode sheet and a negative electrode sheet disposed opposite to each other. The sodium-ion battery cell of the embodiment of the present application has the following two characteristics: (1) the positive electrode sheet contains a sodium layered metal oxide, and the negative electrode sheet contains hard carbon; because the sodium storage mechanism of the negative electrode sheet of a sodium-ion battery is different from the lithium insertion mechanism of the negative electrode of a lithium-ion battery, and the melting point of sodium metal is approximately 97°C, the SEI film of the negative electrode sheet generally begins to be destroyed starting at 130°C. Therefore, after charging, the sodium metal stored in the negative electrode sheet of the sodium-ion battery can be melted out and react with the electrolyte under conditions above 130°C. (2) Based on the above characteristics, the spacing between the positive electrode sheet and the negative electrode sheet is set to 15-45 μm. When the sodium ion battery abnormality causes the negative electrode sheet to start heating, this spacing range can be used to transfer part of the heat of the negative electrode sheet to the positive electrode sheet. Moreover, the transferred heat is small, which has little impact on the sodium layered metal oxide. At the same time, the negative electrode sheet is not easy to accumulate heat quickly, so that thermal runaway is not easy between the positive electrode sheet and the negative electrode sheet, thereby improving the safety performance of the sodium ion battery.

[0047] It should be noted that the spacing between the positive electrode sheets and the negative electrode sheets mentioned in the embodiments of the present application refers to the spacing between adjacent positive electrode sheets and negative electrode sheets in the electrode assembly, that is, the spacing between the two opposite surfaces of adjacent positive electrode sheets and negative electrode sheets. The electrode assembly can be in various forms such as winding and / or stacking. The spacing between adjacent positive electrode sheets and negative electrode sheets is at least 15μm, for example, it can be 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 22μm, 25μm, 28μm, 30μm, 32μm, 35μm, 38μm, 40μm, 45μm, etc.

[0048] In the embodiments of the present application, the thickness between adjacent positive and negative electrode sheets of a sodium-ion battery cell is 15 to 45 μm, which enables the sodium-ion battery cell to have both good safety performance and high volumetric energy density. The positive electrode sheet comprises a sodium layered metal oxide, and the negative electrode sheet comprises a hard carbon. Sodium layered metal oxides, used as positive electrode active materials for sodium-ion batteries, have the characteristics of high specific capacity and high compaction density. However, abnormal heating of sodium-ion batteries can easily cause the sodium metal oxide to release lattice oxygen. These lattice oxygen reacts with hydrogen ions in the battery to form water molecules, which easily react with elemental sodium generated in the negative electrode sheet to release heat. Hard carbon, used as the negative electrode active material for sodium-ion batteries, has the advantages of low operating potential and high capacity. In addition, in sodium-ion batteries, the mechanism for storing sodium in hard carbon involves a large amount of sodium metal filling the pores, which is significantly different from the lithium embedding mechanism of the negative electrode of lithium-ion batteries. For example, when the sodium-ion battery is above 50% SOC, the sodium storage mechanism of hard carbon is mainly a pore filling mechanism (i.e., sodium metal fills the pores in large quantities).

[0049] Based on this, the embodiment of the present application uses sodium layered metal oxide as the positive electrode active material of the positive electrode sheet of the sodium ion battery, and hard carbon as the negative electrode active material of the negative electrode sheet of the sodium ion battery. At the same time, a certain distance between the positive electrode sheet and the negative electrode sheet is maintained (i.e., 15 to 45 μm). This not only fully utilizes the advantages of the above-mentioned active materials, but also makes it difficult for the positive electrode sheet and the negative electrode sheet to experience thermal runaway, and has good safety.

[0050] In some embodiments, the sodium layered metal oxide has a sodium removal capacity of 100 to 200 mAh / g, and a coating surface density of the sodium layered metal oxide is 0.01 to 0.04 g / cm 2 The sodium storage capacity of hard carbon is 200-400 mAh / g, and the coating surface density of hard carbon is 0.005-0.02 g / cm 2 .

[0051] For example, the sodium layered metal oxide can have a sodium removal capacity of 100 mAh / g, 150 mAh / g, 170 mAh / g, 200 mAh / g, etc., and a coating surface density of 0.01 g / cm 2 , 0.02g / cm 2 , 0.03g / cm 2 , 0.04g / cm 2 The sodium storage capacity of hard carbon can be 200mAh / g, 250mAh / g, 3000mAh / g, 400mAh / g, etc., and the coating surface density can be 0.005g / cm 2 , 0.01g / cm 2 , 0.015g / cm 2 , 0.02g / cm 2 wait.

[0052] The per-area capacity of the positive electrode of a sodium-ion battery cell is equal to the sodium-removed gram capacity of the sodium layered metal oxide multiplied by the coating area density of the sodium layered metal oxide. The sodium-removed gram capacity is the sodium-removed capacity per unit weight of the positive electrode active material during charge and discharge of the sodium-ion battery cell, and the coating area density is the weight of the sodium-ion battery positive electrode active material coated per unit area on a single surface of the positive electrode current collector. The per-area capacity of the negative electrode is equal to the sodium-storage gram capacity of the hard carbon multiplied by the coating area density of the hard carbon. The sodium-storage gram capacity is the sodium-storage capacity per unit weight of the negative electrode active material during charge and discharge of the sodium-ion battery cell, and the coating area density is the weight of the negative electrode active material coated per unit area on a single surface of the negative electrode current collector.

[0053] The product of the gram capacity and the coating surface density can obtain the corresponding electrode unit area capacity, and the electrode unit area capacity value is related to the heat generation energy of the sodium ion battery cell. Therefore, the above-mentioned sodium removal gram capacity and coating surface density parameters can be set for the sodium layered metal oxide of the positive electrode, and the above-mentioned sodium storage gram capacity and coating surface density parameters can be set for the hard carbon of the negative electrode. This not only improves the charge and discharge performance of the battery, but also the sodium ion battery cell with the above parameters is not prone to thermal runaway, so that the battery has good safety.

[0054] In some embodiments, the sodium-layered metal oxide has a sodium-free gram capacity of 140 to 170 mAh / g, and the hard carbon has a sodium-storage gram capacity of 300 to 370 mAh / g. A sodium-ion battery cell formed by combining a positive electrode sheet formed from the sodium-layered metal oxide with a high sodium-free gram capacity and a negative electrode sheet formed from the hard carbon with a high sodium-storage gram capacity can provide both improved charge-discharge performance and safety.

[0055] In some embodiments, a separator is provided between the positive electrode sheet and the negative electrode sheet, and the thickness of the separator is less than or equal to the distance between the positive electrode sheet and the negative electrode sheet.

[0056] Specifically, a separator is stacked between the positive and negative electrodes, with a thickness of 15 to 45 μm. Sodium-ion battery cells have good safety performance, low internal resistance, and high energy density.

[0057] The material of the separator can be a single-layer separator or a composite separator. The material of the separator can be one or more of polyethylene, polypropylene, polyvinylidene fluoride, cellulose, fluoropolymer, etc., and their multi-layer composite films. The surface of the separator can be coated or uncoated, as long as the above-mentioned required spacing between the positive electrode sheet and the negative electrode sheet can be achieved. That is, by providing a separator of a certain thickness between the positive electrode sheet and the negative electrode sheet, the required spacing between the positive electrode sheet and the negative electrode sheet can be maintained.

[0058] In some embodiments, the sodium-ion battery cells are injected with an electrolyte comprising a carbonate solvent. Carbonate solvents are low in toxicity, environmentally friendly, and have excellent oxidation resistance and good stability when in contact with the negative electrode. Therefore, such an electrolyte has excellent electrochemical stability when used in sodium-ion battery cells. Combined with the minimum spacing between the positive and negative electrode plates described above, the battery life can be further extended.

[0059] Specifically, the electrolyte includes an electrolyte sodium salt and a carbonate solvent. The electrolyte sodium salt plays the role of conducting ions between the positive electrode plate and the negative electrode plate. The electrolyte sodium salt can be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonylimide, sodium difluorophosphate, and sodium difluorooxalatoborate. The carbonate solvent in the electrolyte can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, and fluoroethylene carbonate.

[0060] In some embodiments, the electrolyte may further include additives. For example, the additives may include film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, or additives that improve battery high or low temperature performance.

[0061] In some embodiments, a positive electrode sheet of a sodium ion battery cell includes a positive electrode current collector and a positive electrode active material layer bonded to at least one surface of the positive electrode current collector.

[0062] In some embodiments, the positive electrode 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 material base layer and a metal layer formed on at least one surface of the polymer material base layer. 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 material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0063] In some embodiments, the positive electrode active material layer includes a sodium ion battery positive electrode active material, specifically, a sodium layered metal oxide, which may mainly include a sodium layered metal oxide (Na x MO2, M = Fe, Mn, Ni, Co, Cr and combinations thereof), such as layered sodium nickel cobalt aluminum oxide (NCA), sodium nickel cobalt manganese oxide (NCM) and sodium iron phosphate (NASICON). By selecting the positive active material for the sodium ion battery, it has a certain capacity per unit area and is conducive to preventing thermal runaway within the parameter range set in the embodiment of the application.

[0064] In some embodiments, the positive electrode active material layer may further optionally include a binder and a conductive agent. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0065] In some embodiments, a negative electrode sheet of a sodium ion battery cell includes a negative electrode current collector and a negative electrode active material layer bonded to at least one surface of the negative electrode current collector.

[0066] In some embodiments, the negative electrode 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 material base layer and a metal layer formed on at least one surface of the polymer material base layer. 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 material substrate such as polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.

[0067] In some embodiments, the negative electrode active material layer includes a negative electrode active material, specifically, hard carbon. The negative electrode active material of the sodium ion battery is selected to have a certain capacity per unit area.

[0068] In some embodiments, the negative electrode active material layer may further optionally include a binder and a conductive agent. As an example, the binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0069] It should be noted that the positive electrode current collector and the negative electrode current collector have two surfaces opposite to each other in the direction of their own thickness, and the positive electrode active material layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector, and the negative electrode active material layer is arranged on any one or both of the two opposite surfaces of the negative electrode current collector. The various parameters given in the embodiments of the present application (such as gram capacity, surface density, unit area capacity, etc.) refer to the parameters of the active material layer on one side of the positive electrode current collector or the negative electrode current collector, for example, it can be the parameters of the active material layer opposite to the isolation membrane. When the positive electrode active material layer is arranged on both sides of the positive electrode current collector, the parameters of the positive electrode active material layer on either side meet the requirements of this application, that is, it is considered to fall within the protection scope of this application. When the negative electrode active material layer is arranged on both sides of the negative electrode current collector, the parameters of the negative electrode active material layer on either side meet the requirements of this application, that is, it is considered to fall within the protection scope of this application.

[0070] In some embodiments, a sodium-ion battery cell refers to a battery housing and an electrode assembly encapsulated within the battery housing. The shape of a sodium-ion battery cell is not particularly limited and can be cylindrical, square, or any other shape. A square sodium-ion battery cell 10 is shown in FIG1 .

[0071] In some embodiments, as shown in Figure 2, the outer packaging of the sodium ion battery cell 10 may include a shell 11 and a top cover assembly 12. The shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the top cover assembly 12 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the isolation membrane and the negative electrode sheet contained in the sodium ion battery cell of the embodiment of the present application can be formed into an electrode assembly 13 through a winding process and / or a lamination process. The electrode assembly 13 is encapsulated in the receiving cavity. For liquid sodium ion battery cells, the electrolyte is infiltrated in the electrode assembly 13. The number of electrode assemblies 13 contained in the sodium ion battery cell 10 can be one or more, which can be adjusted according to actual needs.

[0072] The preparation method of a sodium-ion battery cell 10 is well known. In some embodiments, using a liquid sodium-ion battery unit as an example, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a sodium-ion battery cell 10. For example, the positive electrode sheet, separator, and negative electrode sheet can be wound or laminated to form an electrode assembly 13. The electrode assembly 13 is placed in an outer package, dried, and then injected with electrolyte. The sodium-ion battery cell 10 is then vacuum packaged, allowed to stand, formed, and shaped.

[0073] In a second aspect, embodiments of the present application provide a battery comprising the sodium-ion battery cell provided in the first aspect of the present application. Based on the sodium-ion battery cell of the embodiments of the present application, such a battery is not prone to thermal runaway, thus having excellent safety performance.

[0074] In some embodiments, the battery of the present application is a secondary battery, which may include any one of a battery cell, a battery module, and a battery pack.

[0075] The battery module is assembled from the sodium ion battery cells 10 , that is, it may contain a plurality of the sodium ion battery cells 10 , and the specific number can be adjusted according to the application and capacity of the battery module.

[0076] In some embodiments, FIG3 is a schematic diagram of an exemplary battery module 20. As shown in FIG3 , in the battery module 20, multiple sodium-ion battery cells 10 may be arranged sequentially along the length of the battery module 20. Of course, they may also be arranged in any other manner. Furthermore, the multiple sodium-ion battery cells 10 may be secured by fasteners. Optionally, the battery module 20 may further include a housing having a storage space, wherein the multiple sodium-ion battery cells 10 are accommodated in the storage space.

[0077] A battery pack is assembled from the aforementioned sodium-ion battery cells 10, i.e., it may contain multiple sodium-ion battery cells 10, wherein multiple sodium-ion battery cells 10 can be assembled into the aforementioned battery module 20. The specific number of sodium-ion battery cells 10 or battery modules 20 contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0078] In the embodiment, Figures 4 and 5 are schematic diagrams of an exemplary battery pack 30. The battery pack 30 may include a battery box and multiple battery modules 20 disposed within the battery box. The battery box includes an upper box body 31 and a lower box body 32. The upper box body 31 covers the lower box body 32 and forms an enclosed space for accommodating the battery modules 20. The multiple battery modules 20 may be arranged in any manner within the battery box.

[0079] Electrical devices

[0080] Thirdly, embodiments of the present application further provide an electrical device comprising a sodium-ion battery cell or battery according to the embodiments of the present application. The sodium-ion battery cell or battery can serve as a power source or energy storage unit for the electrical device. Based on the advantages of the sodium-ion battery according to the embodiments of the present application, such an electrical device is less susceptible to thermal runaway, exhibits excellent safety, and can operate for a longer period of time.

[0081] Power-consuming devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc. The power-consuming devices may use battery cells, battery modules, or battery packs based on their usage requirements.

[0082] Figure 6 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 may be used.

[0083] 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 sodium ion battery as a power source.

[0084] Example

[0085] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0086] Example 1

[0087] A battery cell, a liquid sodium ion battery cell, includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The specific preparation steps are as follows:

[0088] Positive electrode preparation:

[0089] Using methyl pyrrolidone (NMP) as a solvent, layered sodium nickel cobalt aluminum oxide, conductive carbon black, and polyvinylidene fluoride binder were mixed and dissolved in the solvent at a mass ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was evenly coated on aluminum foil, double-sided coating was performed, and after sufficient vacuum drying, cold pressing, and slitting, the positive electrode sheets were obtained. The surface density of each single-sided layered sodium nickel cobalt aluminum oxide is 0.02g / cm 2 , and the sodium removal capacity of layered sodium nickel cobalt aluminum oxide is 150mAh / g.

[0090] Negative electrode preparation:

[0091] Using water as a solvent, hard carbon active material, conductive carbon black, and carboxymethyl cellulose binder are mixed and dissolved in the solvent at a mass ratio of 95:2:3 to prepare a negative electrode slurry. The negative electrode slurry is evenly coated on aluminum foil, double-sided coating is performed, and after sufficient vacuum drying, cold pressing, and slitting, the positive electrode sheet is obtained. The surface density of each single side of the hard carbon active material is 0.01g / cm 2 , and the sodium embedding capacity of the hard carbon active material is 330mAh / g.

[0092] Electrolyte: Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1 at room temperature, and NaPF6 was added to the mixed solution to obtain a solution with a concentration of 1 mol / L as the electrolyte.

[0093] Separator film: Polypropylene separator, thickness 20 μm.

[0094] Secondary battery assembly: In a constant temperature room, in an argon atmosphere glove box, the positive and negative electrodes prepared above were stacked in the order of "positive electrode - separator - negative electrode", filled with electrolyte, and assembled into button-type sodium ion battery cells. The full charge voltage K was 4V, and the unit area capacity of the negative electrode was the largest unit area capacity X = 3.3mAh / cm 2 .

[0095] Example 2

[0096] The difference from Example 1 is:

[0097] The thickness of the isolation film is 30 μm, and the other aspects are the same as those in Example 1.

[0098] Example 3

[0099] The difference from Example 1 is:

[0100] The thickness of the isolation film is 40 μm, and the other aspects are the same as those in Example 1.

[0101] Example 4

[0102] The difference from Example 1 is:

[0103] The thickness of the isolation film is 45 μm, and the other aspects are the same as those in Example 1.

[0104] Example 5

[0105] The difference from Example 1 is:

[0106] The sodium-free gram capacity of layered sodium nickel cobalt aluminum oxide is 170 mAh / g and the surface density is 0.02 g / cm 2 The hard carbon active material has a sodium embedding capacity of 350 mAh / g and a surface density of 0.01 g / cm 2 ; The negative electrode has a larger unit area capacity X = 3.5 mAh / cm 2 ; The thickness of the isolation film is 21μm, and the rest are the same as in Example 1.

[0107] Example 6

[0108] The difference from Example 5 is:

[0109] The thickness of the isolation film is 30 μm, and the other aspects are the same as those in Example 5.

[0110] Example 7

[0111] The difference from Example 5 is:

[0112] The thickness of the isolation film is 35 μm, and the other aspects are the same as those in Example 5.

[0113] Example 8

[0114] The difference from Example 5 is:

[0115] The thickness of the isolation film is 45 μm, and the other aspects are the same as those in Example 5.

[0116] Example 9

[0117] The difference from Example 1 is:

[0118] The sodium-free gram capacity of layered sodium nickel cobalt aluminum oxide is 100 mAh / g and the surface density is 0.01 g / cm 2 The hard carbon active material has a sodium embedding capacity of 200 mAh / g and a surface density of 0.01 g / cm 2 ; The negative electrode has a larger unit area capacity X = 2 mAh / cm 2 ; The thickness of the isolation film is 15μm, and the rest are the same as in Example 1.

[0119] Example 10

[0120] The difference from Example 1 is:

[0121] The sodium-free gram capacity of layered sodium nickel cobalt aluminum oxide is 200 mAh / g and the surface density is 0.02 g / cm 2 The hard carbon active material has a sodium embedding capacity of 200 mAh / g and a surface density of 0.006 g / cm 2 ; The negative electrode has a larger unit area capacity X = 2.4 mAh / cm 2 ; The thickness of the isolation film is 15μm, and the rest are the same as in Example 1.

[0122] Comparative Example 1

[0123] The difference from Example 1 is:

[0124] The thickness of the isolation film is 14 μm, and the other aspects are the same as those in Example 1.

[0125] Comparative Example 2

[0126] The difference from Example 1 is:

[0127] The thickness of the isolation film is 14 μm, and the other aspects are the same as those in Example 5.

[0128] Comparative Example 3

[0129] The difference from Example 5 is:

[0130] The thickness of the isolation film is 14 μm, and the other aspects are the same as those in Example 9.

[0131] Comparative Example 4

[0132] The difference from Example 5 is:

[0133] The thickness of the isolation film is 14 μm, and the other aspects are the same as those in Example 10.

[0134] Performance Testing

[0135] The sodium ion battery cells of the above examples and comparative examples were tested separately.

[0136] Security testing steps include:

[0137] An 80W (heating resistor) heat source is applied to the electrode assembly of the sodium-ion battery cell; the valve opening time is detected; the explosion-proof valve opening time of the electrode assembly is detected under a thermal overload test temperature of 200°C. This time reflects the severity of thermal runaway gas production inside the battery. The longer the time, the safer it is.

[0138] The test results of the above sodium ion battery are shown in Table 1.

[0139] Table 1

[0140] It can be seen from Table 1 that for sodium-ion battery cells, under certain conditions of unit area capacity and full charge voltage, the thickness of the isolation film stacked between the positive electrode sheet and the negative electrode sheet is 15 to 45 μm, which is not prone to thermal runaway and has good safety.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A sodium ion battery cell, comprising a positive electrode sheet and a negative electrode sheet arranged opposite to each other, wherein: The positive electrode plate contains sodium layered metal oxide, and the negative electrode plate contains hard carbon; The distance between the positive electrode sheet and the negative electrode sheet is 15-45 μm.

2. The sodium ion battery cell according to claim 1, wherein: The sodium layered metal oxide has a sodium removal capacity of 100 to 200 mAh / g, and a coating surface density of 0.01 to 0.04 g / cm 2 .

3. The sodium ion battery cell according to claim 1 or 2, wherein: The sodium storage capacity of the hard carbon is 200-400 mAh / g, and the coating surface density of the hard carbon is 0.005-0.02 g / cm 2 .

4. The sodium ion battery cell according to claim 3, wherein: The sodium-removing gram capacity of the sodium layered metal oxide is 140 to 170 mAh / g, and the sodium-storing gram capacity of the hard carbon is 300 to 370 mAh / g.

5. The sodium ion battery cell according to any one of claims 1 to 4, wherein: A separator is provided between the positive electrode sheet and the negative electrode sheet, and a thickness of the separator is less than or equal to a distance between the positive electrode sheet and the negative electrode sheet.

6. The sodium ion battery cell according to any one of claims 1 to 5, wherein: The sodium ion battery cell further includes an electrolyte, and the electrolyte includes a carbonate solvent.

7. A battery, wherein: Comprising at least two sodium ion battery monomers according to any one of claims 1 to 6.

8. An electrical device, wherein: The electrical device comprises the sodium ion battery cell according to any one of claims 1 to 6, or the battery according to claim 7.

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