Positive electrode material, positive electrode sheet, secondary battery, and electric device

Abstract

The application relates to the technical field of batteries, and relates to a positive electrode material, a positive electrode sheet, a secondary battery and a power utilization device. The secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode material, the positive electrode material comprises a sulfur material and a conductive porous carrier, the sulfur material is adsorbed in the pores of the conductive porous carrier, and the pores of the conductive porous carrier are composed of micropores and mesopores. The technical scheme of the application can improve the cycle performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a positive electrode material, a positive electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] Secondary batteries are a type of battery that uses sulfur or sulfur-containing compounds as the positive electrode material. Because sulfur or sulfur-containing compounds have relatively poor conductivity, the positive electrode material needs to incorporate a conductive porous carrier. In related technologies, secondary batteries often exhibit a shuttle effect, resulting in poor cycle performance. Summary of the Invention

[0003] The main objective of this application is to provide a positive electrode material, a positive electrode sheet, a secondary battery, and an electrical device, with the aim of improving the cycle performance of the secondary battery.

[0004] To achieve the above objectives, the first aspect of this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode material, the positive electrode material including a sulfur material and a conductive porous carrier, the sulfur material being adsorbed within the pores of the conductive porous carrier, the pores of the conductive porous carrier being composed of micropores and mesopores.

[0005] In the secondary battery provided in this application, the positive electrode material adopts a conductive porous carrier composed of micropores and mesopores, which can physically and chemically confine the sulfur material, greatly limiting the shuttle effect of the sulfur material during the charging and discharging process of the secondary battery, thereby improving the cycle performance of the secondary battery.

[0006] In one embodiment, the average pore size of the conductive porous carrier is 2nm-4nm.

[0007] This application limits the average pore size of the conductive porous carrier to a suitable range, which is beneficial for achieving physicochemical confinement of sulfur materials, suppressing the shuttle effect, and at the same time ensuring a relatively high sulfur material loading.

[0008] In one embodiment, the total pore volume of the conductive porous carrier is 0.1 cm³. 3 / g-1cm 3 / g.

[0009] This application limits the total pore volume of the conductive porous carrier to a suitable range, which is beneficial for achieving physicochemical confinement of sulfur materials, suppressing the shuttle effect, and ensuring a relatively high sulfur material loading. By adjusting the pore volume of the conductive porous carrier, this application can control the loading of sodium sulfide, thereby optimizing the electronic conductivity and ion diffusion of the electrode material and improving the electrochemical performance of the secondary battery.

[0010] In one embodiment, the conductive porous support comprises a microporous carbon support.

[0011] The conductive porous support of this application adopts a micro-mesoporous carbon support. The micro-mesoporous carbon support has a high specific surface area and porosity, which is beneficial to the loading and physical confinement of sulfur materials. In addition, the micro-mesoporous carbon support has good conductivity, which can effectively transfer electrons during the charging and discharging process of secondary batteries and has good electrochemical performance. At the same time, the micro-mesoporous carbon support has high chemical stability, strong controllability and strong adsorption capacity, which is beneficial to improving the sulfur loading and cycle stability of sulfur materials.

[0012] In one embodiment, the microporous carbon support includes at least one of nitrogen-doped microporous carbon, nitrogen-doped microporous carbon derived from metal-organic frameworks, ordered microporous carbon, and microporous activated carbon.

[0013] Nitrogen-doped micro-mesoporous carbon and nitrogen-doped micro-mesoporous carbon derived from metal-organic frameworks possess both microporous and mesoporous structures, exhibiting high specific surface area and porosity, which is beneficial for the adsorption of sulfur in materials. Nitrogen doping can improve the conductivity of materials, which is conducive to achieving high specific capacity and good cycle performance in secondary batteries.

[0014] Ordered micro-mesoporous carbon possesses a highly ordered pore structure with regular and uniform pore arrangement, which facilitates electrolyte penetration and ion transport, increasing the rate of electrode reactions and thus achieving high capacity. Simultaneously, the presence of micropores and mesopores in ordered micro-mesoporous carbon results in a high specific surface area, which is beneficial for the adsorption of sulfur materials.

[0015] Microporous activated carbon possesses both microporous and mesoporous structures, exhibiting high specific surface area and porosity, which is beneficial for the adsorption of sulfur materials.

[0016] In one embodiment, the mass ratio of the sulfur material to the conductive porous carrier is 0.5:3 to 2.5:3.

[0017] This application selects an appropriate mass ratio of sulfur material and conductive porous carrier, which can better adsorb and disperse sulfur material, increase the sulfur material loading, thereby improving cycle performance, and also increase the theoretical specific capacity of secondary battery.

[0018] In one embodiment, the sulfur material includes sodium sulfide. The secondary battery of this application is a sodium sulfide battery, which has the advantages of low cost and high theoretical energy density. The conductive porous carrier used in the positive electrode material has pores composed of a mixture of micropores and mesopores, which can effectively suppress the aforementioned shuttle effect and improve the capacity and cycle performance of the sodium sulfide battery.

[0019] A second aspect of this application also provides a positive electrode material, comprising a sulfur material and a conductive porous carrier, wherein the sulfur material is adsorbed within the pores of the conductive porous carrier, and the pores of the conductive porous carrier are composed of micropores and mesopores.

[0020] In one embodiment, the average pore size of the conductive porous carrier is 2nm-4nm.

[0021] In one embodiment, the total pore volume of the conductive porous carrier is 0.1 cm³. 3 / g-1cm 3 / g.

[0022] In one embodiment, the conductive porous support comprises a microporous carbon support.

[0023] In one embodiment, the microporous carbon support includes at least one of nitrogen-doped microporous carbon, nitrogen-doped microporous carbon derived from metal-organic frameworks, ordered microporous carbon, and microporous activated carbon.

[0024] In one embodiment, the mass ratio of the sulfur material to the conductive porous carrier is 0.5:3 to 2.5:3.

[0025] A third aspect of this application also provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive active material layer includes the positive electrode material provided in the second aspect of this application.

[0026] The fourth aspect of this application also provides an electrical device, which includes the secondary battery provided in the first aspect of this application.

[0027] The secondary battery provided in this application has a positive electrode material comprising sulfur material and a conductive porous carrier. The sulfur material is adsorbed within the pores of the conductive porous carrier, which consists of micropores and mesopores. By employing a conductive porous carrier with pores composed of micropores and mesopores, the sulfur material can be physically and chemically confined, greatly limiting the shuttle effect of the sulfur material during the charging and discharging process of the secondary battery, thereby improving the cycle performance of the secondary battery. Attached Figure Description

[0028] 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.

[0029] Figure 1 The nitrogen adsorption-desorption curves of nitrogen-doped microporous carbon derived from ZIF-8 in Example 1 of this application are shown.

[0030] Figure 2 The nitrogen adsorption-desorption curves for ordered microporous carbon in Example 2 of this application are shown.

[0031] Figure 3 This is a scanning electron microscope image of the nitrogen-doped microporous carbon derived from ZIF-8 in Example 1 of this application;

[0032] Figure 4 This is a schematic diagram of the structure of an embodiment of the secondary battery provided in this application;

[0033] Figure 5 This is an exploded structural diagram of an embodiment of the secondary battery provided in this application.

[0034] Explanation of icon numbers:

[0035] 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover plate.

[0036] 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

[0037] 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.

[0038] The following detailed description, with appropriate reference to the accompanying drawings, discloses the positive electrode material, its preparation method, the positive electrode sheet, 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 providing a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0039] 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.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0042] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates 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.

[0043] Sulfur-based secondary batteries are a type of secondary battery that uses sulfur or sulfur-containing compounds as the positive electrode material. Because sulfur or sulfur-containing compounds have relatively poor conductivity, a conductive porous carrier needs to be added to the positive electrode material. In related technologies, sulfur-based secondary batteries exhibit low intrinsic conductivity, low reactivity, and a significant shuttle effect, which greatly limits the capacity utilization of the positive electrode material during cycling, resulting in poor cycle performance.

[0044] Currently, cathode materials include sulfur materials and conductive porous carriers. Sulfur materials include sulfur and / or sulfur-containing compounds. In existing technologies, sulfur materials are mostly deposited through mesoporous or microporous conductive porous carriers. Mesoporous conductive porous carriers have a relatively large pore volume, which makes it easy for materials to shuttle through. Microporous conductive porous carriers have a very small pore volume, which leads to an insufficient loading of active materials in the sulfur material, which is detrimental to the overall energy density.

[0045] To address the aforementioned technical problems, the first aspect of this application provides a secondary battery designed to suppress shuttle reactions and improve the cycle performance of the secondary battery.

[0046] The secondary battery provided in this application includes a positive electrode sheet, which includes a positive electrode material. The positive electrode material includes a sulfur material and a conductive porous carrier. The sulfur material is adsorbed in the pores of the conductive porous carrier, and the pores of the conductive porous carrier are composed of micropores and mesopores.

[0047] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0048] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode material.

[0049] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0050] 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.).

[0051] In some embodiments, the secondary battery is a lithium-sulfur battery, and the positive electrode material can be any positive electrode material known in the art for lithium-sulfur batteries. As an example, the positive electrode material may include at least one of the following materials: elemental sulfur, sulfur-containing compounds, or mixtures thereof. Sulfur-containing compounds may, in particular, be Li₂S. n(n≥1), organic sulfur compounds or carbon-sulfur polymers (C2S) x (n, where x = 2.5 to 50, and n ≥ 2). Since sulfur materials used as cathode materials are not conductive when used alone, they can be blended with conductive porous carriers and used as cathode materials.

[0052] In some embodiments, the secondary battery is a sodium-sulfur battery, and the positive electrode material can be any positive electrode material known in the art for sodium-sulfur batteries. As an example, the positive electrode material may include at least one of the following materials: elemental sulfur, sulfur-containing compounds, or mixtures thereof. Sulfur-containing compounds may, in particular, be Na₂S. n (n≥1), organic sulfur compounds or carbon-sulfur polymers (C2S) x (n, where x = 2.5 to 50, and n ≥ 2). Since sulfur materials used as cathode materials are not conductive when used alone, they can be blended with conductive porous carriers and used as cathode materials.

[0053] The pores of conductive porous carriers mainly consist of two types: micropores and mesopores. Micropores refer to pores with a diameter less than 2 nm, while mesopores are pores with a diameter in the range of 2 nm to 50 nm. The conductive porous carrier of this application can be a single type of conductive porous carrier, whose pore structure can simultaneously include micropores and mesopores, i.e., the conductive porous carrier is a micro-mesoporous conductive carrier. Of course, the conductive porous carrier can also be two or more types of conductive porous carriers, as long as the pore structure of the conductive porous carrier simultaneously includes micropores and mesopores. For example, a mixture of microporous conductive carriers and mesoporous conductive carriers, or a mixture of micro-mesoporous conductive carriers and microporous conductive carriers, or a mixture of micro-mesoporous conductive carriers and mesoporous conductive carriers can be used.

[0054] As an example, the conductive porous carrier employs a micro-mesoporous conductive carrier. This carrier can physically and chemically confine sulfur materials. The physical confinement mainly includes spatial and diffusion restrictions. Spatial confinement is primarily manifested in the limited pore size of the micro-mesoporous conductive carrier. When the size of the sulfur material is too large, it cannot enter the pores of the micro-mesoporous conductive carrier and can only be adsorbed on the outer surface of the carrier, thus limiting the adsorption capacity. Diffusion restrictions are primarily manifested in the fact that although the existence of mesopores provides certain channels for material transport, the diffusion rate of some larger active molecules or ions in the mesopores may still be slow. Moreover, the space within the micropores is small, and the diffusion resistance of molecules in the micropores is greater. This restricts the diffusion of active materials inside the carrier, affecting the adsorption efficiency and uniformity.

[0055] Chemical limitations mainly include limitations imposed by surface chemistry and limitations imposed by chemisorption sites. Surface chemistry limitations are primarily manifested in the fact that the surface chemical properties of the microporous conductive support, such as surface functional groups and charge distribution, affect its adsorption of active materials. If the interaction between the functional groups on the support surface and the active material is weak, adsorption will be limited. Chemisorption site limitations are primarily manifested in the fact that the number of chemisorption sites on the microporous conductive support is finite. These sites are the key sites for chemisorption between the active material and the support. When the amount of active material exceeds the number of adsorption sites, the excess active material cannot be adsorbed, thus limiting the adsorption amount. Simultaneously, the activity of the adsorption sites also affects adsorption.

[0056] In this application, the pores of the conductive porous carrier are composed of a mixture of micropores and mesopores, rather than simply adjusting the pore size. This allows for physicochemical confinement of the sulfur material, greatly limiting the shuttle effect of the sulfur material during the charging and discharging process of the secondary battery, thereby improving the cycle performance of the secondary battery.

[0057] Meanwhile, since the pores of the conductive porous carrier are composed of a mixture of micropores and mesopores, a relatively high sulfur loading can be guaranteed.

[0058] The surface of the microporous conductive carrier has high chemical activity, which can adsorb sulfur materials through chemical bonding, enhance the binding force between sulfur materials and electrode materials, and reduce the dissolution and migration of sulfur materials in the electrolyte.

[0059] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0060] In some embodiments, the positive electrode film 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.

[0061] In some embodiments, the average pore size of the conductive porous carrier is 2nm-4nm (e.g., 2nm, 2.5nm, 3nm, 3.5nm, 4nm, and any range between two endpoints). This application limits the average pore size of the conductive porous carrier to a suitable range, which is beneficial for achieving physicochemical confinement of sulfur materials, suppressing the shuttle effect, and also ensuring a relatively high sulfur loading.

[0062] In some embodiments, the total pore volume of the conductive porous carrier is 0.1 cm³. 3 / g-1cm3 / g (e.g., 0.1cm) 3 / g, 0.2cm 3 / g, 0.5cm 3 / g, 0.8cm 3 / g, 1cm 3 / g and the interval between any two endpoints).

[0063] This application limits the total pore volume of the conductive porous support to a suitable range, which is beneficial for achieving physicochemical confinement of sulfur materials, suppressing the shuttle effect, and ensuring a relatively high sulfur material loading. By adjusting the pore volume of the conductive porous support, this application can control the sodium sulfide loading, thereby optimizing the electronic conductivity and ion diffusion of the electrode material and improving the electrochemical performance of the secondary battery.

[0064] In some embodiments, the conductive porous support includes a microporous carbon support. The conductive porous support of this application uses a microporous carbon support, which has a high specific surface area and porosity, beneficial for the loading and physical confinement of sulfur materials. Furthermore, the microporous carbon support exhibits good conductivity, enabling effective electron transfer during the charging and discharging process of the secondary battery, resulting in good electrochemical performance. Simultaneously, the microporous carbon support possesses high chemical stability, strong controllability, and strong adsorption capacity, which is beneficial for improving the sulfur loading capacity and cycle stability of the materials.

[0065] In some embodiments, the carbon support includes at least one of nitrogen-doped microporous carbon, nitrogen-doped microporous carbon derived from metal-organic frameworks, ordered microporous carbon, and microporous activated carbon.

[0066] Nitrogen-doped micro-mesoporous carbon possesses both microporous and mesoporous structures. Nitrogen-doped micro-mesoporous carbon derived from metal-organic frameworks (such as nitrogen-doped micro-mesoporous carbon derived from ZIF-8 (zeolite imidazole ester framework material)) has both microporous and mesoporous structures, with high specific surface area and porosity, which is beneficial for the adsorption of sulfur materials. Nitrogen doping can improve the conductivity of materials, which is beneficial for achieving high specific capacity and good cycle performance of secondary batteries.

[0067] Ordered micro-mesoporous carbon possesses a highly ordered pore structure with regular and uniform pore arrangement, which facilitates electrolyte penetration and ion transport, increasing the rate of electrode reactions and thus achieving high capacity. Simultaneously, the presence of micropores and mesopores in ordered micro-mesoporous carbon results in a high specific surface area, which is beneficial for the adsorption of sulfur materials.

[0068] Microporous activated carbon possesses both microporous and mesoporous structures, exhibiting high specific surface area and porosity, which is beneficial for the adsorption of sulfur materials. As an example, the microporous activated carbon can be at least one of YP50 activated carbon and YP51 activated carbon.

[0069] In some embodiments, the mass ratio of sulfur material to conductive porous carrier is 0.5:3-2.5:3 (e.g., 0.5:3, 1:3, 1.5:3, 2:3, 2.5:3, and any range between the two endpoints). This application selects an appropriate mass ratio of sulfur material to conductive porous carrier to better adsorb and disperse sulfur material, increasing the sulfur loading and thus improving cycle performance, while also increasing the theoretical specific capacity of the secondary battery. If the mass ratio is too small (i.e., the sulfur content is too low), the theoretical specific capacity of the secondary battery will decrease; if the mass ratio is too large (i.e., the sulfur content is too high), the sulfur material cannot be effectively adsorbed and dispersed, leading to a decrease in the utilization rate of sulfur material, thereby increasing the internal resistance of the secondary battery and deteriorating cycle performance.

[0070] In some embodiments, the sulfur material includes sodium sulfide, meaning the secondary battery is a sodium sulfide battery. Sodium sulfide batteries have the advantages of low cost and high theoretical energy density.

[0071] During the charging and discharging process of sodium sulfide batteries, sodium sulfide generates polysulfide intermediates. These polysulfides readily dissolve in the electrolyte and shuttle between the positive and negative electrodes, leading to capacity decay and poor cycle performance. The conductive porous carrier used in the positive electrode material of this application has pores composed of a mixture of micropores and mesopores, which can effectively suppress the aforementioned shuttle effect and improve the capacity and cycle performance of sodium sulfide batteries.

[0072] A second aspect of the present invention also provides a positive electrode material, the positive electrode material comprising a sulfur material and a conductive porous carrier, wherein the sulfur material is adsorbed within the pores of the conductive porous carrier, and the pores of the conductive porous carrier are composed of micropores and mesopores.

[0073] In some embodiments, the average pore size of the conductive porous carrier is 2nm-4nm.

[0074] In some embodiments, the total pore volume of the conductive porous carrier is 0.1 cm³. 3 / g-1cm 3 / g.

[0075] In some embodiments, the conductive porous support includes a microporous carbon support.

[0076] In some embodiments, the carbon support includes at least one of nitrogen-doped microporous carbon, nitrogen-doped microporous carbon derived from metal-organic frameworks, ordered microporous carbon, and microporous activated carbon.

[0077] In some embodiments, the mass ratio of sulfur material to the conductive porous carrier is 0.5:3-2.5:3.

[0078] In some embodiments, the method for preparing the cathode material of this application includes the following steps:

[0079] A mixture of sulfur material and conductive porous carrier is obtained, wherein the pores of the conductive porous carrier consist of micropores and mesopores.

[0080] The mixture is heated so that the sulfide melts and is adsorbed into the micropores and mesopores of the conductive porous carrier. After cooling, the positive electrode material is obtained.

[0081] Specifically, sulfur materials and conductive porous carriers are mixed according to a mass ratio and ball-milled for 5-7 hours (e.g., 5h, 6h, 7h, or any interval between the two endpoints) to ensure uniform dispersion. The mixture obtained from ball milling is then transferred to a high-temperature corundum crucible and annealed at high temperature under an argon atmosphere. The temperature program is as follows: Ventilate at 20℃ for 0.5h-3h (e.g., 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, or any interval between two endpoints), then raise the temperature to 950℃-1000℃ (e.g., 950℃, 960℃, 970℃, 980℃, 990℃, 1000℃, or any interval between two endpoints) at a rate of 5℃ / min-10℃ / min (e.g., 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or any interval between two endpoints), and hold at this temperature for 10h-12h (e.g., 10h, 11h, 1...). The temperature is increased to 1050℃-1100℃ (e.g., 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, 1100℃, and any two-endpoint range) at a rate of 5℃ / min-10℃ / min (e.g., 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, and any two-endpoint range) and held for 2h-4h (e.g., 2h, 3h, 4h, and any two-endpoint range) to ensure that the molten sodium sulfide fully enters the pores, and finally cooled to room temperature.

[0082] A third aspect of this application also provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive active material layer includes the positive electrode material provided in the second aspect.

[0083] 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 electrode 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.

[0084] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0085] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0086] 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.).

[0087] In some embodiments, the secondary battery is a lithium-sulfur battery, and the negative electrode material can be a negative electrode active material known in the art for lithium-sulfur batteries. As an example, the negative electrode active material may include at least one of the following materials: a material capable of reversibly inserting or deintercalating lithium ions (Li+), a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal, or a lithium alloy, etc. For example, a material capable of reversibly inserting or deintercalating lithium ions (Li+)... + The material can be crystalline carbon, amorphous carbon, or a mixture thereof. It can react with lithium ions (Li... + The material that reversibly forms a lithium-containing compound through the reaction can be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy can be, for example, an alloy of lithium (Li) and a metal selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), silicon (Si), and tin (Sn). However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0088] In some embodiments, the secondary battery is a sodium-sulfur battery, and the negative electrode material can be a negative electrode active material known in the art for lithium-sulfur batteries. As an example, the negative electrode active material may include at least one of the following materials: capable of reversibly inserting or de-intercalating sodium ions (Na₂O₃). + Materials that can react with sodium ions to reversibly form sodium-containing compounds, sodium metals, or sodium alloys, etc. For example, materials capable of reversibly inserting or deintercalating sodium ions (Na₂O₃). + The material can be crystalline carbon, amorphous carbon, or a mixture thereof. It can react with sodium ions (Na+). +The material that reversibly forms a sodium-containing compound in the reaction can be, for example, tin oxide, titanium nitrate, or silicon. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0089] In some embodiments, the negative electrode film layer may optionally include a binder. The binder 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).

[0090] In some embodiments, the negative electrode film 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.

[0091] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0092] 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.

[0093] 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.

[0094] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0095] In some embodiments, the secondary battery is a lithium-sulfur battery, and the electrolyte salt 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.

[0096] In some embodiments, the secondary battery is a sodium-sulfur battery, and the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorosulfonamide, sodium ditrifluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0097] In some embodiments, 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.

[0098] 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.

[0099] In some embodiments, the secondary battery further includes a separator, the materials of which include, but are not limited to, glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0100] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0101] 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.

[0102] 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.

[0103] 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 4 This is an example of a square-structured secondary battery 5.

[0104] In some implementations, refer to Figure 5The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator can be formed into an electrode assembly 52 through 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 lithium-sulfur 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.

[0105] A fourth aspect of this invention also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the 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.

[0106] 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 the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0107] Example 1

[0108] Preparation of the cathode material: Anhydrous sodium sulfide and porous carbon support were thoroughly mixed at a mass ratio of 2:3. The porous carbon support was nitrogen-doped micro / mesoporous carbon derived from ZIF-8. The mixture was then ball-milled for 6 hours. The ball-milled mixture was transferred to a high-temperature corundum crucible and annealed at high temperature under an argon atmosphere. The specific temperature program was as follows: 20℃ for 0.5 hours, heating to 950℃ at a rate of 10℃ / min, holding at 950℃ for 12 hours, then heating to 1050℃ at a rate of 5℃ / min, holding at 1050℃ for 2 hours to ensure that the molten sodium sulfide fully penetrated into the pores, and finally cooling to room temperature to obtain the cathode material.

[0109] Preparation of positive electrode sheet: The positive electrode material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed evenly in a weight ratio of 7:2:1. Then, a certain amount of N-methylpyrrolidone solvent is added, and a positive electrode slurry is obtained under the action of a vacuum stirrer. The positive electrode slurry is evenly coated on aluminum foil. After the aluminum foil is dried at room temperature, it is transferred to an 80℃ oven to dry for 12 hours. The foil is then cut into positive electrode sheets with a diameter of 14 mm using a cutting machine.

[0110] Preparation of negative electrode sheet: Hard carbon material, conductive agent carbon black, binder styrene-butadiene rubber, and carboxymethyl cellulose are mixed evenly in an appropriate amount of deionized water at a mass ratio of 96:1.5:1.5:1 to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of the copper foil of the negative electrode current collector. By drying and cold pressing, a negative electrode active material layer is formed on both sides of the negative electrode current collector. Finally, the negative electrode sheet is obtained by slitting and cutting.

[0111] Preparation of electrolyte: In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvent sodium difluorosulfonamide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0112] Separator: Glass fiber membrane is used as the separator.

[0113] Assembly of sodium sulfide batteries: In the glove box, place the positive electrode, separator, and negative electrode into the button cell in sequence; add an appropriate amount of electrolyte to fully wet the positive electrode, negative electrode, and separator; seal the battery case to ensure good battery sealing.

[0114] Example 2

[0115] The difference between Example 2 and Example 1 is that the porous carbon support in the cathode material is an ordered micro-mesoporous carbon, while all other operations are the same as in Example 1.

[0116] Example 3

[0117] The difference between Example 3 and Example 1 is that the porous carbon support in the cathode material is YP50 activated carbon, while all other operations are the same as in Example 1.

[0118] Example 4

[0119] The difference between Example 4 and Example 1 is that the porous carbon support in the cathode material is YP51 activated carbon, while all other operations are the same as in Example 1.

[0120] Example 5

[0121] The difference between Example 5 and Example 1 is that the mass ratio of anhydrous sodium sulfide to porous carbon support in the cathode material is 0.5:3, while all other operations are the same as in Example 1.

[0122] Example 6

[0123] The difference between Example 6 and Example 1 is that the mass ratio of anhydrous sodium sulfide to porous carbon support in the cathode material is 1:3, while all other operations are the same as in Example 1.

[0124] Example 7

[0125] The difference between Example 7 and Example 1 is that the mass ratio of anhydrous sodium sulfide to porous carbon support in the cathode material is 2.5:3, while all other operations are the same as in Example 1.

[0126] Comparative Example 1

[0127] The difference between Comparative Example 1 and Example 1 is that the porous carbon support in the cathode material is a KB mesoporous and macroporous mixed carbon (referring to a mixed system of Ketjen Black (KB) and carbon materials with mesoporous and macroporous structures), while all other operations are the same as in Example 1.

[0128] Comparative Example 2

[0129] The difference between Comparative Example 2 and Example 1 is that the porous carbon support in the cathode material is CMK mesoporous carbon, while all other operations are the same as in Example 1.

[0130] BET testing of porous carbon supports: BET tests were performed on the porous carbon supports in Examples 1-4 and Comparative Examples 1-2 to obtain pore structure data. The test results are shown in Table 1. The nitrogen adsorption-desorption curves of the nitrogen-doped micro / mesoporous carbon derived from ZIF-8 are shown in Table 1. Figure 1 As shown, the nitrogen adsorption-desorption curves of ordered micro-mesoporous carbon are as follows: Figure 2 As shown.

[0131] Table 1 shows the pore structure data of the porous carbon supports in Examples 1-4 and Comparative Examples 1-2.

[0132]

[0133]

[0134] From Table 1 and Figure 1-2 It can be seen that the nitrogen-doped microporous carbon derived from ZIF-8 (ZIF-8-CN), YM (ordered microporous carbon), YP50 activated carbon and YP51 activated carbon are microporous mixed structures; CMK mesoporous carbon is a mesoporous structure as a whole, and KB carbon is a mixed structure of mesoporous and macroporous structures.

[0135] Furthermore, the scanning electron microscope image of the nitrogen-doped microporous carbon derived from ZIF-8 in Example 1 is shown below. Figure 3 As shown, from Figure 3 The dodecahedral morphology and porous surface of nitrogen-doped microporous carbon derived from ZIF-8 can be seen.

[0136] Capacity testing of sodium sulfide batteries: Electrochemical performance tests were conducted on the sodium sulfide batteries of each embodiment and comparative example using the Blue Battery testing system. The battery testing temperature was kept constant at approximately 25°C, and the voltage range was 0.5-2.5V. The constant current charge / discharge current density and specific capacity were calculated based on the active mass of sodium sulfide in the positive electrode. The specific test current was as follows: initial activation was performed at a current density of 0.05C, followed by 10 cycles at 0.05C, and then 100 cycles at a current density of 0.33C. The test results are shown in Table 2.

[0137] The capacity retention rate is calculated as follows: Taking Example 1 as an example, the battery capacity retention rate is calculated as follows: At 25°C, the sodium sulfide battery corresponding to Example 1 is left to stand for 4 hours, then charged to 2.5V at a constant current of 0.05C, and then discharged to 0.5V at a constant current of 0.05C. The resulting capacity is recorded as the initial capacity C0. After resting for 2 minutes, it is cycled 10 times at a current density of 0.05C, and the resulting capacity is C10. Then it is cycled 100 times at a current density of 0.33C. The charge / discharge capacity of the first cycle at 0.33C is recorded as C11, and the charge / discharge capacity of the last cycle is recorded as C110. The battery capacity retention rate under 0.05C is P10 = C10 / C0 × 100%, and the capacity retention rate under 0.33C is P110 = C110 / C11 × 100%.

[0138] Table 2. Capacity test results of sodium sulfide batteries in each embodiment and comparative example.

[0139]

[0140]

[0141] As can be seen from the data in Table 2, compared to Comparative Example 1 which used a mixture of mesoporous and macroporous carbon and Comparative Example 2 which used mesoporous carbon, Examples 1-7 of this application use microporous carbon as the conductive carrier of the positive electrode material of the sodium sulfide battery, which can improve the capacity and cycle performance of the sodium sulfide battery. Furthermore, by reasonably adjusting the type of microporous carbon carrier and the mass ratio of sodium sulfide to mesoporous carbon carrier, a sodium sulfide battery with higher capacity and better cycle performance can be obtained. Specifically, the smaller the mass ratio of sodium sulfide to microporous carbon carrier (i.e., the more microporous carbon carrier used), the higher the capacity and capacity retention rate of the sodium sulfide battery.

[0142] 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, characterized in that, The device includes a positive electrode sheet, which includes a positive electrode material. The positive electrode material includes a sulfur material and a conductive porous carrier. The sulfur material is adsorbed within the pores of the conductive porous carrier, and the pores of the conductive porous carrier are composed of micropores and mesopores.

2. The secondary battery as described in claim 1, characterized in that, The average pore size of the conductive porous carrier is 2nm-4nm.

3. The secondary battery as described in claim 1, characterized in that, The total pore volume of the conductive porous carrier is 0.1 cm³. 3 / g-1cm 3 / g.

4. The secondary battery as described in claim 1, characterized in that, The conductive porous support includes a microporous carbon support.

5. The secondary battery as described in claim 4, characterized in that, The microporous carbon support includes at least one of nitrogen-doped microporous carbon, nitrogen-doped microporous carbon derived from metal-organic frameworks, ordered microporous carbon, and microporous activated carbon.

6. The secondary battery as described in claim 1, characterized in that, The mass ratio of the sulfur material to the conductive porous carrier is 0.5:3 to 2.5:

3.

7. The secondary battery as described in any one of claims 1 to 6, characterized in that, The sulfur material includes sodium sulfide.

8. A positive electrode material, characterized in that, It includes a sulfur material and a conductive porous carrier, wherein the sulfur material is adsorbed within the pores of the conductive porous carrier, and the pores of the conductive porous carrier are composed of micropores and mesopores.

9. The cathode material as described in claim 8, characterized in that, The average pore size of the conductive porous carrier is 2nm-4nm.

10. The cathode material as described in claim 8, characterized in that, The total pore volume of the conductive porous carrier is 0.1 cm³. 3 / g-1cm 3 / g.

11. The cathode material as described in claim 8, characterized in that, The conductive porous support includes a microporous carbon support.

12. The cathode material as described in claim 11, characterized in that, The microporous carbon support includes at least one of nitrogen-doped microporous carbon, nitrogen-doped microporous carbon derived from metal-organic frameworks, ordered microporous carbon, and microporous activated carbon.

13. The cathode material according to any one of claims 8 to 12, characterized in that, The mass ratio of the sulfur material to the conductive porous carrier is 0.5:3 to 2.5:

3.

14. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer including the positive electrode material as described in any one of claims 8 to 13.

15. An electrical appliance, characterized in that, The electrical device includes a secondary battery as described in any one of claims 1 to 7.

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