Positive electrode active material and preparation method therefor, battery cell, battery device, and electrical device

Abstract

The present application discloses a positive electrode active material and a preparation method therefor, a battery cell, a battery device, and an electrical device. The battery cell comprises a positive electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector. The positive electrode film layer comprises a positive electrode active material. The positive electrode active material comprises a sulfide positive electrode material. The sulfide positive electrode material comprises: an inner core, comprising porous carbon and an alkali metal sulfide, the alkali metal sulfide being filled in pores of the porous carbon; and a carbon coating material, coating at least part of the surface of the inner core, wherein the oxygen content of the sulfide positive electrode material is less than or equal to 0.05%. The battery cell provided by the present application has improved cycle performance.

Description

Positive electrode active materials and their preparation methods, battery cells, battery devices, and electrical devices.

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411925613.6, filed on December 25, 2024, entitled “Positive Electrode Active Material and Preparation Method Thereof, Battery Cell, Battery Device, and Power Consumable Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, specifically to a positive electrode active material and its preparation method, a battery cell, a battery device, and an electrical device. Background Technology

[0004] Batteries are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric car toys, electric toy ships, electric toy airplanes, and power tools.

[0005] In the development of battery cells, improving the cycle performance of battery cells is one of the urgent problems to be solved. Summary of the Invention

[0006] To address the aforementioned technical problems, this application provides a positive electrode active material and its preparation method, a battery cell, a battery device, and an electrical device.

[0007] In a first aspect, embodiments of this application provide a battery cell, comprising: a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including a sulfide positive electrode material, the sulfide positive electrode material including: a core comprising porous carbon and alkali metal sulfides filling the pores of the porous carbon; and a carbon coating material coating at least a portion of the surface of the core; wherein the oxygen content of the sulfide positive electrode material is less than or equal to 0.05%.

[0008] According to embodiments of this application, by filling the pores of porous carbon with alkali metal sulfides, the carbon coating material covering at least a portion of the core surface can suppress the dissolution of alkali metal sulfides in the pores, confining the alkali metal sulfides within the pores of the porous carbon. This restricts the reaction of alkali metal sulfides during the charge and discharge process of the battery cell to the pores of the porous carbon, thereby reducing the shuttle effect of polysulfides generated at the positive electrode, reducing the consumption of active materials, and enabling the battery cell to achieve higher energy efficiency. Furthermore, the framework structure of porous carbon can suppress the volume expansion and contraction of alkali metal sulfides during charge and discharge, thereby reducing the volume change of the positive electrode sheet, giving the positive electrode sheet higher structural stability, and improving the cycle performance of the battery cell. Additionally, by reducing the content of oxygen-containing active groups on the surface of porous carbon, the oxygen content of the sulfide positive electrode material is kept within a low range, which can reduce the consumption of active materials during the charge and discharge cycle of the battery cell, reduce irreversible capacity loss of the battery cell, and thus improve the cycle performance of the battery cell.

[0009] In some embodiments, the theoretical sulfur loading of the porous carbon is M0, the mass content of sulfur in the core is M1, and 0.2≤M1 / M0≤0.95.

[0010] In some embodiments, 0.3 ≤ M1 / M0 ≤ 0.8.

[0011] In some embodiments, 50% ≤ M0 ≤ 90%.

[0012] In some embodiments, the most probable pore size of the porous carbon is 1 nm to 5 nm.

[0013] In some embodiments, the porous carbon has a pore volume of 0.3 cm³. 3 / g-4cm 3 / g.

[0014] In some embodiments, the specific surface area of ​​the porous carbon is 400 m². 2 / g-1500m 2 / g.

[0015] In some embodiments, the porous carbon includes one or more of mesoporous carbon and microporous carbon.

[0016] In some embodiments, the alkali metal sulfide includes one or both of lithium sulfide and sodium sulfide.

[0017] In some embodiments, the carbon coating material forms a carbon coating layer on at least a portion of the surface of the core, the thickness of the carbon coating layer being 3 nm to 100 nm.

[0018] Secondly, embodiments of this application provide a battery device, including a single battery cell from the first aspect of this application.

[0019] Thirdly, embodiments of this application provide an electrical device, including a battery cell from the first aspect of this application or a battery device from the second aspect of this application.

[0020] Fourthly, embodiments of this application provide a positive electrode active material, including a sulfide positive electrode material, wherein the sulfide positive electrode material comprises: a core, including porous carbon and alkali metal sulfides filling the pores of the porous carbon; and a carbon coating material, coating at least a portion of the surface of the core; wherein the oxygen content of the sulfide positive electrode material is less than or equal to 0.05%.

[0021] Fifthly, embodiments of this application provide a method for preparing a positive electrode active material, comprising the following steps:

[0022] Porous carbon is mixed with elemental sulfur and heated to melt and fill the pores of the porous carbon, thus obtaining a sulfur-carbon composite.

[0023] A pre-reactant containing an alkali metal organic salt is provided. The sulfur-carbon complex is mixed with the pre-reactant and reacted with elemental sulfur in the pores of the porous carbon to generate alkali metal sulfides in situ, thereby obtaining an alkali metal sulfide-carbon complex.

[0024] A carbon source is provided such that the carbon source forms a carbon coating layer on at least a portion of the surface of the alkali metal sulfide-carbon complex.

[0025] According to embodiments of this application, elemental sulfur is filled into the pores of porous carbon by heating and melting. Then, the elemental sulfur reacts in situ with a pre-reactant within the pores of the porous carbon to generate alkali metal sulfides, thereby filling the pores of the porous carbon with these alkali metal sulfides. Since the pre-reactant needs to react with elemental sulfur to generate sulfides, it possesses high reducing power. When this highly reducing pre-reactant is mixed with porous carbon, it can reduce the oxygen-containing active groups on the surface of the porous carbon to form a film. This film is mainly composed of organic salts and can be removed by solvent reaction or high-temperature removal. This significantly reduces the content of oxygen-containing active groups on the surface of the porous carbon, reducing the reaction consumption of active metals by oxidized groups, thereby improving the capacity utilization of the battery cell. Therefore, the preparation method provided in this application embodiment can be used to prepare the positive electrode active material provided in this application embodiment.

[0026] In some embodiments, in the step of heating the porous carbon with elemental sulfur, the heating temperature is 100°C-200°C.

[0027] In some embodiments, the step of providing a pre-reactant containing an alkali metal organosalt includes: reacting an aromatic compound with an alkali metal in a solvent to obtain the pre-reactant.

[0028] In some embodiments, the molar concentration of the alkali metal organic salt in the pre-reactant is 0.5 mol / L to 3 mol / L.

[0029] In some embodiments, the alkali metal includes one or both of lithium and sodium.

[0030] In some embodiments, the solvent includes one or more of ethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0031] In some embodiments, the molar ratio of the aromatic compound to the alkali metal is 1:(1-1.1).

[0032] In some embodiments, the molar ratio of the elemental sulfur to the alkali metal organosalt is 1:(2-2.5).

[0033] In some embodiments, the step of mixing the sulfur-carbon complex with the pre-reactant and reacting it with elemental sulfur in the pores of the porous carbon to generate alkali metal sulfides in situ satisfies the following condition: the reaction temperature of the sulfur-carbon complex with the pre-reactant is 25°C-100°C.

[0034] In some embodiments, the reaction time between the sulfur-carbon complex and the pre-reactant is 2h-48h.

[0035] In some embodiments, the step of forming a carbon coating layer on at least a portion of the surface of the alkali metal sulfide-carbon complex using the carbon source includes: forming a carbon coating layer on at least a portion of the surface of the alkali metal sulfide-carbon complex using chemical vapor deposition.

[0036] In some embodiments, the carbon source includes one or more of gaseous hydrocarbons and liquid organic compounds. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described 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 drawings without creative effort.

[0038] Figure 1 is a schematic diagram of the structure of a vehicle provided in some embodiments of this application.

[0039] Figure 2 is a schematic diagram of the explosion of a battery provided in some embodiments of this application.

[0040] Figure 3 is an exploded view of the battery module shown in Figure 2.

[0041] Figure 4 shows the XRD patterns of the sulfide cathode materials in Example 1 and Comparative Example 1 of this application.

[0042] Figure 5 shows a SEM+EDS image of the sulfide cathode material in Example 1 of this application.

[0043] Figure 6 shows the SEM+EDS image of the sulfide cathode material in Comparative Example 1 of this application.

[0044] The accompanying drawings are not necessarily drawn to scale.

[0045] The reference numerals in the attached drawings are explained as follows: 1. Vehicle; 2. Battery unit; 3. Controller; 4. Motor; 5. Housing; 5a. First housing section; 5b. Second housing section; 5c. Reception space; 6. Battery module; 7. Battery cell. Detailed Implementation

[0046] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its preparation method, battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0047] 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.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0049] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0050] 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.

[0051] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0052] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0053] In the description of the embodiments of this application, unless otherwise specified, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0054] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0055] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0056] The battery device mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0057] A single battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. When there are multiple battery cells, they are connected in series, parallel, or mixed connections through a busbar.

[0058] In some embodiments, the battery device may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module.

[0059] In some embodiments, the battery device may be a battery pack, which includes a housing and individual battery cells, with the individual battery cells or battery modules housed within the housing.

[0060] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0061] In some embodiments, the battery device may be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0062] The technical solutions described in the embodiments of this application are applicable to battery devices and electrical devices that use battery devices.

[0063] Battery devices can be used as the power source for electrical devices or as energy storage units for electrical devices. Electrical devices can be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), vehicles (such as 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.

[0064] Electrical devices can choose the type of battery device according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0065] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device.

[0066] Figure 1 is a schematic diagram of the structure of a vehicle provided in some embodiments of this application.

[0067] As shown in Figure 1, a battery device 2 is installed inside the vehicle 1. The battery device 2 can be located at the bottom, front, or rear of the vehicle 1. The battery device 2 can be used to power the vehicle 1; for example, the battery device 2 can serve as the operating power source for the vehicle 1.

[0068] The vehicle 1 may also include a controller 3 and a motor 4. The controller 3 is used to control the battery device 2 to supply power to the motor 4, for example, for the power needs of the vehicle 1 during starting, navigation and driving.

[0069] In some embodiments, the battery device 2 can not only serve as the operating power source for the vehicle 1, but also as the driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0070] Figure 2 is an exploded view of a battery provided in some embodiments of this application. As shown in Figure 2, the battery device 2 includes a housing 5 and a battery cell (not shown), with the battery cell housed within the housing 5.

[0071] The housing 5 is used to house individual battery cells, and the housing 5 can have various structures. In some embodiments, the housing 5 may include a first housing portion 5a and a second housing portion 5b, which overlap each other, and together define a housing space 5c for housing the individual battery cells. The second housing portion 5b may be a hollow structure with one end open, and the first housing portion 5a may be a plate-like structure, with the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c; alternatively, both the first housing portion 5a and the second housing portion 5b may be hollow structures with one side open, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c. Of course, the first housing portion 5a and the second housing portion 5b can have various shapes, such as cylinders, cuboids, etc.

[0072] To improve the sealing performance after the first housing part 5a and the second housing part 5b are connected, a sealing element, such as sealant or sealing ring, can also be provided between the first housing part 5a and the second housing part 5b.

[0073] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0074] In battery device 2, there can be one or more battery cells. If there are multiple battery cells, they can be connected in series, in parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells are connected in both series and parallel configurations. Multiple battery cells can be directly connected in series, in parallel, or in a mixed configuration, and then the whole assembly of multiple battery cells is housed in housing 5. Alternatively, multiple battery cells can first be connected in series, in parallel, or in a mixed configuration to form battery module 6, and then multiple battery modules 6 can be connected in series, in parallel, or in a mixed configuration to form a whole assembly, which is then housed in housing 5.

[0075] Figure 3 is an exploded view of the battery module shown in Figure 2.

[0076] As shown in Figure 3, in some embodiments, there are multiple battery cells 7, which are first connected in series, parallel, or mixed to form a battery module 6. The multiple battery modules 6 are then connected in series, parallel, or mixed to form a whole and housed in a casing.

[0077] Multiple battery cells 7 in battery module 6 can be electrically connected through a busbar component to achieve parallel, series, or mixed connection of multiple battery cells 7 in battery module 6.

[0078] The battery cell provided in this application embodiment is a negative electrode-free battery cell, which may include at least one of a negative electrode-free lithium metal battery cell and a negative electrode-free sodium metal battery cell.

[0079] A negative electrode-free battery cell typically refers to a battery cell in which no negative electrode active material layer is actively formed on the negative electrode side during the battery cell manufacturing process. For example, the negative electrode active material layer is not formed at the negative electrode through coating or deposition processes, or it is formed from a carbonaceous active material layer. During the first charge, ions gain electrons on the negative electrode side and deposit metal on the surface of the negative electrode current collector. During discharge, the metal can be converted back into ions and return to the positive electrode, achieving cyclic charging and discharging. Compared to other battery cells, a negative electrode-free battery cell can achieve a higher energy density due to the absence of a negative electrode active material layer. In some embodiments, to improve battery cell performance, some conventional materials that can be used as negative electrode active materials, such as carbon materials, can also be placed on the negative electrode side of the negative electrode-free battery cell. Although these materials have a certain capacity, because their content is small and they are not used as the main negative electrode active material in the battery cell, such a battery cell can still be considered a negative electrode-free battery cell. The Cell Balance (CB) value of a negative electrode-free battery cell is typically very small; for example, in some embodiments, the CB value of a negative electrode-free battery cell can be less than or equal to 0.1. The CB value is the capacity per unit area of ​​the negative electrode divided by the capacity per unit area of ​​the positive electrode in the battery cell. Because a negative electrode-free battery cell contains little or no negative electrode active material, the capacity per unit area of ​​the negative electrode is small, and therefore the CB value is very small, typically less than or equal to 0.1.

[0080] The battery cell includes an electrode assembly. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited to this.

[0081] Electrode assemblies generally include a positive electrode, a negative electrode, and a separator.

[0082] Lithium / sodium-sulfur battery cells use sulfur as the positive electrode, while electrodeless lithium / sodium-sulfur battery cells use lithium sulfide / sodium sulfide as the positive electrode. Since the positive electrode itself contains lithium / sodium, the use of highly active lithium or sodium metals directly at the negative electrode can be avoided during battery cell assembly, further reducing manufacturing costs. However, lithium sulfide and sodium sulfide are intrinsically near-electronic insulators with poor conductivity, resulting in poor redox kinetics during charge and discharge, leading to significant battery polarization and a capacity utilization far below the theoretical capacity. Furthermore, the shuttle effect during charge and discharge of lithium / sodium-sulfur battery cells—where polysulfide intermediates generated at the positive electrode dissolve into the electrolyte and diffuse through the separator to the negative electrode, reacting directly there—leads to the loss of effective active materials in the battery cell, resulting in battery cell lifespan degradation and low coulombic efficiency. A common strategy employed in related technologies to address the aforementioned technical problems is to utilize nanostructured carbon materials with high specific surface area. This reduces the shuttle effect of sulfides through physical confinement, while simultaneously providing electrical conductivity through nano-carbon. Although this method improves conductivity to some extent, its effect on reducing the consumption of effective active materials in battery cells is limited, resulting in still relatively poor capacity utilization of the battery cells.

[0083] In view of this, embodiments of this application provide a battery cell that, by adjusting the design of the lithium / sodium-sulfur battery cell, can reduce the consumption of effective active material in the positive electrode and enable the battery cell to achieve higher capacity utilization.

[0084] [Positive electrode plate]

[0085] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, the positive electrode film layer including a positive active material.

[0086] 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.

[0087] In some embodiments, the positive electrode active material includes a sulfide positive electrode material, which includes a core and a carbon coating material. The core includes porous carbon and alkali metal sulfides filling the pores of the porous carbon. The carbon coating material coats at least a portion of the surface of the core. The oxygen content of the sulfide positive electrode material is less than or equal to 0.05%.

[0088] In this embodiment, porous carbon is used as the matrix. Porous carbon has high electrical conductivity, which can effectively improve the conductivity of the sulfide cathode material. Alkali metal sulfides are filled into the channels of porous carbon, and the carbon coating material covering at least part of the core surface can inhibit the dissolution of alkali metal sulfides in the channels, thereby confining the alkali metal sulfides within the channels of porous carbon. This restricts the electrochemical reaction of alkali metal sulfides during the charge and discharge of the battery cell to the channels of porous carbon, thereby reducing the shuttle effect of polysulfides generated at the cathode, reducing the consumption of active materials, and enabling the battery cell to have higher energy utilization. In addition, the framework structure of porous carbon can suppress the volume expansion and contraction of alkali metal sulfides during charge and discharge, thereby reducing the volume change of the cathode sheet, giving the cathode sheet higher structural stability, which is beneficial to improving the cycle performance of the battery cell.

[0089] According to embodiments of this application, the oxygen in the sulfide cathode material mainly originates from oxygen-containing active groups (such as hydroxyl, carboxyl, and ether groups) on the porous carbon surface. These oxygen-containing active groups react with the active metals (Li, Na) generated during the charge-discharge cycle of the battery cell, consuming the active material, increasing the irreversible capacity loss of the battery cell, and affecting the capacity utilization and cycle life of the battery cell. In embodiments of this application, by reducing the content of oxygen-containing active groups on the porous carbon surface to control the oxygen content of the sulfide cathode material to a low range, the reaction between the active metal and the oxygen-containing active groups during the charge-discharge cycle of the battery cell can be reduced, thereby reducing the consumption of active material, reducing the irreversible capacity loss of the battery cell, and thus improving the cycle performance of the battery cell.

[0090] In this application, the oxygen content of the sulfide cathode material is a well-known concept in the art, and it can be obtained by known methods and instruments. For example, it can be tested using an organic elemental analyzer according to the standard testing method of organic elemental analysis (EA).

[0091] It should be noted that the oxygen content test sample for sulfide cathode materials can be taken directly from the sulfide cathode material or from a single battery cell. During testing, the sulfide cathode material can be cleaned in tetrahydrofuran solvent, then rinsed with deionized water, dried, and then tested.

[0092] In some embodiments, the theoretical sulfur loading of the porous carbon is M0, and the mass content of sulfur in the core is M1. M1 can satisfy: 0.2≤M1 / M0≤0.95. For example, M1 / M0 can be 0.2, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, or any range of the above values; optionally, 0.3≤M1 / M0≤0.8.

[0093] In this application, the theoretical sulfur loading of porous carbon refers to the maximum amount of sulfur that can be theoretically filled into the pores of porous carbon, which can be calculated from the pore volume of porous carbon. The theoretical sulfur loading of porous carbon M0(%) = m / (m+1)×100%, where m is the mass of elemental sulfur that can be contained in the pores of a unit mass of porous carbon. m can be calculated from the pore volume of porous carbon and the density of elemental sulfur. For example, if the pore volume of porous carbon is denoted as V and the density of elemental sulfur is ρ, then m = V×ρ.

[0094] According to the embodiments of this application, when calculating the theoretical sulfur loading of porous carbon, the pore volume includes the macropores and interstitials in the porous carbon. This results in the actual measured pore volume being larger than the total volume of the porous carbon channels. In addition, the alkali metal sulfides filling the channels of porous carbon contain not only sulfur but also alkali metal elements. Therefore, by making the actual sulfur content in the core lower than the theoretical sulfur loading of porous carbon and limiting its ratio within the above range, the alkali metal sulfides can be filled as completely as possible into the channels of porous carbon, reducing the distribution of alkali metal sulfides on the surface of porous carbon. This can further reduce sulfur dissolution during the charge and discharge cycle of the battery cell, improving the capacity utilization and cycle performance of the battery cell.

[0095] In this application, since sulfur in the sulfide cathode material is mainly distributed in the core, the mass content of sulfur in the core can be considered as the sulfur content in the sulfide cathode material. This content can be detected using equipment and methods known in the art, such as thermogravimetric analysis according to JYT014-1996. Specifically, based on the mass loss of the sample during heating, a mass-temperature curve (TG curve) is plotted. The mass loss corresponding to the decomposition temperature of the alkali metal sulfide is then read as the total mass of the alkali metal sulfide, and the mass content of sulfur is calculated accordingly.

[0096] In some embodiments, the theoretical sulfur loading of porous carbon, M0, can be 50% ≤ M0 ≤ 90%, for example, M0 can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any range of the above values; optionally, 60% ≤ M0 ≤ 85%.

[0097] According to the embodiments of this application, the theoretical sulfur loading of porous carbon is within the above range. It has a rich pore structure, which can accommodate more alkali metal sulfides while maintaining high strength and conductivity, which is beneficial to improving the capacity of battery cells.

[0098] In some embodiments, the pore volume of porous carbon can be 0.3 cm³. 3 / g-4cm 3 / g, for example, can be 0.3cm3 / g, 0.5cm 3 / g, 0.8cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.5cm 3 / g, 1.8cm 3 / g, 2.0cm 3 / g, 2.2cm 3 / g, 2.5cm 3 / g, 2.8cm 3 / g, 3.0cm 3 / g, 3.2cm 3 / g, 3.5cm 3 / g, 3.8cm 3 / g, 4.0cm 3 / g, or any range of the above values; optionally, the pore volume of the porous carbon can be 1.0 cm³. 3 / g-3.6cm 3 / g.

[0099] In this application, the pore volume of porous carbon refers to the total volume of pores in a unit mass of porous carbon, which can be measured using instruments and methods known in the art. For example, it can be determined using a pore size analyzer according to the nitrogen adsorption method.

[0100] In some embodiments, the most probable pore size of porous carbon can be 1 nm to 5 nm, for example, it can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or any range of the above values.

[0101] In this application, the most probable pore size of porous carbon has a meaning known in the art, which refers to the pore size in porous carbon with the largest rate of change of pore volume with pore size, and can be detected by instruments and methods known in the art, for example, it can be determined by using a pore size analyzer according to the nitrogen adsorption method.

[0102] When the most probable pore size of porous carbon is within the aforementioned range, it allows for better containment of alkali metal sulfides while reducing their dissolution in the electrolyte. With a smaller most probable pore size, alkali metal sulfides are less likely to completely fill the pores of the porous carbon, resulting in a lower amount of alkali metal sulfides loaded on the porous carbon and a lower positive electrode capacity. Conversely, with a larger most probable pore size, the sulfur fixation effect of the porous carbon is poor, increasing the risk of alkali metal sulfides dissolving from the pores during battery cell charge-discharge cycles. This leads to intensified side reactions, greater consumption of active materials, and accelerated cycle degradation of the battery cell, ultimately affecting its cycle life.

[0103] In some embodiments, the specific surface area of ​​porous carbon can be 400 m². 2 / g-1500m 2 / g, for example, can be 400m 2 / g、420m 2 / g、430m 2 / g、450m 2 / g、480m 2 / g、500m 2 / g、550m 2 / g、600m 2 / g、650m 2 / g、700m 2 / g、750m 2 / g、800m 2 / g、850m 2 / g、900m 2 / g、950m 2 / g, 1000m 2 / g, 1050m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g, 1400m 2 / g, 1500m 2 / g, or any range of the above values. Optionally, the specific surface area of ​​porous carbon can be 600 m². 2 / g-1200m 2 / g.

[0104] The specific surface area of ​​porous carbon is a well-known concept in the art and can be measured using known instruments and methods. For example, it can be measured according to the methods and instruments specified in GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method".

[0105] The specific surface area of ​​porous carbon is limited to the above range, and the sulfide cathode material can have a suitable contact area with the electrolyte, which is conducive to the electrochemical reaction and improves the electrochemical performance of the battery cell.

[0106] In some embodiments, porous carbon may include one or more of mesoporous carbon and microporous carbon. For example, it may include one or more of Ketjenblack (KB), activated carbon (YP), and zeolite imidazole ester framework material (ZIF-8), which can be sintered to form a carbon material with a porous structure.

[0107] In some embodiments, the carbon coating material forms a uniform carbon coating layer on at least a portion of the surface of the core. The thickness of the carbon coating layer can be 3nm-100nm, for example, it can be 3nm, 5nm, 8nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, or any combination of the above values, and can be selected as 10nm-85nm.

[0108] In this application, the morphology of the positive electrode active material can be obtained by scanning electron microscopy (SEM). The detection methods for parameters such as the distribution and content of each element in the positive electrode active material can include, but are not limited to, one or more of X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), inductively coupled plasma (ICP), and thermogravimetric analysis (TG).

[0109] Another embodiment of this application provides a method for preparing a positive electrode active material, including the following steps S10-S30:

[0110] S10, porous carbon is mixed with elemental sulfur and heated to melt and fill the pores of the porous carbon to obtain a sulfur-carbon composite.

[0111] S20 provides a pre-reactant containing an alkali metal organosalt. The sulfur-carbon complex is mixed with the pre-reactant and reacted with elemental sulfur in the pores of porous carbon to generate alkali metal sulfides in situ, thus obtaining an alkali metal sulfide-carbon complex.

[0112] S30 provides a carbon source, enabling the carbon source to form a carbon coating layer on at least a portion of the surface of the alkali metal sulfide-carbon complex.

[0113] The method for preparing sulfide cathode material provided in this application embodiment first fills the pores of porous carbon with elemental sulfur by heating and melting, and then allows elemental sulfur to react with a pre-reactant in situ in the pores of porous carbon to generate alkali metal sulfides, thereby allowing alkali metal sulfides to fill the pores of porous carbon.

[0114] Not limited to any theory or explanation, because the pre-reactant needs to react with elemental sulfur to form sulfides, it possesses high reducing power. When this highly reducing pre-reactant is mixed with porous carbon, it can reduce the oxygen-containing active groups on the surface of the porous carbon to form a film. This film is mainly composed of organic salts and can be removed by solvent reaction or high temperature. This significantly reduces the content of oxygen-containing active groups on the surface of the porous carbon, thereby reducing the reaction consumption of active metals by oxide groups and improving the capacity of the battery cell. According to the embodiments of this application, the preparation method provided in this application can be used to prepare the positive electrode active material provided in this application.

[0115] In some embodiments, in step S10, the temperature at which the sulfur element and porous carbon are mixed and heated can be 100℃-200℃, for example, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, or any range of the above values, and can be selected as 120℃-180℃.

[0116] According to the embodiments of this application, heating temperatures within the above-mentioned range can bring elemental sulfur to a molten state to fill the pores of porous carbon.

[0117] In some implementations, step S20, which involves providing a pre-reactant containing an alkali metal organosalt, may include reacting an aromatic compound with an alkali metal in a solvent to obtain the pre-reactant.

[0118] According to embodiments of this application, aromatic compounds and alkali metals can react in a solvent to obtain a pre-reactant containing an alkali metal organosalt, which can react with elemental sulfur to generate alkali metal sulfides.

[0119] In some embodiments, the alkali metal may include one or both of lithium metal and sodium metal.

[0120] In some embodiments, the aromatic compound may include one or more of biphenyl, terphenyl, naphthalene, anthracene, phenanthrene, pyrene, perylene, and their respective derivatives.

[0121] In some embodiments, the solvent may be an ether solvent, such as one or more of ethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0122] In some embodiments, the concentration of the alkali metal organosalt in the pre-reactant can be 0.5 mol / L to 3 mol / L, for example, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, or any range of the above values; optionally, the concentration of the alkali metal organosalt can be 0.8 mol / L to 2.6 mol / L.

[0123] According to the embodiments of this application, by controlling the concentration of alkali metal organic salt in the pre-reactant within the above-mentioned range, it can be made to fully react with elemental sulfur to generate alkali metal sulfides, reducing the generation of intermediate polysulfides, and enabling the battery cell to have a higher specific capacity.

[0124] In some embodiments, the molar ratio of the aromatic compound to the alkali metal can be 1:(1-1.1).

[0125] In some embodiments, the molar ratio of elemental sulfur to alkali metal organosalt can be 1:(2-2.5).

[0126] In this application, the molar ratio of elemental sulfur to alkali metal organosalt refers to the molar ratio of the total molar amount of sulfur atoms in elemental sulfur to the molar ratio of the alkali metal organosalt. According to embodiments of this application, by limiting the molar ratio of alkali metal organosalt to elemental sulfur within the above-mentioned range, elemental sulfur and alkali metal organosalt can react fully to generate alkali metal sulfides in situ within the pores of porous carbon. When the amount of alkali metal organosalt is low, it is difficult to completely react the elemental sulfur in the pores of porous carbon, resulting in a lower content of effective active material, which is detrimental to the capacity utilization of the battery cell; when the amount of alkali metal organosalt is high, the alkali metal organosalt is prone to side reactions with porous carbon, affecting the conductivity of the battery cell.

[0127] In some embodiments, in step S20, the reaction temperature of the sulfur-carbon composite with the pre-reactant can be 25℃-100℃, for example, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, or any range of the above values; optionally, it can be 45℃-90℃. At lower temperatures, the sulfur in the pores of the porous carbon does not react completely with the pre-reactant, resulting in a limited content of alkali metal sulfides loaded in the porous carbon and a lower battery cell capacity. At higher reaction temperatures, the pre-reactant reacts with the porous carbon and readily reacts with the sulfur to produce byproducts, affecting the cycle performance of the battery cell.

[0128] In some embodiments, the reaction time between the sulfur-carbon complex and the pre-reactant can be 2h-48h, for example, 2h, 4h, 6h, 8h, 10h, 12h, 15h, 18h, 20h, 22h, 25h, 28h, 30h, 32h, 35h, 38h, 40h, 42h, 45h, 48h, or any range of the above values, and can be selected as 12h-30h.

[0129] In some embodiments, step S30 may include: using chemical vapor deposition (CVD) to form a carbon coating layer on at least a portion of the surface of the alkali metal sulfide-carbon complex using a carbon source.

[0130] According to the embodiments of this application, chemical vapor deposition can form a stable and uniform carbon coating layer on the surface of alkali metal sulfide-carbon composite. At the same time, the high temperature during the chemical vapor deposition process can oxidize and remove oxygen elements from the film layer formed by the reduced oxygen-containing active groups on the porous carbon surface, thereby further reducing the content of oxygen-containing active groups on the porous carbon surface, reducing side reactions, and improving the capacity performance of the battery cell.

[0131] In some embodiments, the carbon source may include one or more of gaseous hydrocarbons and liquid organic compounds.

[0132] As an example, gaseous hydrocarbons may include one or more of methane, ethane, propane, butane, ethylene, propylene, butene, and acetylene. Liquid organic compounds may include one or more of ethanol, benzene, and toluene.

[0133] In some embodiments, the positive electrode active material may further include one or more of lithium phosphate, layered lithium transition metal oxide, Prussian blue compounds, polyanionic compounds, and sodium transition metal oxide.

[0134] If the positive electrode active material is one or more of lithium phosphate and layered lithium transition metal oxide, then the positive electrode active material can be used in lithium-ion battery cells; if the positive electrode active material is one or more of Prussian blue compounds, polyanionic compounds, and sodium transition metal oxide, then the positive electrode material can be used in sodium-ion battery cells.

[0135] Lithium-containing phosphates may include one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and their respective modified compounds.

[0136] Examples of layered lithium-containing transition metal oxides may include one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds.

[0137] In some embodiments, the layered lithium-containing transition metal oxide may include Ni. The molar amount of Ni may account for more than 70% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide; optionally, the molar amount of Ni may account for more than 80% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide; more preferably, the molar amount of Ni may account for more than 90% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide.

[0138] The higher the Ni content in layered lithium-containing transition metal oxides, the higher the energy density of the battery cell.

[0139] In some embodiments, layered lithium-containing transition metal oxides may include Li a Ni b Co c M d O e A f Wherein, 0 < a ≤ 1.2; 0.8 ≤ b < 1; 0 < c < 1; 0 < d < 1; b + c + d = 1; 1 ≤ e ≤ 2; 0 ≤ f ≤ 1; M includes, but is not limited to, one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B; A includes, but is not limited to, one or more of N, F, S, and Cl. This can further improve the energy density of individual battery cells.

[0140] In some embodiments, as an example, layered lithium-containing transition metal oxides may include, but are not limited to, LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.06 Mn 0.04 O2, LiNi 0.92 Co 0.06 Mn 0.02 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2N 0.02 One or more of them.

[0141] During the charging and discharging process of a battery cell, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar Li content may change when the positive electrode active material is applied to the battery cell.

[0142] In some embodiments, as an example, sodium transition metal oxides may include, but are not limited to:

[0143] Na 1-x Cu h Fe k Mn l M 1 m O 2-y M 1 It is one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, and Ba, 0 <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2;

[0144] Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2, where M 2 It is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn and Ba, 0 <z≤0.1;

[0145] Na a Li b Ni c Mn d Fe e O2, of which 0.67 <a≤1,0<b<0.2,0<c<0.3,0.67<d+e<0.8,b+c+d+e=1。

[0146] In some embodiments, as an example, the polyanionic compound may include, but is not limited to:

[0147] A 1 f M 3 g (PO4) i O j X 1 3-j Where A is one or more of H, Li, Na, K, and NH4, and M 3is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, and Zn, X 1 is one or more of F, Cl, and Br, 0 < f ≤ 4, 0 < g ≤ 2, 1 ≤ i ≤ 3, 0 ≤ j ≤ 2;

[0148] Na n M 4 PO4X 2 , where M 4 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, X 2 is one or more of F, Cl, and Br, 0 < n ≤ 2;

[0149] Na p M 5 q (SO4)3, where M 5 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, 0 < p ≤ 2, 0 < q ≤ 2;

[0150] Na s Mn t Fe 3-t (PO4)2(P2O7), where 0 < s ≤ 4, 0 ≤ t ≤ 3, for example, t is 0, 1, 1.5, 2, or 3.

[0151] In some embodiments, by way of example, Prussian blue - like compounds may include, but are not limited to:

[0152] A u M 6 v [M 7 (CN)6] w ·xH2O, where A is H + , NH4 + , an alkali metal cation, or an alkaline earth metal cation, M 6 and M 7 are each independently one or more of transition metal cations, 0 < u ≤ 2, 0 < v ≤ 1, 0 < w ≤ 1, 0 < x < 6. For example, A is H + , Li + , Na + , K + , NH4 + , Rb + , Cs + , Fr + , Be 2+ , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ and Ra 2+One or more of them, M 6 and M 7 Each is an independently selected cation of one or more transition metal elements chosen from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, and W. Optionally, A is Li. + Na + and K + One or more of them, M 6 It is a cation of one or more transition metal elements selected from Mn, Fe, Co, Ni, and Cu, M 7 It is a cation of one or more transition metal elements selected from Mn, Fe, Co, Ni and Cu.

[0153] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0154] The modified compounds for the above-mentioned positive electrode active materials can be obtained by doping and / or surface coating of the positive electrode active materials.

[0155] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0156] In some embodiments, the adhesive has a weight percentage of 0.5% or greater in the positive electrode film layer, which is beneficial for obtaining good adhesion performance.

[0157] In some embodiments, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0158] 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 made by forming a metal material, such as aluminum, aluminum alloy, copper, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, on the polymer substrate. The polymer substrate may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and other substrates.

[0159] In some embodiments, the thickness of the positive current collector is from 4 μm to 20 μm. It is optionally from 6 μm to 18 μm, and more preferably from 8 μm to 16 μm.

[0160] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0161] [Negative electrode plate]

[0162] In some embodiments, the negative electrode includes a negative current collector.

[0163] In some embodiments, the negative electrode may include a conductive coating located on at least one side of the negative current collector.

[0164] In some embodiments, the conductive coating may include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] In some embodiments, the conductive coating may also include other additives. For example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc.

[0166] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one side of the polymeric material substrate. Examples of metal materials include, but are not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Examples of polymeric material substrates include, but are not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0167] The negative electrode sheet does not exclude other additional functional layers besides the conductive coating. For example, in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the conductive coating.

[0168] [Electrolytes]

[0169] A single battery cell includes an electrolyte.

[0170] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and an organic solvent.

[0171] In some embodiments, the electrolyte includes anion, which may include bis(fluorosulfonyl)imide anion (FSI). - ), bis(trifluoromethanesulfonyl)imide anion (TFSI) - ), dioxaborate anion (BOB) - ), difluorooxalate borate anion (DFOB) - ), difluorodioxanol phosphate anion (DFOP) - ), tetrafluorooxalate phosphate anion (TFOP) - ), difluorophosphate anion (PO2F2) - ), hexafluorophosphate anion (PF6) - ), tetrafluoroborate anion (BF4) - ), hexafluoroarsenate anion (AsF6) - One or more of the following: trifluoromethanesulfonate anion (CF3SO3-).

[0172] In some embodiments, the electrolyte includes cations, which may include one or more of lithium ions and sodium ions.

[0173] In some embodiments, the concentration of the electrolyte salt may be 0.3 mol / L or higher, optionally 0.7 mol / L or higher, and further optionally 4 mol / L or lower, optionally 2.5 mol / L or lower, or 1.7 mol / L or lower. When the concentration of the electrolyte salt is within the above range, the electrolyte can have a suitable ionic conductivity.

[0174] Organic solvents may include, but are not limited to, one or more of esters, ethers, sulfones, and nitriles. Esters may include, but are not limited to, one or more of carbonates, phosphate esters, carboxylic esters, sulfate esters, and sulfonates. Carbonates may include cyclic carbonates and / or chain carbonates; optionally, carbonates may include both cyclic and chain carbonates. Chain carbonates may include low-viscosity polar chain carbonates, aliphatic branched carbonates, etc.

[0175] As an example, organic solvents may include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), butene carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), dimethyl ether tetraethylene glycol (TEGDME), ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), trimethyl phosphate, 3-methoxypropionitrile, H(CF2)2OCH3, C4F9O CH3, H(CF2)2OCH2CH3, H(CF2)2OCH2CF3, H(CF2)2CH2O(CF2)2H, CF3CHFCF2OCH3, CF3CHFCF2OCH2CH3, 2-trifluoromethylhexafluoropropyl methyl ether, 2-trifluoromethylhexafluoropropyl ethyl ether, 2-trifluoromethylhexafluoropropyl propyl ether, 3-trifluoromethyloctafluorobutyl methyl ether, 3-trifluoromethyloctafluorobutyl ethyl ether, 3-trifluoromethyloctafluorobutyl propyl ether, 4-trifluoromethyl One or more of the following: decafluoropentyl methyl ether, 4-trifluoromethyl decafluoropentyl ethyl ether, 4-trifluoromethyl decafluoropentyl propyl ether, 5-trifluoromethyl dodecylfluorohexyl methyl ether, 5-trifluoromethyl dodecylfluorohexyl ethyl ether, 5-trifluoromethyl dodecylfluorohexyl propyl ether, 6-trifluoromethyl tetradecafluoroheptyl methyl ether, 6-trifluoromethyl tetradecafluoroheptyl ethyl ether, 6-trifluoromethyl tetradecafluoroheptyl propyl ether, 7-trifluoromethyl hexadecylfluorooctyl methyl ether, 7-trifluoromethyl hexadecylfluorooctyl ethyl ether, and 7-trifluoromethyl hexadecylfluorooctyl propyl ether.

[0176] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature power performance, etc.

[0177] [Isolation Component]

[0178] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0179] In some embodiments, the isolation chamber includes an isolation membrane. This application does not impose any particular limitation on the type of isolation membrane; any known porous membrane with good chemical and mechanical stability can be selected.

[0180] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation. The separator may be a single component located between the positive and negative electrodes, or it may be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating may also be applied to the surface of the separator.

[0181] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0182] Example

[0183] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0184] Example 1

[0185] Preparation of sulfide cathode materials

[0186] Take porous carbon Kojen Black (KB, pore volume 3.15 cm³). 3 / g, with a most probable pore size of 2.39nm, a theoretical sulfur loading of 86.1%, and a specific surface area of ​​1336m². 2 / g), KB and elemental sulfur were mixed evenly at a mass ratio of 65:35, and ball-milled at 1000 rpm for 6 hours using a high-energy ball mill. Then, the mixture was placed in a tube furnace filled with argon atmosphere and heated at 200°C for 12 hours. After being slowly cooled to room temperature, the mixture was taken out and quickly placed in a glove box to obtain the S@KB complex.

[0187] Take 5.4 g of biphenyl and dissolve it completely in 30 mL of dimethyl ethylene glycol (DME). Then add 0.8046 g of sodium metal and stir until the solid reacts and dissolves completely to obtain a pre-reactant containing sodium biphenyl.

[0188] In an argon-filled glove box, 0.788 g of the S@KB complex prepared above was added to the above pre-reactant. The molar ratio of sulfur to sodium biphenyl was 1:2.2. The mixture was stirred at 60°C for 24 h, centrifuged and filtered. The filter residue was washed repeatedly with DME and tetrahydrofuran (THF) until the supernatant was colorless and transparent. The powder was dried at 120°C on a heating platform to obtain the Na2S@KB complex.

[0189] The Na2S@KB composite prepared above was placed in a tube furnace for CVD coating. Bromobenzene was used as the carbon source, and the ratio of bromobenzene to argon atmosphere was adjusted to 1:1. The temperature was increased to 700℃ at a heating rate of 10℃ / min, and after holding at this temperature for 12h, the coated sulfide cathode material was obtained.

[0190] Positive electrode sheet

[0191] The sulfide cathode material, conductive carbon nanotubes (CNTs), conductive Super P, and binder polytetrafluoroethylene (PTFE) prepared above were weighed according to a mass ratio of 30:25:15:30. Under the inert atmosphere of a glove box, the active material and conductive agent were first mixed and stirred evenly. Then, the binder was added and the mixture was ground and mixed evenly to obtain a cathode slurry. The cathode slurry was evenly coated on the surface of the cathode current collector aluminum foil. The electrode sheet was repeatedly rolled and pressed under a heating condition of 80°C to make the electrode sheet as smooth and flat as possible until the electrode sheet thickness was about 150 μm. Finally, the electrode sheet was cut to obtain the cathode sheet. The coating amount per unit area of ​​the cathode sheet was 0.25 g / 1540.25 mm. 2 .

[0192] Negative electrode sheet

[0193] Carbon nanotubes (CNTs) and sodium carboxymethyl cellulose (CMC-Na) were thoroughly mixed in deionized water at a weight ratio of 1:1 to form a conductive slurry. The conductive slurry was then coated onto the surface of a copper foil current collector with a thickness of 2 μm. After drying, the negative electrode sheet was obtained.

[0194] Separating membrane

[0195] A 12μm thick polypropylene membrane was used as the separator.

[0196] electrolyte

[0197] In an argon atmosphere glove box (water content less than 0.1 ppm, oxygen content less than 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI) electrolyte salt was added to the organic solvent tetraethylene glycol dimethyl ether and stirred until homogeneous to obtain an electrolyte solution with a NaFSI mass concentration of 12.5%.

[0198] battery cell

[0199] The positive electrode, negative electrode, and separator are stacked in sequence and injected with electrolyte to obtain a single negative electrode-free battery cell.

[0200] Example 2-10

[0201] The preparation method of the battery cell is similar to that in Example 1. The difference is that the composition parameters of the sulfide cathode material are different. For details of the parameter adjustments, please refer to Table 1.

[0202] Table 1

[0203] Examples 11-18

[0204] The preparation method of the battery cell is similar to that in Example 1. The difference is that the preparation parameters of the sulfide cathode material are different. For details of the parameter adjustments, please refer to Table 2.

[0205] Table 2

[0206] Comparative Example 1

[0207] The preparation method of the battery cell is similar to that in Example 1, except that the preparation method of the sulfide cathode material is different, as detailed below:

[0208] Porous carbon KB was mixed with elemental sulfur, and the mass ratio of porous carbon to sulfur was controlled at 65:35 to obtain the S@KB complex.

[0209] Take 5.4 g of biphenyl and dissolve it completely in 30 mL of dimethyl ethylene glycol (DME). Then add 0.8046 g of sodium metal and stir until the solid reacts and dissolves completely to obtain a pre-reactant containing sodium biphenyl.

[0210] In an argon-filled glove box, 0.788 g of the S@KB complex prepared above was added to the above pre-reaction agent. The molar ratio of sulfur to sodium biphenyl was 1:2.2. The mixture was stirred at 60°C for 24 h, centrifuged and filtered. The filter residue was washed repeatedly with DME and tetrahydrofuran (THF) until the supernatant was colorless and transparent. The powder was dried at 120°C on a heating platform to obtain the Na2S@KB complex.

[0211] The Na2S@KB composite prepared above was placed in a tube furnace for CVD coating. Bromobenzene was used as the carbon source, and the ratio of bromobenzene to argon atmosphere was adjusted to 1:1. The temperature was increased to 700℃ at a heating rate of 10℃ / min, and after holding at this temperature for 12h, the coated sulfide cathode material was obtained.

[0212] Comparative Example 2

[0213] The preparation method of the battery cell is similar to that in Example 1, except that the preparation method of the sulfide cathode material is different, as detailed below:

[0214] Porous carbon KB was taken and mixed with elemental sulfur at a mass ratio of 65:35. The mixture was then ball-milled at 1000 rpm for 6 hours using a high-energy ball mill. The mixture was then placed in a tube furnace filled with argon atmosphere and heated at 200°C for 12 hours. After being slowly cooled to room temperature, the mixture was removed and quickly placed in a glove box to obtain the S@KB composite.

[0215] Take 5.4 g of biphenyl and dissolve it completely in 30 mL of dimethyl ethylene glycol (DME). Then add 0.8046 g of sodium metal and stir until the solid reacts and dissolves completely to obtain a pre-reactant containing sodium biphenyl.

[0216] In an argon-filled glove box, 0.788 g of the S@KB composite prepared above was added to the pre-reactant, with a sulfur element to biphenyl sodium molar ratio of 1:2.2. The mixture was stirred at 60°C for 24 h, centrifuged and filtered, and the filter residue was repeatedly washed with DME and tetrahydrofuran (THF) until the supernatant was colorless and transparent. The powder was dried at 120°C on a heating stage to obtain the sulfide cathode material.

[0217] Comparative Example 3

[0218] The preparation method of the battery cell is similar to that in Example 1, except that the preparation method of the sulfide cathode material is different, as detailed below:

[0219] Porous carbon KB was mixed with sodium sulfide, and the mass ratio of porous carbon to sulfur was controlled at 65:35. The mixture was ball-milled at 1000 rpm for 6 hours using a high-energy ball mill. Then it was placed in a tube furnace filled with argon atmosphere and heated at 200℃ for 12 hours. After being slowly cooled to room temperature, it was taken out and quickly placed in a glove box to obtain the Na2S@KB complex.

[0220] The sodium sulfide-KB composite prepared above was placed in a tube furnace for CVD coating. Bromobenzene was used as the carbon source, and the ratio of bromobenzene to argon atmosphere was adjusted to 1:1. The temperature was increased to 700℃ at a heating rate of 10℃ / min, and after holding at this temperature for 12h, the coated sulfide cathode material was obtained.

[0221] Test section

[0222] 1. First-cycle capacity of a single battery cell under conventional electrolyte conditions

[0223] At 25℃, the battery cell is charged to 2.8V at a constant current of 0.2C, and the initial charging capacity is recorded. The ratio of the initial discharge capacity to the mass of the positive electrode material is recorded as the initial charging specific capacity C0. After resting for 5 minutes, the cell is discharged to 1.0V at 2C under 25℃, and the initial discharge capacity is recorded. The ratio of the initial discharge capacity to the mass of the positive electrode material is recorded as the initial discharge specific capacity D0.

[0224] 2. Cycle performance of individual battery cells under conventional electrolyte conditions

[0225] At 25℃, the battery cell is charged at a constant current of 0.2C to 2.8V, left to stand for 5 minutes, and then discharged at 2C to 1.0V. The resulting capacity is recorded as the initial capacity D0. The above charge and discharge steps are repeated for the battery cell, and the discharge capacity D10 of the battery is recorded after the 10th cycle. The battery capacity retention rate P10 = D10 / D0*100%.

[0226] 3. Sulfur dissolution rate of the positive electrode sheet

[0227] The state in which a battery cell has not undergone charge-discharge cycles is recorded as the initial state. In the initial state, the battery cell is disassembled to obtain the positive electrode plate. The initial sulfur content of the positive electrode plate is determined by ICP as m1. After the battery cell undergoes 10 charge-discharge cycles in a conventional electrolyte, the battery cell is disassembled to obtain the cycled positive electrode plate. The sulfur content of the cycled positive electrode plate is determined by ICP as m2. The sulfur dissolution rate (%) = (m1-m2) / m1×100%.

[0228] 4. Initial cycle capacity of cells with locally high-concentration electrolyte

[0229] In an argon atmosphere glove box with a water content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm, NaFSI, DME, and TTE (1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether) were mixed and stirred evenly in a molar ratio of 1:1.2:1 to obtain a locally high-concentration electrolyte. The locally high-concentration electrolyte was used to replace the conventional electrolyte to obtain a battery cell.

[0230] At 25℃, the battery cell is charged to 2.8V at a constant current of 0.05C, and the initial charging capacity is recorded. The ratio of the initial discharge capacity to the mass of the positive electrode material is recorded as the initial charging specific capacity C0. After standing for 5 minutes, the cell is discharged to 1.0V at 0.05C at 25℃, and the initial discharge capacity is recorded. The ratio of the initial discharge capacity to the mass of the positive electrode material is recorded as the initial discharge specific capacity D0.

[0231] 5. Cycle performance of individual cells under locally high electrolyte concentration

[0232] At 25°C, a single battery cell is charged to 2.8V at a constant current of 0.05C, allowed to stand for 5 minutes, and then discharged to 1.0V at 0.05C. The resulting capacity is recorded as the initial capacity D0. The above charge-discharge steps are repeated for the battery cell, and the discharge capacity D of the battery after the 10th cycle is recorded. 10 Battery capacity retention rate P 10 =D 10 / D0*100%.

[0233] The test results are detailed in Table 3.

[0234] Table 3

[0235] Combining Example 1 and Comparative Examples 1-3, by generating sulfides in situ within the pores of porous carbon and confining them within these pores, the capacity and cycle performance of individual battery cells can be significantly improved. This is because confining the sulfides within the pores of the porous carbon reduces sulfur dissolution during charge-discharge cycles. Simultaneously, during the in-situ sulfide generation process, the pre-reactant can reduce at least some of the oxygen-containing active groups on the surface of the porous carbon, thereby lowering the oxygen content of the sulfide cathode material. The high temperature during the CVD coating process further removes unstable oxygen-containing active groups, thus reducing the reaction consumption of active metals by these groups. Through the combined effect of confining and fixing the sulfides and reducing the consumption of active metals, the battery cells exhibit higher capacity and improved cycle performance.

[0236] Figure 4 shows the XRD patterns of the sulfide cathode materials prepared in Example 1 and Comparative Example 1 of this application. It can be seen that the sodium sulfide content detected on the surface of the sulfide cathode material in Example 1 is relatively low, indicating that sodium sulfide is more distributed in the channels of porous carbon; while in Comparative Example 1, the sulfide cathode material is more distributed on the surface of porous carbon. Further, combining the morphology and elemental distribution of the sulfide cathode materials in Figures 5 and 6, it can be seen that the distribution of S, Na and C elements is consistent in Example 1, while in Comparative Example 1, S and Na elements are distributed on the periphery of porous carbon. This further illustrates that in the sulfide cathode material of Example 1 of this application, sodium sulfide is fully filled in the channels of porous carbon.

[0237] By combining implementations 1-5, adjusting the ratio of actual sulfur content to the theoretical sulfur loading of porous carbon can further improve the capacity of individual battery cells and enhance cycle performance. When the actual sulfur content is high, sulfur cannot be completely confined within the pores of porous carbon, resulting in greater sulfur dissolution during battery cell cycling. This leads to a decrease in battery cell capacity and poorer cycle performance due to the consumption of active materials. Conversely, when the actual sulfur content is low, the sulfide content of the cathode material is low, resulting in a lower capacity of the individual battery cells.

[0238] In conjunction with Examples 6 and 7, by adjusting the type of porous carbon and adjusting the pore volume and most probable pore size of the porous carbon, the sulfur loading of the porous carbon can be further increased, thereby further improving the capacity of the battery cell and improving the cycle performance.

[0239] In conjunction with Examples 8 and 9, adjusting the thickness of the carbon coating layer can further improve the capacity and cycle performance of the battery cells. A thinner carbon coating layer results in poorer sulfur fixation, increased sulfur dissolution, and affects the cycle performance of the battery cells; a thicker carbon coating layer hinders the electrochemical reaction process, easily leading to poorer kinetics and lower battery cell capacity.

[0240] In conjunction with Examples 10-13, by adjusting the concentration of alkali metal organosalts during the preparation of sulfide cathode materials, it is possible to ensure that the sulfur element filling the porous carbon reacts as completely as possible to form sulfides, thereby improving the battery capacity and cycle performance. When the concentration of alkali metal organosalts is low, the sulfur element in the porous carbon channels does not react completely, resulting in a low sulfide content in the cathode material and a low single-cell capacity. When the concentration of alkali metal organosalts is high, they react with the porous carbon, leading to a higher single-cell charging capacity and a tendency to react to form unstable NaPS, resulting in a decrease in the single-cell cycle performance.

[0241] In conjunction with Examples 14-17, the cycle performance of the battery cell can be further improved by adjusting the reaction temperature and reaction time of the pre-reactant during the preparation process. When the reaction temperature is low or the reaction time is short, the elemental sulfur filling the porous carbon channels cannot react completely, resulting in a low sulfide content in the cathode material and a low battery cell capacity. When the reaction temperature is high or the reaction time is long, the pre-reactant reacts with the porous carbon and easily generates unstable NaPS, leading to a decrease in the cycle performance of the battery cell.

[0242] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising a sulfide positive electrode material, the sulfide positive electrode material comprising: The core comprises porous carbon and alkali metal sulfides filling the pores of the porous carbon; A carbon-coated material is used to coat at least a portion of the surface of the core; The oxygen content of the sulfide cathode material is less than or equal to 0.05%.

2. The battery cell according to claim 1, wherein, The theoretical sulfur loading of the porous carbon is M0, and the mass content of sulfur in the core is M1, where 0.2 ≤ M1 / M0 ≤ 0.

95.

3. The battery cell according to claim 2, wherein, 0.3≤M1 / M0≤0.

8.

4. The battery cell according to claim 2 or 3, wherein, 50％≤M0≤90％。 5. The battery cell according to any one of claims 1-4, wherein, The porous carbon satisfies at least one of the following conditions (1)-(3): (1) The most probable pore size of the porous carbon is 1 nm-5 nm; (2) The porous carbon has a pore volume of 0.3 cm³. 3 / g-4cm 3 / g; (3) The specific surface area of ​​the porous carbon is 400 m². 2 / g-1500m 2 / g.

6. The battery cell according to any one of claims 1-5, wherein, The porous carbon includes one or more of mesoporous carbon and microporous carbon.

7. The battery cell according to any one of claims 1-6, wherein, The alkali metal sulfides include one or both of lithium sulfide and sodium sulfide.

8. The battery cell according to any one of claims 1-7, wherein, The carbon coating material forms a carbon coating layer on at least a portion of the surface of the core, the thickness of the carbon coating layer being 3nm-100nm.

9. The battery cell according to any one of claims 1-8, wherein, The battery cell is a negative electrode-free battery cell.

10. A battery device comprising a battery cell according to any one of claims 1 to 9.

11. An electrical device comprising a battery cell according to any one of claims 1 to 9 or a battery device according to claim 10.

12. A positive electrode active material, comprising a sulfide positive electrode material, wherein the sulfide positive electrode material comprises: The core comprises porous carbon and alkali metal sulfides filling the pores of the porous carbon; A carbon-coated material is used to coat at least a portion of the surface of the core; The oxygen content of the sulfide cathode material is less than or equal to 0.05%.

13. A method for preparing a positive electrode active material, comprising the following steps: Porous carbon is mixed with elemental sulfur and heated to melt and fill the pores of the porous carbon, thus obtaining a sulfur-carbon composite. A pre-reactant containing an alkali metal organic salt is provided. The sulfur-carbon complex is mixed with the pre-reactant and reacted with elemental sulfur in the pores of the porous carbon to generate alkali metal sulfides in situ, thereby obtaining an alkali metal sulfide-carbon complex. A carbon source is provided such that the carbon source forms a carbon coating layer on at least a portion of the surface of the alkali metal sulfide-carbon complex.

14. The preparation method according to claim 13, wherein, In the step of heating the porous carbon and elemental sulfur mixture, the heating temperature is 100℃-200℃.

15. The preparation method according to claim 13 or 14, wherein, The step of providing a pre-reactant containing an alkali metal organometallic salt includes: The aromatic compound is reacted with an alkali metal in a solvent to obtain the pre-reactant.

16. The preparation method according to claim 15, wherein, The concentration of the alkali metal organic salt in the pre-reactant is 0.5 mol / L to 3 mol / L.

17. The preparation method according to claim 15 or 16, wherein, The alkali metal includes one or both of lithium and sodium metals; and / or The solvent includes one or more of ethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

18. The preparation method according to any one of claims 15-17, wherein, The molar ratio of the aromatic compound to the alkali metal is 1:(1-1.1).

19. The preparation method according to any one of claims 13-18, wherein, The molar ratio of the elemental sulfur to the alkali metal organic salt is 1:(2-2.5).

20. The preparation method according to any one of claims 13-19, wherein, The step of mixing the sulfur-carbon complex with the pre-reactant and reacting it with elemental sulfur in the pores of the porous carbon to generate alkali metal sulfides in situ satisfies the following: The reaction temperature of the sulfur-carbon complex with the pre-reactant is 25℃-100℃; and / or The reaction time between the sulfur-carbon complex and the pre-reactant is 2h-48h.

21. The preparation method according to any one of claims 13-20, wherein, The step of forming a carbon coating layer on at least a portion of the surface of the alkali metal sulfide-carbon complex using the carbon source includes: using chemical vapor deposition to form a carbon coating layer on at least a portion of the surface of the alkali metal sulfide-carbon complex.

22. The preparation method according to any one of claims 13-21, wherein, The carbon source includes one or more of gaseous hydrocarbons and liquid organic compounds.

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