Positive plate, preparation method thereof and lithium-selenium battery

Abstract

The embodiment of the invention relates to a positive plate, a preparation method thereof and a lithium-selenium battery, the positive plate comprises a current collector, and a first active material layer and a second active material layer which are sequentially laminated on at least one side surface of the current collector, and the first active material layer is arranged between the current collector and the second active material layer; the first active material layer comprises a sulfur-selenium compound; the second active substance layer comprises a selenium-carbon composite material, a carbon material in the selenium-carbon composite material has a porous structure, and selenium is distributed in pores and / or the surface of the carbon material. Through the double-layer structure design of the first active material layer and the second active material layer, the conductivity, the cycling stability and the reversibility of the positive plate can be improved, and meanwhile, the high specific capacity of the positive plate is considered.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a positive electrode sheet, a preparation method thereof, and a lithium-selenium battery. Background Art

[0002] Lithium-selenium batteries have a relatively high theoretical volumetric energy density (about 2528 Wh / L) and mass energy density (about 1155 Wh / Kg), which can effectively extend the service life of the battery and reduce the battery volume, making lithium-selenium batteries have great application potential in the fields of portable electronic devices and electric vehicles. In addition, selenium (Se) has a relatively high electronic conductivity (1×10 -5 S / cm), which is beneficial to improving the electrochemistry reaction kinetics and the effective utilization rate of materials. Moreover, Se has a high melting point of up to about 221 °C, which can better ensure the safety of the battery during operation at high temperatures.

[0003] However, based on the conversion reaction mechanism of Se in lithium-selenium batteries (Se→Li2Se6→Li2Se), during the charge and discharge process, an intermediate discharge product Li2Se6 will be generated. Li2Se6 dissolves in the electrolyte and is prone to the shuttle effect, attaching to the surface of the negative electrode. This will not only cause the loss of the positive electrode active material, but also trigger side reactions on the negative electrode side, resulting in a rapid decay of the battery capacity. Therefore, how to improve the electrochemical performance of lithium-selenium batteries has become a technical problem that urgently needs to be solved at present. Summary of the Invention

[0004] In view of this, the embodiments of the present application provide a positive electrode sheet, a preparation method thereof, and a lithium-selenium battery to solve at least one problem in the background art.

[0005] In a first aspect, the embodiments of the present application provide a positive electrode sheet, which includes a current collector and a first active material layer and a second active material layer sequentially stacked on at least one surface of the current collector, and the first active material layer is disposed between the current collector and the second active material layer;

[0006] The first active material layer includes a sulfur-selenium compound;

[0007] The second active material layer includes a selenium-carbon composite material, and the carbon material in the selenium-carbon composite material has a porous structure, and selenium is distributed in the pores and / or on the surface of the carbon material.

[0008] Combined with the first aspect of the present application, in an optional embodiment, the chemical formula of the sulfur-selenium compound is Se x S y , where x:y = 1:(2 to 10).

[0009] In connection with the first aspect of the present application, in an optional embodiment, the selenium-carbon composite material satisfies at least one of the following characteristics:

[0010] (1) The mass ratio of the selenium to the carbon material is (7-8):(2-3);

[0011] (2) The pore diameter of the carbon material is 6 nm to 13 nm;

[0012] (3) The carbon material includes at least one of porous carbon nanotubes, porous carbon fibers, porous graphene, porous conductive carbon black, porous graphite, porous resin carbon, porous biomass carbon, and activated carbon.

[0013] In connection with the first aspect of the present application, in an optional embodiment, the positive electrode sheet satisfies at least one of the following characteristics:

[0014] (1) The thickness of the first active material layer is 30 μm to 40 μm;

[0015] (2) The thickness of the second active material layer is 40 μm to 50 μm;

[0016] (3) The first active material layer further includes a first conductive agent and a first binder, and the mass ratio of the sulfur-selenium compound, the first conductive agent, and the first binder is (7-8):(1-2):1;

[0017] (4) The second active material layer further includes a second conductive agent and a second binder, and the mass ratio of the selenium-carbon composite material, the second conductive agent, and the second binder is (7-8):(1-2):1.

[0018] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode sheet, and the method includes the following steps:

[0019] S1: Prepare a first slurry and a second slurry. The first slurry includes a sulfur-selenium compound, and the second slurry includes a selenium-carbon composite material. The carbon material in the selenium-carbon composite material has a porous structure, and selenium is distributed in the pores and / or on the surface of the carbon material;

[0020] S2: Stack and coat the first slurry and the second slurry on at least one surface of the current collector in such a way that the first slurry is closer to the current collector than the second slurry, and obtain the positive electrode sheet after drying.

[0021] In connection with the second aspect of the present application, in an optional embodiment, preparing the first slurry includes:

[0022] Add the sulfur-selenium compound, the first conductive agent, and the first binder into a first solvent. After mixing evenly, the first slurry is obtained. Optionally, the mass ratio of the sulfur-selenium compound, the first conductive agent, and the first binder is (7-8):(1-2):1. Optionally, the chemical formula of the sulfur-selenium compound is Se x S y , where x:y = 1:(2-10).

[0023] Combined with the second aspect of the present application, in an alternative embodiment, preparing the second slurry includes:

[0024] Add the selenium-carbon composite material, the second conductive agent, and the second binder into a second solvent. After mixing evenly, the second slurry is obtained. Optionally, the mass ratio of the selenium-carbon composite material, the second conductive agent, and the second binder is (7-8):(1-2):1.

[0025] Combined with the second aspect of the present application, in an alternative embodiment, the preparation method of the selenium-carbon composite material includes:

[0026] Under a protective gas atmosphere, mix selenium with a carbon material and then perform ball milling treatment to obtain a mixture;

[0027] After compacting the mixture, under a protective gas atmosphere, perform calcination treatment on the mixture. After cooling, the selenium-carbon composite material is obtained.

[0028] Combined with the second aspect of the present application, in an alternative embodiment, the method satisfies at least one of the following characteristics:

[0029] (1) The mass ratio of the selenium to the carbon material is (7-8):(2-3);

[0030] (2) The pore diameter of the carbon material is 6 nm to 13 nm;

[0031] (3) The carbon material includes at least one of carbon nanotubes, ordered mesoporous carbon, carbon fiber, graphene, and Ketjen black;

[0032] (4) The time of the ball milling treatment is 22 h to 26 h;

[0033] (5) The pressure of the compaction is 100 MPa to 120 MPa, the time of a single compaction is 20 min to 25 min; the number of compaction times is 3 to 5 times;

[0034] (6) The temperature of the calcination treatment is 260 °C to 280 °C, and the time of the calcination treatment is 20 h to 32 h.

[0035] In a third aspect, an embodiment of the present application provides a lithium-selenium battery, including the positive electrode sheet according to any one of the first aspect or the positive electrode sheet prepared by the preparation method according to any one of the second aspect.

[0036] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0037] The positive electrode sheet, its preparation method and the lithium-selenium battery provided by the embodiments of the present application. The positive electrode sheet includes a current collector and a first active material layer and a second active material layer sequentially stacked on at least one surface of the current collector. The first active material layer is disposed between the current collector and the second active material layer; the first active material layer includes a sulfur-selenium compound; the second active material layer includes a selenium-carbon composite material, and the carbon material in the selenium-carbon composite material has a porous structure, and selenium is distributed in the pores and / or on the surface of the carbon material. In the embodiments of the present application, the first active material layer includes a sulfur-selenium compound. Sulfur has a high theoretical specific capacity, and selenium has a high electronic conductivity. Through the combination of sulfur and selenium, the conductivity of the positive electrode sheet can be ensured and the specific capacity of the positive electrode sheet can be improved; the second active material layer includes a selenium-carbon composite material. Through the combination of selenium and the carbon material with a porous structure, the specific surface area of the positive electrode sheet can be significantly increased, thereby increasing the reaction active sites, promoting the infiltration of the electrolyte, and improving the electrochemistry reaction kinetics of the positive electrode sheet. Moreover, through the adsorption and confinement effect of the carbon material, the dissolution and shuttle of intermediate discharge products such as polyselenides and polysulfides into the electrolyte can be inhibited, and thus the shuttle effect can be effectively inhibited, reducing the loss of the positive electrode active material and the side reaction on the negative electrode side. Therefore, through the double-layer structure design of the first active material layer and the second active material layer, while improving the conductivity, cycle stability and reversibility of the positive electrode sheet, the high specific capacity of the positive electrode sheet can be taken into account.

[0038] The additional aspects and advantages of the present application will be partially given in the following description, partially become apparent from the following description, or be understood through the practice of the present application. Description of the Drawings

[0039] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation to the present application. In the drawings:

[0040] Figure 1 It is a schematic cross-sectional structure diagram of a positive electrode sheet provided by an embodiment of the present application;

[0041] Figure 2 It is a schematic flow diagram of a preparation method of a positive electrode sheet provided by an embodiment of the present application;

[0042] Figure 3 It is a schematic flow diagram of a preparation method of a selenium-carbon composite material provided by an embodiment of the present application. Detailed implementation manners

[0043] To make the technical solutions and beneficial effects of the present invention more obvious and understandable, the following will provide a detailed description by combining the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions indicated in the following embodiments are generally in accordance with conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0044] In the following description, a large number of specific details are given to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features well known to those skilled in the art are not described; that is, not all features of the actual embodiments are described here, and the well-known functions and steps are not described in detail.

[0045] The purpose of the terms used herein is only to describe specific embodiments and not to limit the present application. When used herein, the singular forms of "a", "an" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, determine the presence of the described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. When used herein, the term "and / or" includes any and all combinations of the related listed items.

[0046] To thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solutions of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may also have other implementation manners.

[0047] Unless otherwise defined, the technical and scientific terms used in the present application have the same meanings as those of the technical and scientific terms in the technical field to which the present application belongs.

[0048] For those technical or conditions not specified in the following embodiments, they are generally in accordance with the conventional techniques or conditions described in the literature in the art, or in accordance with the conditions recommended in the product manual and by the manufacturer. The numerical ranges in the following embodiments all include the endpoint values.

[0049] In the related art, the positive electrode active material of a lithium-selenium battery uses a composite material of carbon and selenium to utilize the confinement effect of the carbon material and slow down the dissolution of intermediate discharge products such as polyselenides (e.g., Li2Se6) into the electrolyte, thereby inhibiting the occurrence of the shuttle effect. However, the introduction of the carbon material will significantly reduce the mass and volume energy density of the lithium-selenium battery, which is contrary to the goal of using selenium as the positive electrode material to improve the battery energy density.

[0050] Based on this, an embodiment of the present application provides a positive electrode sheet, as Figure 1 shown. The positive electrode sheet includes a current collector 100 and a first active material layer 201 and a second active material layer 202 that are sequentially stacked on at least one surface of the current collector 100. The first active material layer 201 is disposed between the current collector 100 and the second active material layer 202; the first active material layer 201 includes a sulfur-selenium compound; the second active material layer 202 includes a selenium-carbon composite material, and the carbon material in the selenium-carbon composite material has a porous structure, and selenium is distributed in the pores and / or on the surface of the carbon material.

[0051] In the positive electrode sheet of the embodiment of the present application, the first active material layer 201 includes a sulfur-selenium compound. Since sulfur has a high theoretical specific capacity (1675 mAh / g) and selenium has a high electronic conductivity, through the combination of sulfur and selenium, the conductivity of the positive electrode sheet can be ensured and the specific capacity of the positive electrode sheet can be improved; the second active material layer 202 includes a selenium-carbon composite material. Through the combination of selenium and the carbon material with a porous structure, the specific surface area of the positive electrode sheet can be significantly increased, thereby increasing the reaction active sites, promoting the infiltration of the electrolyte, and improving the electrochemical reaction kinetics of the positive electrode sheet. Moreover, through the adsorption and confinement effects of the carbon material, the dissolution and shuttle of intermediate discharge products such as polyselenides and polysulfides into the electrolyte can be inhibited, and thus the shuttle effect can be effectively inhibited, reducing the loss of the positive electrode active material and side reactions on the negative electrode side. Therefore, through the double-layer structure design of the first active material layer 201 and the second active material layer 202, while improving the conductivity, cycle stability and reversibility of the positive electrode sheet, the high specific capacity of the positive electrode sheet can be taken into account.

[0052] It should be noted that Figure 1 the sequential stacking of the first active material layer 201 and the second active material layer 202 on one surface of the current collector 100 in

[0053] is only an example. In some specific embodiments, the first active material layer 201 and the second active material layer 202 can be sequentially stacked on multiple surfaces of the current collector 100. For example, they can be sequentially stacked on opposite surfaces of the current collector 100.

[0053] In some embodiments, the chemical formula of the sulfur-selenium compound in the first active layer can be Se x S y, where x:y = 1:(2 - 10). In a specific embodiment, the sulfur-selenium compound may include SeS2. Since SeS2 has more excellent electrochemical properties and a more suitable sulfur-selenium ratio, it can better improve the specific capacity and cycling performance of the positive electrode sheet.

[0054] In the implementation of this application, in the selenium-carbon composite material in the second active material layer 202, the carbon material with a porous structure can provide a "skeleton" for selenium, improve the conductivity, ensure that there is enough active material in the positive electrode sheet, and at the same time provide a large electrode reaction area, increasing the reaction active sites. Selenium can be distributed in the pores and / or on the surface of the carbon material. In a specific embodiment, selenium is distributed in the pores of the carbon material. In this way, not only can a large amount of selenium be accommodated, thereby further improving the specific capacity of the positive electrode sheet, but also the volume expansion of the selenium-based material during the battery cycle can be better inhibited by the carbon material, and the shuttle effect of the intermediate discharge product can be better inhibited, thereby further improving the cycling stability and reversibility of the positive electrode sheet.

[0055] It can be understood that in the selenium-carbon composite material, when the mass ratio of selenium to the carbon material is too high, the proportion of selenium is too high and the proportion of the carbon material is too low. In this way, the improvement of the specific surface area of the positive electrode sheet is limited, and the inhibitory effect on the shuttle effect is limited; when the mass ratio of selenium to the carbon material is too low, the proportion of selenium is too low and the proportion of the carbon material is too high. In this way, it is not conducive to the improvement of the specific capacity of the positive electrode sheet. Therefore, in some specific embodiments, the mass ratio of selenium to the carbon material can be (7 - 8):(2 - 3), for example, it can be 8:2, 7:2, 8:3, 7:3 or any value between any two of the above numerical ranges. In this way, the specific capacity, cycling stability and reversibility of the positive electrode sheet can be better balanced.

[0056] When the pore size of the carbon material is too large, it is not conducive to inhibiting the shuttle effect of the intermediate discharge product; when the pore size of the carbon material is too small, it will limit the improvement of the specific surface area of the positive electrode sheet, and thus is not conducive to the increase of the reaction active sites. Therefore, in some specific embodiments, in the selenium-carbon composite material, the pore size of the carbon material can be 6 nm - 13 nm. In this way, while increasing the selenium loading, the shuttle effect of the intermediate discharge product can be effectively inhibited, thereby further improving the specific capacity and cycling performance of the positive electrode sheet.

[0057] Exemplarily, the carbon material may include at least one of porous carbon nanotubes, porous carbon fibers, porous graphene, porous conductive carbon black, porous graphite, porous resin carbon, porous biomass carbon, and activated carbon.

[0058] In the embodiments of the present application, when the thickness of the first active material layer 201 is too thin, it is not conducive to the improvement of the specific capacity of the positive electrode sheet; when the thickness of the first active material layer 201 is too thick, it will extend the transmission path of active ions, which is not conducive to the improvement of the rate performance and cycling performance of the positive electrode sheet. Therefore, in some specific embodiments, the thickness of the first active material layer 201 can be 30 μm to 40 μm, for example, it can be 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm or any value between any two of the above numerical ranges.

[0059] In the embodiments of the present application, when the thickness of the second active material layer 202 is too thin, it is not conducive to the improvement of the electrochemistry reaction kinetics of the positive electrode sheet, and the effects of suppressing the shuttle effect of the intermediate discharge product and the volume expansion of the selenium-based material are limited; when the thickness of the second active material layer 202 is too thick, it will extend the transmission path of active ions, which is not conducive to the improvement of the rate performance and cycling performance of the positive electrode sheet. Therefore, in some specific embodiments, the thickness of the second active material layer 202 can be 40 μm to 50 μm, for example, it can be 40 μm, 42 μm, 44 μm, 46 μm, 48 μm, 50 μm or any value between any two of the above numerical ranges.

[0060] In some embodiments, the first active material layer 201 further includes a first conductive agent and a first binder, and the mass ratio of the sulfur-selenium compound, the first conductive agent and the first binder can be (7-8):(1-2):1. Controlling the mass ratio of the sulfur-selenium compound, the first conductive agent and the first binder within the above range can, while ensuring the mechanical strength and conductivity of the positive electrode sheet, further improve the specific capacity of the positive electrode sheet, and further improve the energy density of the battery.

[0061] In the embodiments of the present application, there is no particular limitation on the types of the first conductive agent and the first binder, and binders and conductive agents well-known to those skilled in the art and applicable to positive electrode sheets can be used. Exemplarily, the first conductive agent can include conductive carbon black. The first binder can include polyvinylidene fluoride (PVDF).

[0062] In some embodiments, the second active material layer 202 further includes a second conductive agent and a second binder, and the mass ratio of the selenium-carbon composite material, the second conductive agent and the second binder can be (7-8):(1-2):1. Controlling the mass ratio of the selenium-carbon composite material, the second conductive agent and the second binder within the above range can, while ensuring the mechanical strength and conductivity of the positive electrode sheet, further improve the cycling stability and reversibility of the positive electrode sheet, and further improve the life of the battery.

[0063] In the embodiments of the present application, there are no specific limitations on the types of the second conductive agent and the second binder. Binders and conductive agents well-known to those skilled in the art and applicable to the positive electrode sheet can be used. Exemplarily, the second conductive agent may include conductive carbon black. The second binder may include polyvinylidene fluoride. Of course, the types of the first conductive agent and the second conductive agent may be the same or different. The types of the first binder and the second binder may be the same or different.

[0064] The embodiments of the present application also provide a method for preparing a positive electrode sheet. Please refer to Figure 2 , the method for preparing a positive electrode sheet provided by the embodiments of the present application includes the following steps:

[0065] S1: Prepare a first slurry and a second slurry. The first slurry includes a sulfur-selenium compound, and the second slurry includes a selenium-carbon composite material. The carbon material in the selenium-carbon composite material has a porous structure, and selenium is distributed in the pores and / or on the surface of the carbon material;

[0066] S2: Stack and coat the first slurry and the second slurry on at least one surface of the current collector in such a way that the first slurry is closer to the current collector than the second slurry, and obtain a positive electrode sheet after drying.

[0067] In the embodiments of the present application, by coating the first slurry and the second slurry on the current collector, a first active material layer (corresponding to the first slurry) and a second active material layer (corresponding to the second slurry) can be formed on the current collector in a stacked manner. The first active material layer includes a sulfur-selenium compound. Sulfur has a high theoretical specific capacity, and selenium has a high electronic conductivity. Through the combination of sulfur and selenium, the conductivity of the positive electrode sheet can be ensured and the specific capacity of the positive electrode sheet can be improved; the second active material layer includes a selenium-carbon composite material. Through the combination of selenium and the carbon material with a porous structure, the specific surface area of the positive electrode sheet can be significantly increased, thereby increasing the reaction active sites, promoting the infiltration of the electrolyte, and improving the electrochemistry reaction kinetics of the positive electrode sheet. Moreover, through the adsorption and confinement effects of the carbon material, the dissolution and shuttling of intermediate discharge products such as polyselenides and polysulfides into the electrolyte can be inhibited, and thus the shuttling effect can be effectively inhibited, reducing the loss of the positive electrode active material and the side reactions on the negative electrode side. Therefore, through the double-layer structure design of forming the first active material layer and the second active material layer by coating, while improving the conductivity, cycle stability and reversibility of the positive electrode sheet, the high specific capacity of the positive electrode sheet can be taken into account.

[0068] In step S1, preparing the first slurry may include: adding a sulfur-selenium compound, a first conductive agent and a first binder into a first solvent, and uniformly mixing them to obtain the first slurry.

[0069] In the embodiments of the present application, there are no specific limitations on the types of the first conductive agent, the first binder, and the first solvent. Binder, conductive agent, and solvent types well-known to those skilled in the art and applicable to preparing the positive electrode slurry can be used. Exemplarily, the first conductive agent may include conductive carbon black. The first binder may include polyvinylidene fluoride. The first solvent may include N-methylpyrrolidone (NMP).

[0070] In some embodiments, the mass ratio of the sulfur-selenium compound, the first conductive agent, and the first binder may be (7-8):(1-2):1. Controlling the mass ratio of the sulfur-selenium compound, the first conductive agent, and the first binder within the above range can, while ensuring the mechanical strength and conductivity of the prepared positive electrode sheet, further improve the specific capacity of the prepared positive electrode sheet, and thus further improve the energy density of the battery.

[0071] In some embodiments, the chemical formula of the sulfur-selenium compound may be Se x S y , where x:y = 1:(2-10). In a specific embodiment, the sulfur-selenium compound may include SeS2. Because SeS2 has more excellent electrochemical performance and a more suitable sulfur-selenium ratio, it can better balance the conductivity, specific capacity, and cycling performance of the prepared positive electrode sheet.

[0072] The preparation of the second slurry in step S1 may include: adding the selenium-carbon composite material, the second conductive agent, and the second binder into the second solvent, and after mixing evenly, obtaining the second slurry.

[0073] In the embodiments of the present application, there are no specific limitations on the types of the second conductive agent, the second binder, and the second solvent. Binder, conductive agent, and solvent types well-known to those skilled in the art and applicable to preparing the positive electrode slurry can be used. Exemplarily, the second conductive agent may include conductive carbon black. The second binder may include polyvinylidene fluoride. The second solvent may include N-methylpyrrolidone. Of course, the type of the second conductive agent may be the same as or different from that of the first conductive agent. The types of the first binder and the second binder may be the same as or different from each other. The types of the first solvent and the second solvent may be the same as or different from each other.

[0074] In some embodiments, the mass ratio of the selenium-carbon composite material, the second conductive agent, and the second binder may be (7-8):(1-2):1. Controlling the mass ratio of the selenium-carbon composite material, the second conductive agent, and the second binder within the above range can, while ensuring the mechanical strength and conductivity of the prepared positive electrode sheet, further improve the cycling stability and reversibility of the prepared positive electrode sheet, and thus further improve the cycling life of the battery.

[0075] In some embodiments, please refer to Figure 3, the preparation method of the selenium-carbon composite material may include the following steps:

[0076] Step S11: Under a protective gas atmosphere, selenium and a carbon material are mixed and then subjected to ball milling treatment to obtain a mixture;

[0077] Step S12: After the mixture is compacted, under a protective gas atmosphere, the mixture is subjected to calcination treatment, and after cooling, a selenium-carbon composite material is obtained.

[0078] In the embodiments of the present application, first, selenium and the carbon material are uniformly mixed through ball milling treatment. Next, after the mixture is compacted, selenium and the carbon material are in full contact. Then, through calcination treatment, selenium can be melted into a liquid state and infiltrated into the pores of the carbon material. In this way, a large amount of selenium can be accommodated, and a selenium-carbon composite material with high quality can be prepared, thereby further improving the specific capacity of the finally prepared positive electrode sheet. The volume expansion of the selenium-based material during the battery cycle can also be better suppressed by the carbon material, and the shuttle effect of the intermediate discharge product can be better suppressed, thereby further improving the cycle stability and reversibility of the finally prepared positive electrode sheet.

[0079] In step S11, the mass ratio of selenium to the carbon material can be (7-8):(2-3), for example, it can be 8:2, 7:2, 8:3, 7:3 or any value between any two of the above numerical ranges. Controlling the mass ratio of selenium to the carbon material within the above range can enable more selenium to infiltrate into the pores of the carbon material, such as completely infiltrating selenium into the pores of the carbon material. In this way, it is beneficial to further improve the quality of the prepared selenium-carbon composite material, and then the finally prepared positive electrode sheet can better balance the specific capacity and the cycle stability and reversibility.

[0080] In some embodiments, the pore diameter of the carbon material can be 6nm to 13nm. In this way, while increasing the selenium loading amount, the shuttle effect of the intermediate discharge product can be effectively suppressed, thereby further improving the specific capacity and cycle performance of the positive electrode sheet.

[0081] Exemplarily, the carbon material may include at least one of carbon nanotubes, ordered mesoporous carbon, carbon fiber, graphene, and Ketjen black.

[0082] In step S11, the time of the ball milling treatment can be 22h to 26h, for example, it can be 22h, 23h, 24h, 25h, 26h or any value between any two of the above numerical ranges. In this way, the uniformity of the mixture of selenium and the carbon material can be better guaranteed, thereby improving the quality of the prepared selenium-carbon composite material, and then improving the performance of the finally prepared positive electrode sheet.

[0083] In step S12, the pressure for the compaction treatment can be 100 MPa to 120 MPa, the time for a single compaction treatment can be 20 min to 25 min; the number of compaction treatments can be 3 to 5 times. This can better ensure sufficient compaction between selenium and the carbon material, thereby improving the quality of the prepared selenium-carbon composite material, and further improving the performance of the finally prepared positive electrode sheet.

[0084] In step S12, the temperature for the calcination treatment can be 260 °C to 280 °C, and the time for the calcination treatment can be 20 h to 32 h. This can better ensure that selenium is fully heated and melted into a liquid state and infiltrates into the pores of the carbon material, thereby improving the quality of the prepared selenium-carbon composite material, and further improving the performance of the finally prepared positive electrode sheet.

[0085] The protective gas in step S12 can include inert gases, specifically, for example, at least one of argon, nitrogen, and helium.

[0086] The cooling step in step S12 can be carried out under a protective gas atmosphere, which can prevent selenium from being oxidized during the cooling process, and thus can better ensure the quality and performance of the prepared selenium-carbon composite material.

[0087] Of course, the method for preparing the selenium-carbon composite material given in the above embodiments is only an example, and this application does not exclude the case of using other methods to prepare the selenium-carbon composite material.

[0088] In some embodiments, in step S2, the step of coating the first slurry and the second slurry on at least one surface of the current collector may include: using a double-layer coating die head to simultaneously coat the first slurry and the second slurry on at least one surface of the current collector. This is convenient for controlling the coating amount and coating uniformity of each layer of slurry, can improve the coating quality, and can greatly improve the production efficiency and reduce the cost.

[0089] The type of the current collector in the embodiments of this application is not particularly limited, and a positive electrode current collector well-known to those skilled in the art can be used. Exemplarily, the current collector may include carbon-coated aluminum foil.

[0090] Of course, in the embodiments of this application, the case of using a single-layer coating die head to sequentially coat the first slurry and the second slurry on at least one surface of the current collector is not excluded. Specifically, for example, first, the first slurry is coated on at least one surface of the current collector and dried to form a first active material layer; next, the second slurry is coated on the first active material layer and dried to form a second active material layer.

[0091] The positive electrode sheet prepared in the above step S2 includes a current collector and a first active material layer and a second active material layer sequentially stacked on at least one surface of the current collector, wherein the first active material layer and the second active material layer correspond to the first slurry and the second slurry respectively.

[0092] In some specific embodiments, the thickness of the first active material layer can be 30 μm to 40 μm. For example, it can be 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm, or any value between any two of the above numerical ranges. In this way, the specific capacity and cycling performance of the positive electrode sheet can be better balanced.

[0093] In some specific embodiments, the thickness of the second active material layer can be 40 μm to 50 μm. For example, it can be 40 μm, 42 μm, 44 μm, 46 μm, 48 μm, 50 μm, or any value between any two of the above numerical ranges. In this way, while better improving the electrochemistry reaction kinetics of the positive electrode sheet and better suppressing the shuttle effect of intermediate discharge products, the cycling performance can be better balanced.

[0094] The embodiment of the present application also provides a lithium-selenium battery, which includes the positive electrode sheet described in any one of the above embodiments or a positive electrode sheet prepared by the preparation method of the positive electrode sheet described in any one of the above embodiments.

[0095] It should be understood that since the lithium-selenium battery in the embodiment of the present application includes the positive electrode sheet described in any one of the above embodiments or a positive electrode sheet prepared by the preparation method of the positive electrode sheet described in any one of the above embodiments, therefore, the beneficial effects of the positive electrode sheet in the above embodiments are all applicable to this lithium-selenium battery. The lithium-selenium battery in the embodiment of the present application has both a high energy density and a high cycling performance.

[0096] The technical solution of the present application will be further described below in conjunction with multiple embodiments and comparative examples.

[0097] Example 1

[0098] The preparation of the positive electrode sheet in this example includes the following steps:

[0099] Step S101: Selenium and multi-walled carbon nanotubes (carbon material) with an average pore diameter of 9.5 nm are placed in a ball mill together according to a mass ratio of 7:3. In an argon atmosphere, ball milling is carried out for 24 h to mix evenly to obtain a mixture; the mixture is subjected to a compaction treatment at 110 Mpa for a total of 4 times, and the compaction time for each time is 25 min. Then, in an argon atmosphere, the compacted mixture is calcined at a temperature of 275 °C for 24 h. After selenium is heated and melted into a liquid state, it penetrates into the pores of the carbon material. Next, it is cooled to room temperature in an argon atmosphere to obtain a selenium-carbon composite material;

[0100] Step S102: SeS2 (sulfur-selenium compound), conductive carbon black (first conductive agent), and polyvinylidene fluoride (first binder) are added to N-methylpyrrolidone (first solvent) according to a mass ratio of 7:2:1, and after mixing evenly, a first slurry is obtained;

[0101] Step S103: Add the selenium-carbon composite material, conductive carbon black (the second conductive agent), and polyvinylidene fluoride (the second binder) prepared in Step S101 into N-methylpyrrolidone (the second solvent) according to a mass ratio of 7:2:1. After mixing evenly, a second slurry is obtained.

[0102] Step S104: Using a double-layer coating die head, the first slurry prepared in Step S102 and the second slurry prepared in Step S103 are simultaneously coated on one side surface of the carbon-coated aluminum foil (current collector) by extrusion coating in such a way that the first slurry is closer to the current collector than the second slurry. After drying, a positive electrode plate is obtained. The positive electrode plate includes a current collector and a first active material layer and a second active material layer (corresponding to the first slurry and the second slurry respectively) stacked in sequence on one side surface of the current collector. Among them, the thickness of the first active material layer is 35 μm, and the thickness of the second active material layer is 45 μm.

[0103] Example 2

[0104] In this example, the preparation method of the positive electrode plate is basically the same as that in Example 1, except that:

[0105] (1) In Step S101, the average pore diameter of the multi-walled carbon nanotubes is 13 nm;

[0106] (2) In Step S101, the mass ratio of selenium to multi-walled carbon nanotubes is 8:2.

[0107] Example 3

[0108] In this example, the preparation method of the positive electrode plate is basically the same as that in Example 1, except that:

[0109] In the positive electrode plate prepared in Step S104, the thickness of the first active material layer is 30 μm.

[0110] Example 4

[0111] In this example, the preparation method of the positive electrode plate is basically the same as that in Example 1, except that:

[0112] In the positive electrode plate prepared in Step S104, the thickness of the second active material layer is 50 μm.

[0113] Comparative Example 1

[0114] The preparation of the positive electrode plate in this comparative example includes the following steps:

[0115] Step S201: Selenium and multi-walled carbon nanotubes with a pore size of 9.5 nm are placed together in a ball mill at a mass ratio of 7:3. In an argon atmosphere, ball milling is carried out for 24 h to mix evenly and obtain a mixture. The mixture is subjected to a compaction treatment at 110 Mpa, with a total of 4 compactions, and the compaction time for each time is 25 min. Then, in an argon atmosphere, the compacted mixture is calcined at a temperature of 275 °C for 24 h. After selenium is heated and melted into a liquid state, it penetrates into the pores of the carbon material. Next, it is cooled to room temperature in an argon atmosphere to obtain a selenium-carbon composite material;

[0116] Step S202: The selenium-carbon composite material, conductive carbon black, and polyvinylidene fluoride prepared in Step S201 are added to N-methylpyrrolidone at a mass ratio of 7:2:1. After mixing evenly, a positive electrode slurry is obtained;

[0117] Step S203: Using a double-layer coating die head, the positive electrode slurry prepared in Step S202 is coated on one side surface of a carbon-coated aluminum foil (current collector) by extrusion coating. After drying, a positive electrode sheet is obtained. The positive electrode sheet includes a current collector and a positive electrode active material layer on one side surface of the current collector. Among them, the thickness of the positive electrode active material layer is 80 μm.

[0118] Comparative Example 2

[0119] The preparation of the positive electrode sheet in this comparative example includes the following steps:

[0120] Step S301: SeS2, conductive carbon black, and polyvinylidene fluoride are added to N-methylpyrrolidone at a mass ratio of 7:2:1. After mixing evenly, a positive electrode slurry is obtained;

[0121] Step S302: Using a double-layer coating die head, the positive electrode slurry prepared in Step S301 is coated on one side surface of a carbon-coated aluminum foil (current collector) by extrusion coating. After drying, a positive electrode sheet is obtained. The positive electrode sheet includes a current collector and a positive electrode active material layer on one side surface of the current collector. Among them, the thickness of the positive electrode active material layer is 80 μm.

[0122] Comparative Example 3

[0123] The preparation of the positive electrode sheet in this comparative example includes the following steps:

[0124] Step S401: Selenium and multi-walled carbon nanotubes with a pore size of 9.5 nm are placed together in a ball mill at a mass ratio of 7:3. In an argon atmosphere, ball milling is carried out for 24 h to mix evenly and obtain a mixture. The mixture is subjected to a compaction treatment at 110 Mpa, with a total of 4 compactions, and the compaction time for each time is 25 min. Then, in an argon atmosphere, the compacted mixture is calcined at a temperature of 275 °C for 24 h. After selenium is heated and melted into a liquid state, it penetrates into the pores of the carbon material. Next, it is cooled to room temperature in an argon atmosphere to obtain a selenium-carbon composite material;

[0125] Step S402: Add SeS2, conductive carbon black, and polyvinylidene fluoride into N-methylpyrrolidone according to a mass ratio of 7:2:1. After mixing evenly, a first slurry is obtained.

[0126] Step S403: Add the selenium-carbon composite material prepared in Step S401, conductive carbon black, and polyvinylidene fluoride into N-methylpyrrolidone according to a mass ratio of 7:2:1. After mixing evenly, a second slurry is obtained.

[0127] Step S404: Using a double-layer coating die head, the first slurry prepared in Step S402 and the second slurry prepared in Step S403 are simultaneously coated on one side surface of the carbon-coated aluminum foil (current collector) by means of extrusion coating in such a way that the second slurry is closer to the current collector than the first slurry. After drying, a positive electrode plate is obtained. The positive electrode plate includes a current collector and a first active material layer and a second active material layer (corresponding to the second slurry and the first slurry respectively) stacked in sequence on one side surface of the current collector. Among them, the thickness of the first active material layer is 45 μm, and the thickness of the second active material layer is 35 μm. That is, the difference between the positive electrode plate prepared in Comparative Example 3 and the positive electrode plate prepared in Example 1 is that the positions of the first active material layer and the second active material in the positive electrode plate prepared in Example 1 are interchanged.

[0128] The positive electrode plates prepared in the above examples and each comparative example are made into batteries to test the electrochemical performance of the batteries.

[0129] The preparation steps of the battery are as follows: Cut the positive electrode plates prepared in the above examples and each comparative example into circular pieces with a diameter of 10 mm for standby; Use polypropylene (PP) as the separator; Use a metal lithium sheet with a diameter of 10 mm as the negative electrode plate; Use a solution of 1 mol / L LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (the volume ratio of EC and DEC is 1:1) as the electrolyte; After stacking the positive electrode plate, the separator, and the negative electrode plate in sequence, add the electrolyte and assemble a button cell.

[0130] Using a battery test system, the assembled button cell is subjected to electrochemical tests under the constant temperature condition of 25 °C. The specific tests are as follows:

[0131] (1) First Coulomb efficiency test: First, discharge at a constant current of 0.1C rate to 0V and stand for 5 minutes; Then continue to discharge at a constant current of 0.05C rate to 0V to obtain the first discharge capacity C1; After standing for 5 minutes, charge at a constant current of 0.1C rate to 2.0V to obtain the first charge capacity C2. The first Coulomb efficiency = (C2 / C1) × 100%.

[0132] (2) Specific capacity and capacity retention rate test after 100 cycles: First, discharge at a constant current of 0.2C to 0V and let it stand for 5 minutes; then charge at a constant current of 0.2C to 2.0V and let it stand for 5 minutes; then discharge at a constant current of 0.2C to 0V and let it stand for 5 minutes, and record the discharge capacity of the first cycle; repeat the above steps 100 times (i.e., 100 cycles), and record the discharge capacities of the first cycle and the 100th cycle (denoted as C0 and C 100 ), respectively). Specific capacity after 100 cycles = C 100 / mass of the positive active material, with the unit of mAh / g. Capacity retention rate after 100 cycles = (C 100 / C0) × 100%.

[0133] (3) Discharge specific capacity test at different rates: First, charge at a constant current of XC (XC = 0.1C, 0.33C, 0.5C or 1C) to 2.0V and let it stand for 5 minutes, then discharge at a constant current of XC to 0V, and record the discharge capacity at each rate. Discharge specific capacity at different rates = discharge capacity at XC rate / mass of the positive active material, with the unit of mAh / g.

[0134] The test results of the above tests are shown in Table 1.

[0135] Table 1

[0136]

[0137] As can be seen from the data in Table 1, the initial Coulombic efficiency of the batteries containing the positive electrode sheets prepared in Examples 1 to 4 and the capacity retention rate after 100 cycles are significantly improved compared with those of the batteries containing the positive electrode sheets prepared in Comparative Examples 2 and 3. Moreover, compared with Comparative Examples 1 to 3, the specific capacity of the batteries containing the positive electrode sheets prepared in Examples 1 to 4 is significantly improved after 100 cycles. That is, the positive electrode sheets prepared in Examples 1 to 4 have higher specific capacity, cycle reversibility and cycle life. In addition, compared with Comparative Example 1, the discharge specific capacity of the batteries containing the positive electrode sheets prepared in Examples 1 to 4 is higher at different discharge rates. In addition, compared with Comparative Examples 2 and 3, as the rate increases, the decrease in the discharge specific capacity of the batteries containing the positive electrode sheets prepared in Examples 1 to 4 is significantly smaller. That is, the positive electrode sheets prepared in Examples 1 to 4 not only have higher specific capacity, but also have higher rate performance and cycle stability. This shows that in the present application, by forming a first active material layer and a second active material layer stacked in sequence on the current collector, the first active material layer includes a sulfur-selenium compound, and through the combination of sulfur and selenium, the conductivity of the positive electrode sheet can be ensured and the specific capacity of the positive electrode sheet can be improved; the second active material layer includes a selenium-carbon composite material, and through the combination of selenium and the carbon material with a porous structure, the specific surface area of the positive electrode sheet can be significantly increased, thereby increasing the reaction active sites, promoting the infiltration of the electrolyte, and improving the electrochemistry reaction kinetics of the positive electrode sheet. Moreover, through the adsorption and confinement effects of the carbon material, the dissolution and shuttle of intermediate discharge products such as polyselenides and polysulfides into the electrolyte can be inhibited, thereby effectively inhibiting the shuttle effect, reducing the loss of the positive active material and side reactions on the negative electrode side. Thus, through the double-layer structure design of the first active material layer and the second active material layer, while improving the conductivity, cycle stability and reversibility of the positive electrode sheet, the high specific capacity of the positive electrode sheet can be taken into account, thereby effectively alleviating the capacity decay of the battery and effectively improving the cycle performance, rate performance and capacity performance of the battery.

[0138] In the positive electrode sheet prepared in Comparative Example 1, the positive electrode active material layer is a single-layer active material layer containing a selenium-carbon composite material. From the data in Table 1, it can be seen that although introducing carbon materials into selenium can inhibit the shuttle effect of intermediate discharge products, making the initial Coulombic efficiency of the battery containing the positive electrode sheet prepared in Comparative Example 1 and the capacity retention rate after 100 cycles at a relatively high level, and with the increase of the rate, the decrease amplitude of the discharge specific capacity of the corresponding battery is relatively small, that is, introducing carbon materials into selenium can inhibit the attenuation of the battery capacity. However, compared with Example 1, the specific capacity after 100 cycles and the discharge specific capacity at different rates of the battery containing the positive electrode sheet prepared in Comparative Example 1 are significantly reduced, that is, the introduction of carbon materials reduces the specific capacity of the positive electrode sheet, which in turn leads to a decrease in the energy density of the battery, that is, the comprehensive performance of the battery is poor.

[0139] In the positive electrode sheet prepared in Comparative Example 2, the positive electrode active material layer is a single-layer active material layer containing SeS2. From the data in Table 1, it can be seen that although SeS2 has a high theoretical capacity, making the discharge specific capacity of the battery containing the positive electrode sheet prepared in Comparative Example 2 relatively high at a rate of 0.1C, but with the increase of the cycle rate, the discharge specific capacity of the battery decreases rapidly, that is, the capacity of the battery decays rapidly, and the initial Coulombic efficiency, capacity retention rate after 100 cycles and specific capacity of the battery are significantly lower than those in Example 1. This shows that the lack of the positive electrode active material layer containing a selenium-carbon composite material on the surface layer cannot inhibit the shuttle effect of intermediate discharge products and the volume expansion of the positive electrode material during the cycling process, making the cycle stability and reversibility of the battery poor, that is, the comprehensive performance of the battery is also poor.

[0140] In the positive electrode sheet prepared in Comparative Example 3, although it contains two positive electrode active material layers similar to those in the positive electrode sheet prepared in Example 1, but since the active material layer containing the selenium-carbon composite material is located between the current collector and the active material layer containing SeS2, the carbon materials cannot effectively anchor the intermediate discharge products, that is, they cannot effectively inhibit the shuttle effect, and at the same time, they cannot effectively inhibit the volume expansion of the positive electrode material during the cycling process. From the data in Table 1, it can be seen that compared with Example 1, the capacity performance, cycle performance and rate performance of the battery containing the positive electrode sheet prepared in Comparative Example 1 are all poor. This shows that the positions of the first active material layer and the second active material layer in this application cannot be interchanged, otherwise the effective improvement of the battery performance cannot be achieved.

[0141] The present invention creatively proposes a novel double-layer cathode structure design, that is, a first active material layer and a second active material layer are sequentially stacked on at least one surface of the current collector. The second active material layer away from the current collector (which can be called the upper layer) includes a selenium-carbon composite material (Se@C), which improves the conductivity of the cathode sheet. The porous structure of the carbon material increases the specific surface area of the cathode sheet, increases the reaction active sites, and can promote the smooth progress of the electrochemical reaction kinetics. At the same time, the adsorption and confinement effects of the carbon material inhibit the shuttle effect of the intermediate discharge products, reduce the loss of the cathode active material, enhance the cycle stability and reversibility of the cathode sheet, and extend the cycle life of the battery. The first active material layer close to the current collector (which can be called the lower layer) includes a sulfur-selenium compound, which can increase the specific capacity of the cathode sheet, thereby effectively improving the mass and volume energy density of the battery, and overcoming the drawback that the energy density of the battery is reduced due to the introduction of the carbon material in the related technology. In this application, through the design of the double-layer structure, while taking into account the conductivity, cycle stability and reversibility of the selenium-based cathode sheet, the energy density is improved, thereby optimizing the comprehensive performance of the battery.

[0142] It should be noted that the cathode sheet embodiments, the preparation method embodiments of the cathode sheet and the lithium-selenium battery embodiments provided in this application belong to the same concept; among the technical features in the technical solutions recorded in each embodiment, they can be arbitrarily combined without conflict.

[0143] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners of this application. Without departing from the scope of the present disclosure, various deformations and changes can be made on the basis of the above embodiments. Similarly, the various technical features of the above embodiments can also be arbitrarily combined to form other embodiments of the present invention that may not be clearly described. Therefore, the above embodiments only represent several implementation manners of the present invention and do not limit the protection scope of the present invention patent.

Claims

1. A positive electrode sheet, characterized in that, It includes a current collector and a first active material layer and a second active material layer that are sequentially stacked on at least one surface of the current collector, and the first active material layer is disposed between the current collector and the second active material layer; The first active material layer includes a sulfur-selenium compound; The second active material layer includes a selenium-carbon composite material, and the carbon material in the selenium-carbon composite material has a porous structure, and selenium is distributed in the pores and / or on the surface of the carbon material.

2. The positive electrode sheet according to claim 1, characterized in that, The chemical formula of the sulfur-selenium compound is Se x S y , where x:y = 1:(2 - 10).

3. The positive electrode sheet according to claim 1, characterized in that, The selenium-carbon composite material satisfies at least one of the following characteristics: (1) The mass ratio of selenium to the carbon material is (7-8):(2-3); (2) The pore diameter of the carbon material is 6 nm to 13 nm; (3) The carbon material includes at least one of porous carbon nanotubes, porous carbon fibers, porous graphene, porous conductive carbon black, porous graphite, porous resin carbon, porous biomass carbon, and activated carbon.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The positive electrode sheet satisfies at least one of the following characteristics: (1) The thickness of the first active material layer is 30 μm to 40 μm; (2) The thickness of the second active material layer is 40 μm to 50 μm; (3) The first active material layer further includes a first conductive agent and a first binder, and the mass ratio of the sulfur-selenium compound, the first conductive agent, and the first binder is (7-8):(1-2):1; (4) The second active material layer further includes a second conductive agent and a second binder, and the mass ratio of the selenium-carbon composite material, the second conductive agent, and the second binder is (7-8):(1-2):

1.

5. A method for preparing a positive electrode sheet, characterized in that, The method includes the following steps: S1: Prepare a first slurry and a second slurry. The first slurry includes a sulfur-selenium compound, and the second slurry includes a selenium-carbon composite material. The carbon material in the selenium-carbon composite material has a porous structure, and selenium is distributed in the pores and / or on the surface of the carbon material; S2: Stack and coat the first slurry and the second slurry on at least one surface of the current collector in such a way that the first slurry is closer to the current collector than the second slurry, and after drying, the positive electrode sheet is obtained.

6. The method for preparing the positive electrode sheet according to claim 5, characterized in that, Preparing the first slurry includes: Add the sulfur-selenium compound, the first conductive agent, and the first binder into a first solvent. After mixing evenly, obtain the first slurry. Optionally, the mass ratio of the sulfur-selenium compound, the first conductive agent, and the first binder is (7-8):(1-2):

1. Optionally, the chemical formula of the sulfur-selenium compound is Se x S y , where x:y = 1:(2-10).

7. The manufacturing method of the positive electrode sheet according to claim 5, characterized in that, Preparing the second slurry includes: Adding the selenium-carbon composite material, a second conductive agent, and a second binder to a second solvent, and after mixing evenly, the second slurry is obtained; optionally, the mass ratio of the selenium-carbon composite material, the second conductive agent, and the second binder is (7-8):(1-2):

1.

8. The method for preparing the positive electrode sheet according to any one of claims 5 to 7, characterized in that, The preparation method of the selenium-carbon composite material includes: Under a protective gas atmosphere, mixing selenium and a carbon material and then performing ball milling treatment to obtain a mixture; After compacting the mixture, under a protective gas atmosphere, performing calcination treatment on the mixture, and after cooling, the selenium-carbon composite material is obtained.

9. The method for preparing the positive electrode sheet according to claim 8, wherein, The method satisfies at least one of the following characteristics: (1) The mass ratio of selenium to the carbon material is (7-8):(2-3); (2) The pore diameter of the carbon material is 6 nm to 13 nm; (3) The carbon material includes at least one of carbon nanotubes, ordered mesoporous carbon, carbon fibers, graphene, and Ketjen black; (4) The time of the ball milling treatment is 22 h to 26 h; (5) The pressure for compaction is 100 MPa to 120 MPa, the time for single compaction is 20 min to 25 min; the number of compaction times is 3 to 5 times; (6) The temperature for calcination treatment is 260 °C to 280 °C, and the time for calcination treatment is 20 h to 32 h.

10. A lithium-selenium battery, characterized in that, The positive electrode sheet according to any one of claims 1 to 4, or the positive electrode sheet prepared by the preparation method of the positive electrode sheet according to any one of claims 5 to 9.

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