Positive pole piece, preparation method thereof and secondary battery

Abstract

The invention relates to a positive pole piece, a preparation method thereof and a secondary battery, and belongs to the technical field of battery preparation. The positive pole piece comprises a positive pole current collector and a positive pole diaphragm attached to the surface of the positive pole current collector, and the positive pole diaphragm comprises a network-shaped structure formed by fibers of a fiberized binder, a positive pole active material dispersed in the network-shaped structure and an ionic conductor material. The ion conductor material is provided with at least one ion transmission channel; and the ion transmission channel is arranged along the thickness direction of the positive electrode membrane in an oriented manner. Wherein the ionic conductivity of the ionic conductor material is not lower than 0.02 S / cm, and the thickness range of the positive electrode membrane is 30-2000 microns. The ion conductor material with the ion transmission channel is introduced into the positive electrode diaphragm, and the orientation of the ion transmission channel is controlled, so that the ion transmission performance of the dry-method thick positive electrode plate can be effectively improved, the specific capacity of the positive electrode active material is improved, and the rate charge-discharge performance and the first effect of the battery are further improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a positive electrode sheet, a method for preparing the same, and a secondary battery. Background Technology

[0002] Because wet processing is prone to cracking and delamination during drying, dry processing is currently the most common method for preparing thick positive electrode sheets. The dry process for preparing thick positive electrode sheets typically involves: mixing the positive active material with binders, conductive agents, and other raw materials, followed by fiberization, then hot-rolling to form a positive electrode film, and finally laminating the positive electrode film onto a positive current collector to obtain the positive electrode sheet. However, due to the absence of solvents, uneven mixing of the positive active material, binders, and conductive agents during raw material mixing and fiberization can easily occur, leading to uneven fiberization of the binder. Furthermore, the greater thickness of the positive electrode sheet results in longer ion transport paths and slower conduction, thus limiting the specific capacity of the positive active material. Consequently, the battery's rate charge / discharge performance and initial charge / discharge efficiency (hereinafter referred to as first-time efficiency) need improvement. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a positive electrode sheet, its preparation method, and a secondary battery, in order to improve the ion transport performance of existing positive electrode sheets, thereby enhancing the specific capacity of positive electrode active materials and improving the rate charge / discharge performance and first-cycle efficiency of the battery.

[0004] In a first aspect, embodiments of this application provide a positive electrode sheet, comprising a positive current collector and a positive electrode membrane attached to at least one side surface of the positive current collector. The positive electrode membrane comprises a network structure formed by fibrous filaments of a fibrous binder, a positive active material and an ion conductor material dispersed in the network structure, the ion conductor material having at least one ion transport channel and the ion transport channel being oriented along the thickness direction of the positive electrode membrane; wherein, the ion conductivity of the ion conductor material is not less than 0.02 S / cm; the thickness of the positive electrode membrane ranges from 30 μm to 2000 μm. In the above technical solution, this application introduces an ion conductor material with high ion conductivity into the positive electrode film. After the ion conductor material is mixed with the positive electrode active material and the fibrous binder, it is uniformly dispersed in the network structure formed by the fibrous binder, which can effectively improve the ion transport efficiency of the electrode. By setting ion transport channels in the ion conductor material and controlling the orientation and arrangement of the ion transport channels along the thickness direction of the positive electrode film, the problem of long ion transport paths and slow conduction in dry-process thick positive electrode films can be effectively solved. At the same time, the influence of hot pressing during the preparation of the positive electrode film can be reduced, avoiding the limitation of the ion conduction performance of the ion conductor material itself. This allows ions inside the positive electrode film to be effectively transported to the positive electrode current collector, thereby effectively improving the specific capacity of the positive electrode active material and improving the rate charge / discharge performance and first-time efficiency of the battery.

[0005] In some embodiments, the ion conductor material includes at least one first ion transport channel and a plurality of second ion transport channels, the first ion transport channels being oriented along the thickness direction of the positive electrode film, and the second ion transport channels being connected to the first ion transport channels.

[0006] In the above technical solution, by setting a first ion transport channel oriented along the thickness direction of the positive electrode film in the ion conductor material, and multiple divergent second ion transport channels connected to the first ion transport channel, it is beneficial for ions from all sides to be transported to the first ion transport channel through the second ion transport channels, thereby facilitating the rapid transport of ions at various positions inside the electrode, further shortening the ion transport path and improving the ion transport efficiency.

[0007] In some embodiments, multiple ion conductor materials are sequentially overlapped along the thickness direction of the positive electrode film, and the ion transport channels of the multiple ion conductor materials are sequentially connected.

[0008] In the above technical solution, by controlling the ion conductor material to form a three-dimensional overlap along the thickness direction, it is beneficial to further shorten the ion transport path, facilitate rapid ion transport inside the positive electrode film, and thus improve the ion transport efficiency.

[0009] In some embodiments, at least a portion of the fibers are adhered to the surface of the positive electrode active material, and the fibers are coated with an ion-conducting material.

[0010] In the above technical solution, by using fiber filaments to attach a portion of the ion-conducting material to the surface of the positive electrode active material, it is beneficial to further shorten the ion transport path, increase the ion transport rate, and thus improve the specific capacity of the positive electrode active material, thereby enhancing the battery's rate charge-discharge performance. Furthermore, using fiber filaments for adhesion and fixation helps improve the structural stability and interfacial bonding between the ion-conducting material and the positive electrode active material, thereby improving the battery's cycle stability.

[0011] In some embodiments, any 2μm × 2μm region in the longitudinal section of the positive electrode membrane contains ion-conducting material. In the above technical solution, the presence of ion-conducting material in any 2μm × 2μm region in the longitudinal section of the positive electrode membrane indicates that the ion-conducting material is uniformly distributed within the positive electrode membrane. Part of it coats the surface of the positive electrode active material, part adheres to the binder fibers, and another part is freely distributed within the positive electrode membrane. This facilitates the construction of a highly efficient and continuous ion transport network within the positive electrode membrane, further improving the ion transport effect.

[0012] In some embodiments, the ion conductor material includes at least one of boron nitride nanosheets, graphene, oxide solid electrolyte, sulfide solid electrolyte, or nanowires.

[0013] In the above technical solutions, all of these ion conductor materials have high ion conductivity. By setting up ion transport channels, they can exert excellent ion transport effects in the dry preparation of thick positive electrode sheets.

[0014] In some embodiments, the ion conductor material includes boron nitride nanosheets, at least one ion transport channel extending along the planar direction of the boron nitride nanosheets, the planar direction of the boron nitride nanosheets being oriented in the thickness direction of the positive electrode film.

[0015] In the above technical solution, boron nitride nanosheets are selected as the ion conductor material. Boron nitride nanosheets possess high ionic conductivity, with the ionic conductivity of boron nitride nanosheets with ion transport channels reaching up to 0.3 S / cm. Furthermore, by arranging the ion transport channels along a planar direction, and considering the anisotropy of the boron nitride nanosheets, the planar orientation of the boron nitride nanosheets can be controlled by applying a magnetic field to align them along the thickness direction of the positive electrode film, thus achieving the alignment of the ion transport channels along the thickness direction of the positive electrode film.

[0016] In some embodiments, the average diameter of the boron nitride nanosheets is 1 nm to 10 μm.

[0017] In the above technical solution, by controlling the average diameter of boron nitride nanosheets within a wide range, it is beneficial to achieve uniform dispersion in the positive electrode film. Simultaneously, the boron nitride nanosheets can overlap to form an ion transport network, further improving the ion transport performance of the positive electrode. When the average diameter of the boron nitride nanosheets is small (e.g., 1 nm to 600 nm), they can tightly wrap around the surface of the positive electrode active material, reducing film resistance and improving the first charge-discharge efficiency (hereinafter referred to as first efficiency). Furthermore, the smaller diameter of the boron nitride nanosheets facilitates uniform dispersion and overlap within the positive electrode film, forming a three-dimensional ion transport network along the thickness direction of the positive electrode film. It also facilitates adhesion to fibers, further shortening the ion transport distance and improving the ion transport effect. When the average diameter of the boron nitride nanosheets is large (e.g., 1 μm to 5 μm), it helps to shorten the ion transport path, which is more conducive to rapid ion transport. By simultaneously introducing nano- and micro-sized boron nitride nanosheets into the positive electrode film, the boron nitride nanosheets of different sizes can be uniformly dispersed inside the electrode to construct an efficient and continuous ion transport network, thereby further improving the specific capacity of the positive electrode active material and enhancing the rate charge and discharge performance and first-time efficiency of the battery. In some implementations, the mass percentage of the ion conductor material is 0.2 wt% to 10 wt% based on the total mass of the positive electrode film.

[0018] In the above technical solution, by controlling the mass ratio of ion conductor material within a suitable range, it is beneficial for the ion conductor material to be uniformly dispersed in the positive electrode film, further improving the ion transport performance of the electrode, enhancing the structural stability of the electrode, improving the interfacial performance between the electrode and the electrolyte, and thus improving the cycle performance of the battery.

[0019] In some embodiments, the fiber filaments of the fibrous binder have an average diameter of 10 nm to 100 nm, an average length of 1 μm to 100 μm, and an average aspect ratio of 10 to 10000.

[0020] In the aforementioned technical solution, controlling the fiber filaments of the fibrous binder to have a smaller diameter and a larger length, i.e., a larger aspect ratio, is beneficial for improving the mechanical strength and toughness of the electrode sheet. It also allows for the formation of a more stable network structure within the positive electrode film, enhancing the bonding force between positive electrode active material particles and between the positive electrode active material and the ion conductor material. This, in turn, improves the structural stability of the electrode sheet and enhances the cycle stability of the battery. Furthermore, the larger aspect ratio of the fiber filaments facilitates the formation of three-dimensional overlaps between ion conductor materials and between positive electrode active materials, thereby further shortening the ion transport path and improving the ion transport performance of the electrode sheet.

[0021] In some embodiments, the positive electrode film also includes a conductive agent; the conductive agent accounts for 0.2wt% to 5wt% of the total mass of the positive electrode film.

[0022] In the above technical solution, by controlling the mass ratio of the conductive agent within a suitable range, it is beneficial to form a good conductive network while avoiding a reduction in the content of the positive electrode active material. This can further improve the specific capacity of the positive electrode active material, thereby enhancing the battery's rate charge / discharge performance and first-time efficiency. Furthermore, the conductive agent can be effectively connected to the positive electrode active material through fibers and three-dimensionally overlapped with the ion-conducting material, thus forming a dual electron and ion transport network and reducing the electrode resistivity.

[0023] Secondly, embodiments of this application also provide a method for preparing the positive electrode sheet provided in the first aspect of this application, comprising the following steps: A fiberizable binder, a positive electrode active material, and an ion conductor material are mixed, and the binder is fiberized to form filaments to obtain a mixed powder. A magnetic field is applied to the mixed powder to orient it, followed by hot pressing to form a positive electrode film; wherein, under the action of the magnetic field, at least one ion transport channel of the ion conductor material is oriented and arranged along the thickness direction of the positive electrode film; the fiber filaments overlap each other to form a network structure during hot pressing. A positive electrode sheet is obtained by combining a positive electrode membrane and a positive electrode current collector.

[0024] In the above technical solution, the positive electrode sheet is prepared using a dry process, and an ion conductor material with ion transport channels is introduced into the mixed powder. The ion conductor material and the positive electrode active material are uniformly dispersed in the positive electrode film, and after fiberization, they are uniformly dispersed in the network structure formed by the fiberization of the binder, which is beneficial to improving the ion transport performance of the electrode sheet. By applying a magnetic field to orient the ion transport channels, the ion transport path can be further shortened, and the ion transport efficiency can be improved. Furthermore, due to the presence of ion transport channels, the influence of hot pressing during the preparation of the positive electrode film can be reduced, avoiding the limitation of the ion conduction performance of the ion conductor material itself. This allows ions inside the positive electrode film to be effectively transported to the positive electrode current collector, thereby effectively solving the problem of long ion transport paths and slow conduction in dry-process thick positive electrode sheets, and thus effectively improving the specific capacity of the positive electrode active material, improving the rate charge and discharge performance and first-time efficiency of the battery.

[0025] In some embodiments, the ion conductor material includes boron nitride nanosheets, at least one ion transport channel extending along the planar direction of the boron nitride nanosheets; the method of orienteding the mixed powder by applying a magnetic field includes: applying a magnetic field to the mixed powder such that the planar positive electrode film of the boron nitride nanosheets is oriented in the thickness direction.

[0026] In the above technical solution, by designing ion transport channels extending along the planar direction in boron nitride nanosheets, and given the anisotropy of the boron nitride nanosheets themselves, a magnetic field can be applied to align the planar boron nitride nanosheets with the thickness direction of the positive electrode film, thereby achieving the alignment of the ion transport channels along the thickness direction of the positive electrode film. This method is simple and efficient, eliminating the need for magnetic treatment of the boron nitride nanosheets. Furthermore, due to the excellent ion conduction and thermal conductivity of the boron nitride nanosheets in the planar direction, the ion transport performance of the positive electrode can be further improved, thereby enhancing the specific capacity of the positive electrode active material and improving the battery's rate charge / discharge performance, initial efficiency, and safety.

[0027] In some embodiments, the method for preparing the mixed powder includes: mixing a binder and an ion conductor material, and applying a magnetic field to orient at least one ion transport channel of the ion conductor material along a predetermined direction to obtain a first powder; mixing the first powder, a positive electrode active material, and a conductive agent, and causing the binder to fiberize to form filaments.

[0028] In the above technical solution, by first mixing the binder and the ion conductor material and orienting the ion transport channels, the ion conductor material can be uniformly dispersed in the network structure formed by the fiberized binder and at least partially attached to the fiber filaments after fiberization. After further mixing with the positive electrode active material and conductive agent, the ion conductor material and conductive agent can uniformly adhere to the surface of the positive electrode active material, forming a stable and uniform ion and electron transport network around the positive electrode active material. This facilitates rapid ion transport, thereby further improving the specific capacity of the positive electrode active material and enhancing the battery's rate charge / discharge performance.

[0029] In some embodiments, the mixing of the binder and the ionic conductor material includes continuously adding the ionic conductor material to the binder under stirring conditions.

[0030] In the above technical solution, the binder and ion conductor material are mixed by continuous addition rather than one-time addition, which is conducive to the uniform mixing and dispersion of the two. Subsequently, it is beneficial for the ion conductor material to be uniformly dispersed in the network structure formed by the fibrous binder, thereby further improving the ion transport performance of the electrode.

[0031] In some embodiments, the fiberization step includes: mixing a first powder, a positive electrode active material, and a conductive agent at a low speed under low temperature conditions to obtain a second powder; heating the second powder while mixing at a low speed to perform pre-fiberization, and keeping it at that temperature for a period of time; and mixing the second powder at a high speed to complete the fiberization.

[0032] In the above technical solution, the stepwise mixing and pre-fiberization steps facilitate the full fiberization of the binder and ensure uniform mixing of all components. This improves the structural stability of the electrode, further promotes ion and electron transport, and consequently enhances the battery's rate charge / discharge efficiency and cycle performance. Furthermore, the uniform mixing of the first powder, positive electrode active material, and conductive agent helps to further form a highly efficient and continuous ion and electron transport network within the electrode, further improving the specific capacity of the positive electrode active material and further enhancing the battery's rate charge / discharge performance and initial efficiency.

[0033] Thirdly, embodiments of this application also provide a secondary battery, including the positive electrode sheet described in the first aspect or the positive electrode sheet prepared by the preparation method of the second aspect.

[0034] In the above technical solution, because the positive electrode has high ionic conductivity, the secondary battery has high specific capacity, as well as high rate charge / discharge performance and first-time efficiency. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the ion transport channel in the boron nitride nanosheet provided in the embodiments of this application.

[0037] Figure 2 This is a schematic diagram of the three-dimensional overlapping structure of boron nitride nanosheets in the positive electrode film provided in the embodiments of this application.

[0038] Figure 3 This is a process flow diagram of a method for preparing a positive electrode sheet provided in an embodiment of this application.

[0039] Figure 4 This is a scanning electron microscope (SEM) image of the positive electrode sheet provided in Embodiment 1 of this application.

[0040] Figure 5 This is an EDS cross-sectional view of the N element in the positive electrode film provided in Embodiment 1 of this application.

[0041] Figure 6 for Figure 5 A magnified view of a portion of the image.

[0042] Figure 7 The first charge-discharge curves of the batteries in Examples 1-5 and Comparative Examples 1-3 at a 1C rate are shown.

[0043] Explanation of reference numerals in the attached figures: 100 - Boron nitride nanosheets; 10 - First ion transport channel; 20 - Second ion transport channel; P - Length direction; 200 - Positive electrode film; T - Thickness direction. Detailed Implementation

[0044] The following detailed description, with appropriate reference to the accompanying drawings, discloses the positive electrode sheet, the method for preparing the positive electrode sheet, and embodiments of a secondary battery including the positive electrode sheet. 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0045] 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 also 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 "a~b" 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.

[0046] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0047] Because wet processing is prone to cracking and delamination during drying, dry processing is currently the most common method for preparing thick positive electrode sheets. The dry process for preparing thick electrodes typically involves: mixing the positive active material with binders, conductive agents, and other raw materials, followed by fiberization, then hot-rolling to form a positive electrode film, and finally bonding the positive electrode film to a current collector to obtain the electrode sheet. However, the absence of a solvent in this process can lead to uneven mixing of the positive active material, binders, and conductive agents, insufficient fiberization of the binder, and the large thickness of the positive electrode film results in long ion transport paths and slow conduction. In particular, ions inside the positive electrode film cannot be effectively transported to the surface, thus limiting the specific capacity of the electrode active material and requiring improvement in the battery's rate charge / discharge performance and initial efficiency.

[0048] Although existing research has disclosed the introduction of oxide solid electrolytes into the positive electrode film during the dry process preparation of thick positive electrode sheets, the oxide solid electrolytes contain some channels and pores that can be used for ion transport. However, these pores and channels are irregular and disordered, and after dry compaction, it is difficult to effectively improve the ion transport performance of the electrode sheet in the thick electrode sheet.

[0049] Based on this, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive electrode membrane attached to at least one surface of the positive current collector. The positive electrode membrane includes a network structure formed by fibers of a fibrous binder, a positive active material and an ion conductor material dispersed in the network structure, the ion conductor material having at least one ion transport channel and the ion transport channels being oriented along the thickness direction of the positive electrode membrane. The ion conductivity of the ion conductor material is not less than 0.02 S / cm; the thickness of the positive electrode membrane ranges from 30 μm to 2000 μm.

[0050] In this application embodiment, "ionic conductor material" refers to a class of materials capable of transporting ions, such as boron nitride nanosheets and oxide solid electrolytes. "Ionic conductivity" refers to the current conduction capability generated by the directional movement of ions in a substance under the action of an electric field under certain conditions, and is used to measure the ionic conduction capability of ionic conductor materials.

[0051] It should be understood that the ionic conductivity of the ionic conductor material in the embodiments of this application is an average value obtained by testing a certain mass of ionic conductor material powder. Therefore, under the same mass of powder, the average size of the ionic conductor material varies greatly due to the influence of the number and distribution uniformity of individual ionic conductor materials, and the ionic conductivity obtained by testing may be the same.

[0052] In this embodiment, "ion transport channel" refers to a specific structure or space within or on the surface of an ion-conducting material that provides a transport path for ions. "Ion transport channels are oriented along the thickness direction of the positive electrode film" means that the length direction or extension direction of the ion transport channels in the ion-conducting material is oriented along the thickness direction of the positive electrode film, wherein the angle between the length direction or extension direction of the ion transport channels and the thickness direction of the positive electrode film is within 30°. Further, the length direction or extension direction of the ion transport channels is parallel to the thickness direction of the positive electrode film.

[0053] When the ion conductor material is a two-dimensional sheet material (such as boron nitride nanosheets), the ion transport channels extend along the plane of the two-dimensional sheet material. In this case, by controlling the orientation of the two-dimensional sheet material along the thickness direction of the positive electrode film, the ion transport channels can be oriented along the thickness direction of the positive electrode film. Understandably, the ion conductor material can contain multiple ion transport channels, as long as at least one ion transport channel can be oriented.

[0054] Understandably, by designing ion transport channels in ion-conducting materials, the ionic conductivity of these materials can be effectively improved. In the embodiments of this application, the ionic conductivity of the ion-conducting material is not less than 0.02 S / cm, for example, 0.02 S / cm, 0.03 S / cm, 0.1 S / cm, 0.2 S / cm, 0.3 S / cm, 0.4 S / cm, 2 S / cm and above. Further, the ionic conductivity of the ion-conducting material is between 0.02 S / cm and 2 S / cm.

[0055] When the thickness of the positive electrode sheet is not less than 70 μm, it can be considered a thick electrode sheet. In the embodiments of this application, the thickness range of the positive electrode film is 30 μm to 2000 μm, indicating that the positive electrode sheet of the embodiments of this application can be a conventional thickness electrode sheet, especially suitable for thick electrode sheets. Further, the thickness range of the positive electrode film is 70 μm to 1000 μm. As an example, the thickness of the positive electrode sheet can be 30 μm, 50 μm, 70 μm, 100 μm, 150 μm, 500 μm, 1000 μm, 2000 μm, or any value or range between two of these.

[0056] This application introduces an ion-conducting material with high ion conductivity into the positive electrode film. After mixing with the positive electrode active material and a fibrous binder, the ion-conducting material is uniformly dispersed within a fibrous network structure formed by the fibrous binder, effectively improving ion transport efficiency. By establishing ion transport channels within the ion-conducting material and controlling their orientation along the thickness direction of the positive electrode film, the ion transport path can be shortened, further improving ion transport efficiency. This effectively solves the problems of long ion transport paths and slow conduction in dry-process thick positive electrode sheets. Simultaneously, the presence of ion transport channels reduces the impact of hot-pressing during the positive electrode film fabrication process, avoiding limitations on the ion-conducting properties of the ion-conducting material itself. This allows ions inside the positive electrode film to be efficiently transported to the positive electrode current collector and / or the surface of the positive electrode sheet, thereby effectively improving the specific capacity of the positive electrode active material and enhancing the battery's rate charge / discharge performance and initial efficiency.

[0057] In some embodiments, the ion conductor material includes at least one first ion transport channel and a plurality of second ion transport channels, wherein the first ion transport channels are oriented along the thickness direction of the positive electrode film, and the second ion transport channels are connected to the first ion transport channels.

[0058] Understandably, the first ion transport channel serves as the main channel, and multiple second ion transport channels serve as sub-channels. The first ion transport channel extends along the thickness direction of the positive electrode film, while one end of the second ion transport channel is connected to the first ion transport channel, and the other end radiates outwards, forming a network structure. This facilitates the collection of ions from various locations inside the positive electrode film through the second ion transport channel into the first ion transport channel, and their rapid transport to the electrode surface.

[0059] In some embodiments, multiple ion conductor materials are sequentially overlapped along the thickness direction of the positive electrode film, and the ion transport channels of the multiple ion conductor materials are sequentially connected.

[0060] Taking boron nitride nanosheets as an example of ion conductor materials, Figure 1 This is a schematic diagram of the ion transport channel in the boron nitride nanosheet provided in the embodiments of this application. Figure 2 This is a schematic diagram illustrating the three-dimensional overlapping structure of boron nitride nanosheets in a positive electrode film, as provided in an embodiment of this application. Please refer to... Figure 1 The boron nitride nanosheet 100 has a first ion transport channel 10 and multiple second ion transport channels 20 in its planar direction. The first ion transport channel 10 extends along the length direction P, and the multiple second ion transport channels 20 connect to the first ion transport channel 10 and diverge in all directions. See also... Figure 2 Multiple boron nitride nanosheets 100 are sequentially overlapped along the thickness direction T of the positive electrode film 200, and the first ion transport channels 10 are sequentially connected.

[0061] In some embodiments, at least a portion of the fibers are adhered to the surface of the positive electrode active material, and the fibers are coated with an ion conductor material.

[0062] In some embodiments, any 2μm×2μm region in the longitudinal section of the positive electrode film contains ion-conducting material.

[0063] In this application, "any 2μm × 2μm region in the longitudinal section of the positive electrode membrane contains ion-conducting material" means that when the longitudinal section of the positive electrode membrane is tested, the ion-conducting material is uniformly dispersed in the positive electrode membrane. Therefore, any selected 2μm × 2μm region contains ion-conducting material. Furthermore, any 1μm × 1μm region in the longitudinal section of the positive electrode membrane contains ion-conducting material. In some embodiments, the mass percentage of the ion conductor material is 0.2 wt% to 10 wt% based on the total mass of the positive electrode membrane. As an example, the mass percentage of the ion conductor material is 0.2 wt%, 0.5 wt%, 1 wt%, 2 wt%, 5 wt%, 10 wt% or any combination of two of the above values ​​based on the total mass of the positive electrode membrane.

[0064] In the embodiments of this application, "fibrillated adhesive" refers to an adhesive that has been fiberized under high shear force, including a number of fiber filaments, which can form a network structure.

[0065] In some embodiments, the fibrous binder accounts for 2 wt% to 5 wt% of the total mass of the positive electrode membrane. As an example, the fibrous binder accounts for 2 wt%, 3 wt%, 4 wt%, 5 wt% of the total mass of the positive electrode membrane, or any range between two of these values.

[0066] In some embodiments, the positive electrode film further includes a conductive agent, wherein the mass percentage of the conductive agent is 0.2 wt% to 5 wt% based on the total mass of the positive electrode film. As an example, the mass percentage of the conductive agent is 0.2 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%, or any combination of two of the above values.

[0067] This application does not specifically limit the selection of positive electrode active materials. As an example, positive electrode active materials may include at least one of the following: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0068] In some embodiments, the mass percentage of the positive electrode active material is 80wt% to 96wt% based on the total mass of the positive electrode film. As an example, the mass percentage of the positive electrode active material is 80wt%, 85wt%, 87wt%, 90wt%, 92wt%, 96wt%, or any range of two of the above values ​​based on the total mass of the positive electrode film.

[0069] The structure and performance of the positive electrode sheet are described in detail below, taking into account the preparation method of the positive electrode sheet.

[0070] Figure 3 For a process flow diagram of a method for preparing a positive electrode sheet provided in this application embodiment, please refer to [link / reference]. Figure 3 The preparation method of the positive electrode sheet includes the following steps: S10: Mix a fiberizable binder, a positive electrode active material, and an ion conductor material, and fiberize the binder to form filaments to obtain a mixed powder.

[0071] In some embodiments, the ion conductor material includes at least one of boron nitride nanosheets, graphene, oxide solid electrolytes or sulfide solid electrolytes or nanowires. The nanowires may be lithium nitride nanowires or Li-HA-F nanofibers, etc.

[0072] These ion-conducting materials with ion transport channels can be purchased commercially or obtained through special processing or preparation of conventional ion-conducting materials. For example, oriented ion transport channels can be formed on the surface of boron nitride nanosheets using transition metal nanoparticle etching; oxide solid electrolytes or sulfide solid electrolytes with oriented ion transport channels can be prepared using nanotemplating methods.

[0073] Furthermore, the ion conductor material includes boron nitride nanosheets, at least one ion transport channel extending along the planar direction of the boron nitride nanosheets, the planar direction of the boron nitride nanosheets being oriented in the thickness direction of the positive electrode film.

[0074] Understandably, boron nitride nanosheets, as two-dimensional sheet materials, have mutually perpendicular thickness and planar directions. The planar direction exhibits significantly stronger ion-conductivity and thermal conductivity than the corresponding properties in the thickness direction. The planar direction can be the length direction, the width direction, or any other direction between the length and width directions, as long as it is perpendicular to the thickness direction. Preferably, the planar direction of the boron nitride nanosheets is considered to be the length direction.

[0075] In some embodiments, the average diameter of the boron nitride nanosheets is 10 nm to 10 μm, and the average thickness is 10 nm to 300 nm. As an example, the average diameter of the boron nitride nanosheets is 10 nm, 50 nm, 100 nm, 1 μm, 2 μm, 5 μm, 10 μm, or any combination of two of the above values; the average thickness is 10 nm, 50 nm, 100 nm, 300 nm, or any combination of two of the above values.

[0076] In this embodiment, the average diameter of the boron nitride nanosheets has a meaning known in the art and can be obtained using conventional testing methods and equipment. For example, images of the boron nitride nanosheets can be captured using a transmission electron microscope (TEM), and the diameter can be obtained by measuring the images using image analysis software. After 100 measurements, the average diameter of the boron nitride nanosheets can be calculated.

[0077] In some embodiments, the average diameter of the boron nitride nanosheets is 10 nm to 600 nm. As an example, the average diameter of the boron nitride nanosheets is 10 nm, 50 nm, 100 nm, 200 nm, 400 nm, 600 nm, or any combination of two of these values. When the average diameter of the boron nitride nanosheets is small (in the nanometer range), it is beneficial for them to adhere tightly to the surface of the positive electrode active material and the surface of the fiber filaments, and for them to be uniformly dispersed in the positive electrode film, thereby improving the ion transport effect inside the positive electrode film. Furthermore, the smaller the average diameter of the boron nitride nanosheets, the lower the film resistance, the greater the peel strength, and the better the initial efficiency of the battery.

[0078] In some embodiments, the average diameter of the boron nitride nanosheets is 1 μm to 5 μm. When the average diameter of the boron nitride nanosheets is larger, on the order of micrometers, it is beneficial to shorten the ion transport path.

[0079] In some embodiments, the ion conductor material includes boron nitride nanosheets with average sheet diameters of both nanometer (e.g., 10 nm to 600 nm) and micrometer (1 μm to 5 μm). The simultaneous use of nanometer- and micrometer-sized boron nitride nanosheets allows them to overlap and form three-dimensional ion transport channels, which helps to shorten the ion transport path and improve ion transport efficiency. Furthermore, it can further enhance the film-forming properties of the positive electrode film.

[0080] Furthermore, in the mixed powder, the mass ratio of nanoscale boron nitride nanosheets to microscale boron nitride nanosheets can be (1~5):(1~5), for example, any combination of 1:1, 2:1, 3:1, 4:1, 5:1, 1:2, 1:3, etc.

[0081] In this embodiment, the boron nitride nanosheets with ion transport channels can be obtained commercially or by self-production.

[0082] Exemplarily, a method for forming ion transport channels on boron nitride nanosheets includes: (1) Apply transition metal nanoparticles to the surface of boron nitride nanosheets.

[0083] (2) Under heating and reducing gas environment, the transition metal nanoparticles react with boron nitride nanosheets, and the direction of the reducing gas flow is controlled along the plane of the boron nitride nanosheets. Under the push of the gas flow, ion transport channels are etched along the plane of the boron nitride nanosheets.

[0084] (3) Remove the transition metal nanoparticles remaining on the surface of the boron nitride nanosheets.

[0085] By heating and operating in a reducing gas environment, transition metal nanoparticles catalyze the decomposition of the reducing gas to form reducing atoms. These reducing atoms attached to the transition metal nanoparticles further react with boron (B) and nitrogen (N) atoms on the boron nitride nanosheets, causing the BN bonds to break and resulting in etching. Furthermore, by controlling the airflow to direct the movement of the transition metal nanoparticles, ion transport channels with specific orientations can be formed on the surface of the boron nitride nanosheets.

[0086] Understandably, by controlling the ion transport channels formed in a specific direction during the airflow propulsion process, preferably extending along the length of the boron nitride nanosheets, the ion transport channels can be oriented and arranged along the thickness direction of the positive electrode film by subsequently applying a magnetic field. However, during the actual airflow propulsion process, it is inevitable that a large number of transition metal nanoparticles will disperse around this specific direction, forming multiple other ion transport channels.

[0087] In some embodiments, the transition metal nanoparticles include at least one of iron nanoparticles, nickel nanoparticles, or cobalt nanoparticles. Further, the average particle size of the transition metal nanoparticles is 5 nm to 20 nm. As an example, the average particle size of the transition metal nanoparticles can be 5 nm, 10 nm, 15 nm, 20 nm, or a range consisting of any two of the above values.

[0088] In some embodiments, the method of "applying transition metal nanoparticles to the surface of boron nitride nanosheets" may include chemical plating, physical vapor deposition, or spin coating. Exemplarily, transition metal nanoparticles are dispersed in an organic solvent to obtain a spin coating solution, which is then uniformly coated onto the surface of boron nitride nanosheets by spin coating. After removing the organic solvent, the transition metal nanoparticles adhere to the surface of the boron nitride nanosheets.

[0089] The organic solvent can be ethanol or dimethylformamide (DMF), etc. The organic solvent can be removed by natural air drying or vacuum drying, etc.

[0090] In some embodiments, the heating temperature is 1000°C to 1500°C, and the heating rate is 5°C / min to 10°C / min. For example, the heating temperature is 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, or any combination of two of the above values; the heating rate is 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any combination of two of the above values.

[0091] By controlling the heating rate, the reaction can be made more uniform, which is conducive to the formation of a stable metal / boron nitride interface, thereby achieving more precise directional etching.

[0092] In some embodiments, the reducing gas includes hydrogen or ammonia, and the flow rate of the reducing gas is 50 ml / min to 100 ml / min, for example, 50 ml / min, 60 ml / min, 80 ml / min, 100 ml / min or any combination of two of the above values.

[0093] In some embodiments, the reaction time is 30 min to 120 min. For example, 30 min, 60 min, 90 min, 120 min, etc.

[0094] In some embodiments, after the ion transport channel etching is completed, excess transition metal nanoparticles can be removed by cleaning with a suitable solvent, such as ethanol or deionized water.

[0095] Understandably, in some embodiments, the transition metal nanoparticles may not be completely removed, and the magnetic properties of the residual transition metal nanoparticles may be beneficial to the orientation and arrangement of boron nitride nanosheets in a subsequent magnetic field.

[0096] In some embodiments, the average depth of the ion transport channel is 0.05 nm to 5 nm, and the average width is 0.05 nm to 30 nm. As an example, the average depth of the ion transport channel on the surface of the boron nitride nanosheet is 0.05 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or any combination of two of the above values; the average width is 0.05 nm, 0.1 nm, 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, or any combination of two of the above values.

[0097] In some embodiments, "fibrillable binder" refers to a binder that can undergo fibrillation under specific conditions (e.g., under high shear force) during the dry electrode fabrication process to form fibrous filaments. This type of binder forms a network structure by overlapping and entangled fibrous filaments to encapsulate positive electrode active materials and conductive agents, thereby bonding these components together to form an electrode film with certain strength and performance. In some embodiments, the fibrous adhesive is selected from at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polyacrylonitrile (PAN), preferably polytetrafluoroethylene (PTFE).

[0098] In some embodiments, the mixed powder also includes a conductive agent.

[0099] Furthermore, the conductive agents used in the embodiments of this application include zero-dimensional conductive agents (such as conductive carbon black), one-dimensional conductive agents (such as carbon nanotubes and carbon nanofibers), or two-dimensional conductive agents (such as graphene). Preferably, the conductive agents used in the embodiments of this application include one-dimensional conductive agents. One-dimensional conductive agents with a certain linear length are beneficial for further bonding with ion-conducting materials to construct a continuous ion and electron transport network.

[0100] In some embodiments, the conductive agents used in this application include magnetic conductive agents, such as magnetic carbon nanotubes or magnetic carbon nanofibers. These magnetic conductive agents can be purchased commercially or obtained through simple magnetic processing. Exemplarily, composite materials are formed by combining a one-dimensional conductive agent (e.g., carbon nanotubes) with magnetic materials (e.g., metal or metal oxide particles such as iron, cobalt, and nickel). For example, a composite of a one-dimensional conductive agent and a magnetic material, such as MnZnFe2O4, is prepared by sol-gel method, co-precipitation method, etc., so that the one-dimensional conductive agent and the magnetic material are uniformly mixed at the microscale, thereby acquiring magnetism. In some embodiments, the method for preparing the mixed powder includes: (1) A first powder is obtained by mixing a binder and an ion conductor material and applying a magnetic field to orient at least one ion transport channel of the ion conductor material along a predetermined direction. (2) The first powder, positive electrode active material and conductive agent are mixed and the binder is fiberized to form fiber filaments.

[0101] Furthermore, the method of mixing the binder and the ionic conductor material includes: continuously adding the ionic conductor material to the binder under stirring conditions. This continuous addition can be achieved by spray-drying followed by continuous spraying, or by spraying dry powder mixed with an airflow.

[0102] Furthermore, the methods for mixing the binder and the ionic conductor material include mixing under low-speed, constant-temperature conditions, such as a rotational speed of 5 m / s to 15 m / s and a temperature of 5°C to 25°C.

[0103] Understandably, the magnetic field can be applied as a continuous magnetic field, without specifying a predetermined direction, as long as the ion transport channels are aligned in the same direction. In this case, the ion conductor material can be uniformly embedded in the binder during the alignment process, and the viscosity of the binder is fixed to a certain extent.

[0104] In some embodiments, the fiberization step includes: (1) Under low temperature conditions, the first powder, the positive electrode active material and the conductive agent are mixed at a low speed to obtain the second powder; (2) While mixing the second powder at low speed, heat it up to pre-fiberize it and keep it warm for a period of time; (3) The second powder is mixed at high speed to complete the fiberization.

[0105] In some embodiments, the temperature under low-temperature conditions is 0°C to 15°C; the rotation speed of low-speed mixing is 5 m / s to 15 m / s; and the mixing time is 10 min to 60 min. Low-speed mixing under low-temperature conditions can prevent the binder from prematurely fiberizing, thereby affecting the mixing uniformity.

[0106] As an example, the temperature for low-temperature conditions is 0°C, 2°C, 5°C, 10°C, 15°C, or any combination of two of the above values; the rotational speed for low-speed mixing is 5 m / s, 6 m / s, 8 m / s, 10 m / s, 12 m / s, 15 m / s, or any combination of two of the above values; and the mixing time is 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, or any combination of two of the above values.

[0107] In some embodiments, the pre-fiberizing temperature is 60°C to 100°C, and the holding time is 15 min to 60 min. As an example, the pre-fiberizing temperature is 60°C, 80°C, 90°C, 100°C, or any combination of two of the above values; the holding time after reaching the temperature is 15 min, 20 min, 30 min, 50 min, 60 min, or any combination of two of the above values.

[0108] By gradually increasing the temperature under low-temperature and low-speed mixing conditions, the adhesive can maintain uniform contact with other components while gradually melting, thereby achieving full fiberization and uniform mixing.

[0109] In some embodiments, the high-speed mixing equipment is a high-speed mixer, and the mixing linear speed is 30m / s to 60m / s, for example, 30m / s, 40m / s, 50m / s, 60m / s or any two of the above values; the mixing time is 10min to 60min, for example, 10min, 20min, 30min, 50min, 60min or any two of the above values.

[0110] Furthermore, the blade edge of the high-speed mixer can be designed as an arc or elliptical structure, which can effectively solve the problem of the positive electrode active material being broken by the blade, thereby improving the problems of reduced specific capacity and cycle performance of dry electrode sheets.

[0111] In some embodiments, the equipment used for high-speed mixing is a supersonic airflow pulverizer, where the supersonic airflow is greater than 100 m / s, such as 100 m / s, 200 m / s, 300 m / s, etc.

[0112] By further high-temperature and high-speed mixing, the second powder is crushed and fiberized, so that the binder is fully fiberized to form a three-dimensional fiber structure, and ion conductor materials, positive electrode active materials and conductive agents can be uniformly embedded in the binder fiber structure.

[0113] In some embodiments, the average diameter of the fiber filaments of the fiberized adhesive is 10 nm to 100 nm, the average length is 1 μm to 100 μm, and the average aspect ratio is 10 to 10000. As an example, the average diameter of the fiber filaments of the fiberized adhesive is 10 nm, 20 nm, 30 nm, 50 nm, 100 nm, or any combination of two of the above values; the average length is 1 μm, 10 μm, 20 μm, 50 μm, 60 μm, 70 μm, 100 μm, or any combination of two of the above values; and the average aspect ratio is 10, 100, 500, 1000, 10000, or any combination of two of the above values.

[0114] In this embodiment of the application, the diameter and length of the fiber filaments are statistically analyzed by scanning electron microscopy (SEM) on the mixed powder sample and combined with image analysis software. The results are repeated 100 times to calculate the average diameter and average length. The average length-to-diameter ratio can then be obtained by dividing the average length by the average diameter.

[0115] S20: A magnetic field is applied to the mixed powder to orient it, and then it is hot-pressed to form a positive electrode film; wherein, under the action of the magnetic field, at least one ion transport channel of the ion conductor material is oriented and arranged along the thickness direction of the positive electrode film; the fiber filaments overlap each other to form a network structure during hot pressing. In some embodiments, step S20 includes: placing a hot-pressing mold in a magnetic field, adding the mixed powder into the hot-pressing mold, rotating the ion conductor material, and aligning at least one ion transport channel along the hot-pressing direction (i.e., the thickness direction of the positive electrode film). Subsequently, during the hot-pressing process, a continuous magnetic field is provided to assist the ion transport channels in maintaining their orientation, thereby forming the positive electrode film.

[0116] In some embodiments, the hot pressing method includes powder die casting. During the hot pressing process, the temperature is controlled at 80°C to 250°C, and the pressure is 1T to 50T. As an example, the hot pressing temperature is 80°C, 100°C, 150°C, 200°C, 220°C, 250°C, or any combination of two of the above values; the pressure is 1T, 5T, 10T, 20T, 50T, or any combination of two of the above values.

[0117] In this embodiment, powder die casting is used to prepare irregularly shaped batteries, such as L-shaped and T-shaped batteries, which can make full use of the spatial structure. It can solve the problems of insufficient fibrillation, different three-dimensional fibrillation and uneven mixing of various component materials in the prior art. The prepared positive electrode film has high strength, low internal resistance and good film-forming properties.

[0118] In some embodiments, the magnetic field strength of the applied magnetic field is 0.1T to 1T. As an example, the magnetic field strength of the applied magnetic field is 0.1T, 0.2T, 0.5T, 0.6T, 1T, or any range of two of the above values.

[0119] When the mixture also includes a one-dimensional conductive agent with magnetic properties (such as magnetic carbon nanotubes), after applying a magnetic field to the mixed powder for orientation, the length direction of the one-dimensional conductive agent is oriented and arranged in the thickness direction of the positive electrode film.

[0120] Specifically, "the length direction of the one-dimensional conductive agent is oriented along the thickness direction of the positive electrode film" means that the length direction of the one-dimensional conductive agent is all (or most of it) along the thickness direction of the positive electrode film, and the angle between the length direction of the one-dimensional conductive agent and the thickness direction of the positive electrode film is within 30°. Further, the length direction of the one-dimensional conductive agent is parallel to the thickness direction of the positive electrode film.

[0121] When the mixed powder also includes a magnetic one-dimensional conductive agent, under the combined action of high temperature, high pressure, and a magnetic field, the length direction of the magnetic conductive agent will align with the direction of the magnetic field, forming an ordered conductive network. Simultaneously, other materials will also be more uniformly distributed under the synergistic effect of hot pressing and the magnetic field, optimizing the microstructure of the positive electrode film. This continuous hot pressing-magnetic field synchronous directional molding technology facilitates continuous production of positive electrode films, significantly improving production efficiency and ensuring consistent product quality. By constructing an ordered conductive network and ion transport network, the rate charge-discharge performance and cycle stability of the battery under high load can be enhanced, meeting the dual requirements of product performance and production efficiency for engineering mass production.

[0122] In some embodiments, the thickness of the positive electrode film is 70 μm to 1000 μm, such as 70 μm, 100 μm, 150 μm, 200 μm, 500 μm, 800 μm, 100 μm or any two of the above values.

[0123] S30: Combine the positive electrode film and the positive electrode current collector to obtain the positive electrode sheet.

[0124] In some embodiments, the composite process can be as follows: the positive current collector and the positive electrode membrane are rolled together to obtain the positive electrode membrane.

[0125] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil or carbon-coated aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0126] In some embodiments, the compaction density of the positive electrode sheet can be 2.8 g / cm³. 3 ~4.2g / cm 3 For example, 2.8g / cm 3 3g / cm 3 3.2g / cm 3 3.5g / cm 3 4.2g / cm 3 Or a range consisting of any two of the above values.

[0127] In addition, this application also provides a secondary battery, including the above-mentioned positive electrode, negative electrode and separator disposed between the positive electrode and negative electrode.

[0128] Understandably, this application does not limit the type of secondary battery, which may include lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, etc. Similarly, this application does not specifically limit the selection and type of the negative electrode sheet and separator.

[0129] Example To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0130] In the embodiments and comparative examples of this application, the ion conductor material used is boron nitride nanosheets with ion transport channels, and the preparation method includes the following steps: (1) Disperse iron nanoparticles (average particle size of about 10 nm) in dimethylformamide (DMF) to obtain a coating solution. Place boron nitride nanosheets on a spin coater and coat the coating solution evenly on the surface of the boron nitride nanosheets.

[0131] (2) Boron nitride nanosheets coated with iron nanoparticles were placed in a reaction chamber equipped with a gas flow control device. Hydrogen gas (purity 99.9%) was introduced into the reaction chamber at a flow rate of 80 mL / min to remove air from the reaction chamber and create a reducing atmosphere. The reaction chamber was heated to 1000°C in a high-temperature furnace at a heating rate of 8°C / min, and the direction of the gas flow was controlled. The temperature was then maintained for 60 min to allow the iron nanoparticles and boron nitride nanosheets to undergo a catalytic reaction under high temperature and hydrogen gas. Multiple ion transport channels were etched in the planar direction of the boron nitride nanosheets, with at least one ion transport channel extending along the length of the boron nitride nanosheets.

[0132] (3) After the reaction is complete, stop heating and allow the reaction chamber to cool naturally to room temperature in a hydrogen atmosphere. Use ethanol to clean the surface of the boron nitride nanosheets to remove excess iron nanoparticles, and let them air dry to obtain boron nitride nanosheets with ion transport channels (hereinafter referred to as MBN).

[0133] Example 1 This embodiment provides a positive electrode sheet, the raw materials of which include lithium cobalt oxide (LiCoO2), conductive carbon black (SP), conductive carbon nanotubes (CNTs), ion conductor material (boron nitride nanosheets, hereinafter referred to as MBN, with a mass ratio of 3:1 between boron nitride nanosheets with an average sheet diameter of 30nm and an ionic conductivity of 0.158S / cm and boron nitride nanosheets with an average sheet diameter of 4μm and an ionic conductivity of 0.158S / cm), and binder polytetrafluoroethylene (PTFE), with a mass ratio of 95:1:1:1:2. The preparation method includes the following steps: (1) Add the fiberizable binder polytetrafluoroethylene (PTFE) and ion conductor material (MBN) to a high-speed mixer, stir at a linear speed of 10 m / s for 60 min at 10 °C, and apply a continuous magnetic field (magnetic field strength of 1 T) for orientation. After the powder is mixed evenly, the first powder is obtained.

[0134] (2) Beforehand, reduce the temperature of the mixing tank of the high-speed mixer (with elliptical blades) to 5°C, add lithium cobalt oxide (LiCoO2), conductive carbon black (SP) and conductive carbon nanotubes (CNTs) into the high-speed mixer, and stir at a low linear speed of 10 m / s for 15 min to form the second powder.

[0135] (3) Continue stirring at a low linear speed of 10 m / s and heat the mixing tank to 60°C. After reaching the temperature, continue stirring at a low linear speed of 10 m / s for 20 min to allow the binder to achieve a crystal transformation (i.e., pre-fiberization).

[0136] (4) Then the pre-fiberized second powder is stirred at a high speed of 40 m / s to obtain a fluffy mixed powder. The average diameter of the obtained fiber filaments is 17 nm, the average length is 50 μm, and the average aspect ratio is about 3000.

[0137] (5) Add the mixed powder to the powder die casting machine and apply a continuous and stable magnetic field (magnetic field strength of 1T) to orient the MBN. Set the die casting cavity temperature to 200℃ and die cast under 10T pressure to obtain a positive electrode film with a thickness of 100μm.

[0138] (6) The positive electrode film is hot-pressed onto the carbon-coated aluminum foil using a hot rolling press to obtain the positive electrode sheet, wherein the compaction density of the positive electrode sheet is 4.2 g / cm³. 3 .

[0139] The morphology of the positive electrode sheet prepared in Example 1 was analyzed. Figure 4 This is a scanning electron microscope (SEM) image of the positive electrode sheet provided in Embodiment 1 of this application, from... Figure 4 As can be seen, boron nitride nanosheets (indicated by white arrows) and the positive electrode active material are uniformly dispersed in the network structure of the fibrous binder, and the planar direction of the boron nitride nanosheets is oriented along the thickness direction of the positive electrode film. Furthermore, some fibers are attached to the surface of the positive electrode active material, and boron nitride nanosheets are adhered to the fibers. Additionally, since the ion transport channels in the boron nitride nanosheets are nanoscale and cannot be clearly identified due to the orientation angle, ion transport channels oriented along the thickness direction of the positive electrode film can be partially identified from the white circle. Since only boron nitride nanosheets contain nitrogen in the raw material of the positive electrode in Example 1, the distribution of boron nitride nanosheets can be represented by the distribution of nitrogen in the positive electrode film. Figure 5 This is an EDS cross-sectional view of the nitrogen element in the positive electrode film provided in Embodiment 1 of this application. Figure 6 for Figure 5 A magnified view of a portion of the image. From Figure 5 and Figure 6 As can be seen, boron nitride nanosheets are uniformly distributed in the positive electrode film, and in any 2μm × 2μm region ( Figure 6 The boxes in the middle (red square) all contain boron nitride nanosheets.

[0140] Example 2 This embodiment provides a positive electrode sheet, the preparation method of which is roughly the same as that in Example 1, except that: The ion conductor material is boron nitride nanosheets with an average sheet diameter of 30 nm and an ionic conductivity of 0.158 S / cm.

[0141] Example 3 This embodiment provides a positive electrode sheet, the preparation method of which is roughly the same as that in Example 1, except that: The ion conductor material is boron nitride nanosheets with an average sheet diameter of 4 μm and an ionic conductivity of 0.158 S / cm.

[0142] Example 4 This embodiment provides a positive electrode sheet, the preparation method of which is roughly the same as that in Example 1, except that: The mass percentage of the ion conductor material was adjusted from 1 wt% to 5 wt%. The mass ratio of lithium cobalt oxide (LiCoO2), conductive carbon black (SP), conductive carbon nanotubes (CNTs), ion conductor material, and binder polytetrafluoroethylene (PTFE) was 91:1:1:1:2.

[0143] Example 5 This embodiment provides a positive electrode sheet, the preparation method of which is roughly the same as that in Example 1, except that: No magnetic field is applied during orientation in step (1).

[0144] Comparative Example 1 This comparative example provides a positive electrode sheet, the preparation method of which differs from that of Example 1 in that: In step (1), no ionic conductor material is added, and the mass ratio of lithium cobalt oxide (LiCoO2), conductive carbon black (SP), conductive carbon nanotubes (CNTs) and binder polytetrafluoroethylene (PTFE) is 95:1.5:1.5:2.

[0145] Comparative Example 2 This comparative example provides a positive electrode sheet, the preparation method of which differs from that of Example 1 in that: Replacing boron nitride nanosheets with ion transport channels with unmodified conventional boron nitride nanosheets (i.e., those without ion transport channels) resulted in an ionic conductivity of 6.47 × 10⁻⁶. -6 S / cm.

[0146] Comparative Example 3 This comparative example provides a positive electrode sheet, the preparation method of which differs from that of Example 1 in that: In both steps (1) and (5), a magnetic field is applied for orientation.

[0147] Performance testing and results analysis 1. Positive electrode sheet The positive electrode sheets prepared in the examples and comparative examples were subjected to performance tests. The specific test methods are as follows, and the test results are shown in Table 1.

[0148] (1) Resistivity: The resistivity was tested using an electrode resistance meter. In an environment with a room temperature of 25℃ and a dew point of -40℃ (used to indicate air humidity), the prepared positive electrode was placed on the resistance meter table to make its surface flat. The pressure gauge was adjusted to fix the test electrode and ensure that the probe and the electrode made good contact. The resistivity of the positive electrode was obtained in sequence.

[0149] (2) Ionic conductivity: Assemble the positive electrode into a single-layer symmetrical cell, add electrolyte and LiIn to each side, place it on an electrochemical workstation to test electrochemical impedance spectroscopy (EIS), set the frequency to 0.5Hz~200kHz, and the perturbation voltage to 10mV; calculate the ionic resistance Rion of the positive electrode through the intersection of the two straight lines of EIS, and the electrode ionic conductivity = d (electrode thickness) / (Rion * A (electrode area)).

[0150] (3) Peel strength: The peel strength tester was used. At a room temperature of 25°C and a dew point of -40°C, the current collector side of the prepared positive electrode sheet was attached to the working panel with test double-sided tape. The surface of the electrode film and the peel strength tester were connected with test tape. The peel speed was set to 60 mm / min and the peel angle was 180°. The peel strength of the positive electrode sheet was tested and recorded in sequence.

[0151] 2. Secondary batteries The prepared positive electrode, lithium metal negative electrode, separator, and electrolyte were assembled to form a coin cell. The cells were charged and discharged at 1C and 3C rates at 25°C, respectively. The discharge specific capacity was recorded sequentially, and the first-efficiency at 1C rate was calculated.

[0152] Table 1 Performance test results of positive electrode and battery

[0153] As can be seen from Table 1, compared with Comparative Examples 1 to 3, the positive electrode sheets prepared in Examples 1 to 5 of this application have higher ionic conductivity, higher peel strength and lower resistivity, and the corresponding batteries prepared have higher discharge specific capacity at both 1C and 3C rates. Figure 7 The first charge-discharge curves of the batteries in Examples 1-5 and Comparative Examples 1-3 at a 1C rate are shown in Table 1 and... Figure 7 It can be seen that the batteries prepared according to Examples 1 to 5 of this application also have high initial efficiency.

[0154] A comparison of Examples 1-3 shows that mixing large-diameter and small-diameter boron nitride nanosheets can effectively improve the ion transport performance of the electrode and reduce its resistivity, thereby enhancing the battery's specific capacity, rate charge / discharge performance, and initial efficiency. A comparison of Examples 1 and 4 shows that by further controlling the amount of ion conductor material added, its distribution within the positive electrode film becomes more uniform, and the interfacial reaction between the active material and the electrolyte is avoided, thus further improving battery performance. A comparison of Examples 1 and 5 shows that by performing a magnetic field orientation during the mixing of the binder and ion conductor material, the ion conductor material is embedded in the binder, resulting in a more uniform distribution and the formation of stable and oriented ion transport channels. This helps to further improve the ion transport performance of the electrode and significantly reduce its resistivity, thereby further enhancing battery performance.

[0155] Comparing Example 1 with Comparative Examples 1 to 3, it can be seen that Comparative Example 1 does not add ion conductor materials, Comparative Example 2 adds ion conductor materials without ion transport channels, and Comparative Example 3 does not orient the ion conductor materials, resulting in a significant reduction in the performance of both the electrode and the battery.

[0156] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A positive electrode plate, characterized in that, The device includes a positive current collector and a positive electrode membrane attached to at least one side surface of the positive current collector. The positive electrode membrane includes a network structure formed by filaments of a fibrous binder, a positive active material and an ion conductor material dispersed in the network structure, and the ion conductor material having at least one ion transport channel and the ion transport channel being oriented along the thickness direction of the positive electrode membrane. The ionic conductivity of the ionic conductor material is not less than 0.02 S / cm; the thickness of the positive electrode film ranges from 30 μm to 2000 μm.

2. The positive electrode sheet according to claim 1, characterized in that, The ion conductor material includes at least one first ion transport channel and a plurality of second ion transport channels. The first ion transport channels are oriented along the thickness direction of the positive electrode film, and the second ion transport channels are connected to the first ion transport channels.

3. The positive electrode sheet according to claim 1, characterized in that, Multiple ion conductor materials are sequentially overlapped along the thickness direction of the positive electrode film, and the ion transport channels of the multiple ion conductor materials are sequentially connected.

4. The positive electrode sheet according to claim 1, characterized in that, At least a portion of the fibers are adhered to the surface of the positive electrode active material, and the ion conductor material is attached to the fibers.

5. The positive electrode sheet according to claim 1, characterized in that, Any 2μm × 2μm region in the longitudinal section of the positive electrode membrane contains the ion conductor material.

6. The positive electrode sheet according to claim 1, characterized in that, The ion conductor material includes at least one of boron nitride nanosheets, graphene, oxide solid electrolyte, sulfide solid electrolyte, or nanowires.

7. The positive electrode sheet according to claim 1, characterized in that, The ionic conductor material includes boron nitride nanosheets.

8. The positive electrode sheet according to claim 7, characterized in that, The average diameter of the boron nitride nanosheets is 1 nm to 10 μm.

9. The positive electrode sheet according to claim 1, characterized in that, Based on the total mass of the positive electrode membrane, the mass percentage of the ion conductor material is 0.2wt% to 10wt%.

10. The positive electrode sheet according to claim 1, characterized in that, The fiber filaments of the fiberized adhesive have an average diameter of 10 nm to 100 nm, an average length of 1 μm to 100 μm, and an average aspect ratio of 10 to 10000.

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that, The positive electrode film also includes a conductive agent; the conductive agent accounts for 0.2wt% to 5wt% of the total mass of the positive electrode film.

12. A method for preparing a positive electrode sheet as described in any one of claims 1 to 11, characterized in that, Includes the following steps: A fiberizable binder, the positive electrode active material, and the ion conductor material are mixed, and the binder is fiberized to form filaments to obtain a mixed powder. A magnetic field is applied to the mixed powder to orient it, followed by hot pressing to form a positive electrode film; wherein, under the action of the magnetic field, at least one ion transport channel of the ion conductor material is oriented and arranged along the thickness direction of the positive electrode film; the fibers overlap each other to form a network structure during hot pressing. The positive electrode film and the positive electrode current collector are combined to obtain a positive electrode sheet.

13. The preparation method according to claim 12, characterized in that, The ion conductor material includes boron nitride nanosheets, and at least one of the ion transport channels extends along the planar direction of the boron nitride nanosheets. The method of applying a magnetic field to the mixed powder for orientation includes: applying a magnetic field to the mixed powder such that the planar direction of the boron nitride nanosheets is oriented and arranged in the thickness direction of the positive electrode film.

14. The preparation method according to claim 12, characterized in that, The method for preparing the mixed powder includes: The binder and the ion conductor material are mixed, and a magnetic field is applied to cause at least one of the ion transport channels of the ion conductor material to be oriented in a predetermined direction to obtain a first powder. The first powder, the positive electrode active material, and the conductive agent are mixed, and the binder is fiberized to form the fiber filaments; Optionally, the method of mixing the binder and the ionic conductor material includes: continuously adding the ionic conductor material to the binder under stirring conditions.

15. The preparation method according to claim 14, characterized in that, The fiberization step includes: Under low-temperature conditions, the first powder, the positive electrode active material, and the conductive agent are mixed at a low speed to obtain the second powder; The second powder is heated while being mixed at a low speed to pre-fiberize it, and then kept at that temperature for a period of time. The second powder is mixed at high speed to complete the fiberization.

16. A secondary battery, characterized in that, Including the positive electrode sheet as described in any one of claims 1 to 11.

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