Battery cell and preparation method therefor, solid-state battery and electric device

Abstract

The present application relates to the technical field of batteries, and provides a battery cell and a preparation method therefor, a solid-state battery and an electric device. The battery cell of the present application comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer attached to the surface of the positive electrode current collector; the positive electrode film layer comprises a positive electrode active material, a sulfide solid-state electrolyte and cellulose; at least part of the sulfide solid-state electrolyte is distributed along the extension direction of the cellulose; and at least part of the cellulose is in contact with part of the surface of the positive electrode active material. The cellulose and the sulfide solid-state electrolyte form linear long-range ion transport, which is beneficial for improving an ion transport effect, thereby improving the first-cycle specific discharge capacity and the initial Coulombic efficiency of the solid-state battery. Furthermore, the contact area between the sulfide solid-state electrolyte and the positive electrode active material and the confinement ability of the sulfide solid-state electrolyte for the positive electrode active material can also be increased, thereby improving the cycle performance of the solid-state battery, and further improving the first-cycle specific discharge capacity and the initial Coulombic efficiency of the solid-state battery.

Description

Battery cells and their preparation methods, solid-state batteries and electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese patent application CN202510305140.8, filed on March 14, 2025, entitled “Battery cell and preparation method thereof, solid-state battery and power device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and more specifically, to a battery cell and its preparation method, a solid-state battery, and an electrical device. Background Technology

[0004] Solid-state batteries typically consist of a positive electrode, a negative electrode, and a solid electrolyte membrane disposed between the positive and negative electrodes. To optimize ion conduction, a small amount of solid electrolyte is usually added to the positive electrode. Sulfide solid electrolytes are considered the most ideal solid electrolyte materials for solid-state batteries due to their high ionic conductivity and excellent mechanical ductility.

[0005] Sulfide solid electrolytes are micro- or nano-sized spherical or sheet-like particles that achieve ion transport between the positive electrode and the positive electrode active material through solid-solid contact. However, the ion transport performance of sulfide solid electrolytes in existing solid-state batteries is poor, resulting in the need to improve the first-cycle discharge specific capacity and first-cycle coulombic efficiency (hereinafter referred to as first efficiency) of solid-state batteries. Summary of the Invention

[0006] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell and its preparation method, a solid-state battery and an electrical device, which aims to improve the ion transport effect of the positive electrode, thereby improving the first-cycle discharge specific capacity and first-cycle efficiency of the battery.

[0007] The first aspect of this application provides a battery cell, the battery cell including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer attached to the surface of the positive current collector, the positive electrode film layer including a positive electrode active material, a sulfide solid electrolyte and cellulose; at least a portion of the sulfide solid electrolyte is distributed along the extension direction of the cellulose, and at least a portion of the cellulose is in contact with a portion of the surface of the positive electrode active material.

[0008] In the above technical solution, by introducing sulfide solid electrolyte and cellulose into the positive electrode film layer, and with at least a portion of the sulfide solid electrolyte distributed along the extension direction of the cellulose, the gap between the sulfide solid electrolyte particles is reduced, forming linear long-range ion transport, which is beneficial to improving the ion transport effect, thereby increasing the first-cycle discharge specific capacity and first-cycle efficiency of the solid-state battery. Furthermore, the sulfide solid electrolyte extends and distributes on the surface of the cellulose, and the cellulose easily distributes around the positive electrode active material, with at least a portion of the cellulose in contact with a portion of the positive electrode active material surface. This also increases the contact area between the sulfide solid electrolyte and the positive electrode active material particles, as well as the binding ability of the sulfide solid electrolyte on the positive electrode active particles, alleviating the volume change of the positive electrode active material during cycling, thereby improving the cycle performance of the solid-state battery and further increasing the first-cycle discharge specific capacity and first-cycle efficiency.

[0009] In some embodiments, the sulfide solid electrolyte, comprising ≥30% of the total content, is distributed along the extension direction of the cellulose. In the positive electrode film, a higher proportion of the sulfide solid electrolyte arranged along the cellulose extension direction is beneficial for improving ion transport, thereby increasing the first-cycle discharge specific capacity and first-cycle efficiency of the solid-state battery. Furthermore, it can further increase the contact area between the sulfide solid electrolyte and the positive electrode active material particles, as well as the binding ability of the sulfide solid electrolyte to the positive electrode active particles, thus improving the cycle performance of the solid-state battery.

[0010] In some embodiments, the cellulose includes sulfonated modified cellulose. Sulfonated modified cellulose has sulfonic acid groups (-SO3H), which, after ionization in the dispersion, readily bind to metal cations (such as lithium ions) in the sulfide solid electrolyte. The interaction between the sulfonic acid groups and the metal cations is strong and the binding is tight, which is beneficial for inducing the orderly arrangement of the sulfide solid electrolyte on the cellulose surface during the drying process, so as to achieve the orderly distribution of the sulfide solid electrolyte along the extension direction of the cellulose.

[0011] In some embodiments, the cellulose includes at least one of sulfonated modified ethyl cellulose, sulfonated modified methyl cellulose, or sulfonated modified cyanocellulose. All of the above celluloses contain sulfonic acid groups (-SO3H), which can tightly bind to metal cations (such as lithium ions) in the sulfide solid electrolyte, thereby effectively achieving an orderly distribution of the sulfide solid electrolyte along the extension direction of the cellulose.

[0012] In some embodiments, the weight-average molecular weight of cellulose is 50,000 to 2.5 million. Controlling the weight-average molecular weight of cellulose within a suitable range is beneficial for the uniform dispersion of cellulose itself and the sulfide solid electrolyte.

[0013] In some embodiments, the average length of cellulose is 0.2 mm to 20 mm, the average diameter is 5 μm to 20 μm, and the average aspect ratio of cellulose is 20 to 2000. By controlling the average length, average diameter, and average aspect ratio of cellulose within the above-mentioned suitable ranges, a greater number of sulfide solid electrolyte particles can be distributed on the surface of the cellulose, and the binding ability of the sulfide solid electrolyte to the positive electrode active material particles can be further increased, thereby further improving the cycle performance of the solid-state battery.

[0014] In some embodiments, the average particle size of the sulfide solid electrolyte is 0.5 μm to 5 μm. By controlling the average particle size of the sulfide solid electrolyte within a suitable range, it is beneficial to increase the contact with the positive electrode active material and to ensure uniform distribution on the cellulose surface, thus avoiding agglomeration.

[0015] In some embodiments, the mass percentage of cellulose is 0.1% to 2% based on the mass of the positive electrode film; further, the mass percentage of cellulose is 0.1% to 0.9% based on the mass of the positive electrode film. A suitable mass percentage of cellulose allows for the distribution of sulfide solid electrolyte on most of the cellulose surface, and also allows for the distribution of most of the sulfide solid electrolyte on the cellulose surface.

[0016] In some embodiments, the sulfide solid electrolyte accounts for 6% to 20% of the mass of the positive electrode film. Further, based on the mass of the positive electrode film, the sulfide solid electrolyte accounts for 6% to 15% of the mass. Maintaining a suitable mass percentage of the sulfide solid electrolyte within this range ensures a certain level of control over the amount of positive electrode active material and also improves ion transport performance.

[0017] In some embodiments, the mass ratio of cellulose to sulfide solid electrolyte is 1:(5~60). Further, the mass ratio of cellulose to sulfide solid electrolyte is 1:(15~60). By controlling the mass ratio of cellulose to sulfide solid electrolyte within a suitable range, more sulfide solid electrolyte can be distributed along the extension direction of cellulose, thereby further improving the ion transport effect.

[0018] The second aspect of this application provides a method for preparing a battery cell, comprising the following steps: dispersing and drying a mixture containing cellulose and sulfide solid electrolyte to obtain a mixture; wherein the cellulose carries a negative charge in the mixture; mixing the mixture with a positive electrode active material to form a positive electrode mixture; using the positive electrode mixture to form a positive electrode film layer on the surface of a positive electrode current collector to obtain a positive electrode sheet; assembling the positive electrode sheet, the negative electrode sheet, and the solid electrolyte film to obtain a battery cell.

[0019] In the above technical solution, cellulose and sulfide solid electrolyte are first dispersed separately, so that the cellulose carries a negative charge in the mixture. The negative charge in the cellulose can combine with the metal cations (such as lithium ions) in the sulfide solid electrolyte, inducing at least a portion of the sulfide solid electrolyte to distribute along the extension direction of the cellulose during the drying process. Then, the mixture is mixed with the positive electrode active material, which can form linear long-range ion transport in the positive electrode film layer, which is beneficial to improving the ion transport effect, thereby improving the first-cycle discharge specific capacity and first-cycle efficiency of the solid-state battery. In addition, the sulfide solid electrolyte extends and distributes on the surface of cellulose, and cellulose is easily distributed around the positive electrode active material. At least a portion of the cellulose is in contact with part of the surface of the positive electrode active material, which can also increase the contact area between the sulfide solid electrolyte and the positive electrode active material particles and the binding ability of the sulfide solid electrolyte on the positive electrode active particles, alleviate the volume change of the positive electrode active material during cycling, thereby improving the cycle performance of the solid-state battery and further improving the first-cycle discharge specific capacity and first-cycle efficiency of the solid-state battery.

[0020] In some embodiments, the solid content of the mixture is 50% to 80%. By controlling the solid content of the mixture, the cellulose and sulfide solid electrolytes can be dispersed more evenly.

[0021] In some embodiments, the zeta potential of the mixture is -30mV to -80mV. By controlling the zeta potential of the mixture within a suitable range, a sufficient number of negative charges can be controlled on the cellulose surface, thereby enabling the effective binding of a sufficient number of sulfide solid electrolytes on its surface. This induces a sufficient number of sulfide solid electrolytes to arrange themselves in an orderly manner on the cellulose surface, achieving an orderly distribution of more sulfide solid electrolytes along the extension direction of the cellulose.

[0022] In some embodiments, the cellulose includes sulfonated modified cellulose. Sulfonated modified cellulose has sulfonic acid groups (-SO3H), which readily bind to metal cations (such as lithium ions) in the sulfide solid electrolyte, and the interaction between the sulfonic acid groups and the metal cations is strong and the binding is tight, which is beneficial for inducing the orderly arrangement of the sulfide solid electrolyte on the cellulose surface, so as to achieve the orderly distribution of the sulfide solid electrolyte along the extension direction of cellulose.

[0023] In some embodiments, the cellulose includes at least one of sulfonated modified ethyl cellulose, sulfonated modified methyl cellulose, or sulfonated modified cyanocellulose. All of these celluloses contain sulfonic acid groups, which readily bind to metal cations on the surface of the sulfide solid electrolyte in the mixture, thereby achieving an orderly distribution of the sulfide solid electrolyte along the extension direction of the cellulose.

[0024] In some embodiments, the weight-average molecular weight of cellulose is 50,000 to 2.5 million. By controlling the weight-average molecular weight of cellulose within a suitable range, it is beneficial for cellulose itself and the sulfide solid electrolyte to be uniformly dispersed in the mixture.

[0025] In some embodiments, the average length of cellulose is 0.2 mm to 20 mm, and the average diameter is 5 μm to 20 μm; the average aspect ratio of cellulose is 20 to 2000. By controlling the average length, average diameter, and average aspect ratio of cellulose within the above-mentioned suitable ranges, a greater number of sulfide solid electrolyte particles can be distributed on the surface of the cellulose during the dispersion of the mixture; and during the mixing process with the positive electrode active material, the binding ability of the sulfide solid electrolyte to the positive electrode active material particles is increased, thereby further improving the cycle performance of the solid-state battery.

[0026] In some embodiments, the average particle size of the sulfide solid electrolyte is 0.5 μm to 5 μm. By controlling the average particle size of the sulfide solid electrolyte within a suitable range, it is beneficial to distribute it more evenly on the cellulose surface during the dispersion of the mixture, and to increase the contact between the electrolyte and the positive electrode active material during mixing.

[0027] In some embodiments, the mass ratio of cellulose to sulfide solid electrolyte in the mixture is 1:(5~60). By controlling the appropriate ratio of cellulose to sulfide solid electrolyte in the mixture, more sulfide solid electrolyte can be distributed along the extension direction of cellulose during the mixing and dispersion process, thereby further improving the ion transport effect.

[0028] In some embodiments, the cellulose content is 0.1% to 2% by mass, based on the mass of the cathode mixture. A suitable cellulose content allows for the distribution of sulfide solid electrolytes on most of the cellulose surface, or for most of the sulfide solid electrolytes to be distributed on the cellulose surface.

[0029] In some embodiments, the mass percentage of the sulfide solid electrolyte is 6% to 20% based on the mass of the cathode mixture. By controlling the mass percentage of the sulfide solid electrolyte within a suitable range, most of the sulfide solid electrolyte can be distributed on the surface of the cellulose during the dispersion of the mixture, and the proportion of the cathode active material can be maintained during the mixing process with the cathode active material.

[0030] The third aspect of this application provides a solid-state battery, including the battery cell of the first aspect of this application, or the battery cell prepared by the preparation method of the second aspect of this application.

[0031] A fourth aspect of this application provides an electrical device including a solid-state battery as described in the third aspect of this application. Attached Figure Description

[0032] 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.

[0033] Figure 1 is a schematic diagram of the distribution of sulfide solid electrolyte and cellulose in the positive electrode sheet of an embodiment of this application.

[0034] Figure 2 is a schematic diagram of a battery cell according to one embodiment of this application.

[0035] Figure 3 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 2.

[0036] Figure 4 is a schematic diagram of a battery module according to one embodiment of this application.

[0037] Figure 5 is a schematic diagram of a solid-state battery according to an embodiment of this application.

[0038] Figure 6 is an exploded view of a solid-state battery according to an embodiment of this application, as shown in Figure 5.

[0039] Figure 7 is a schematic diagram of an electrical device using a solid-state battery as a power source according to an embodiment of this application.

[0040] Figure 8 is a cross-sectional view of the positive electrode sheet in Embodiment 1 of this application obtained by transmission electron microscopy (TEM).

[0041] Explanation of reference numerals in the attached diagram: 1-Solid-state battery; 2-Upper casing; 3-Lower casing; 4-Battery module; 5-Battery cell; 51-Casing; 52-Electrode assembly; 53-Cover plate; A-Sulfide solid electrolyte; B-Cellulose; C-Positive electrode active material. Embodiments of the present invention

[0042] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, the method for preparing the battery cell, the solid-state battery, and the power application device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0043] 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.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0045] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0046] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0047] Solid-state batteries typically consist of a positive electrode, a negative electrode, and a solid electrolyte membrane disposed between the positive and negative electrodes. To optimize ion conduction and improve solid-solid interface contact, a small amount of solid electrolyte is usually added to the positive electrode. Currently, sulfide solid electrolytes have become a relatively ideal solid electrolyte material for solid-state batteries due to their high ionic conductivity and excellent mechanical ductility. However, their air stability is poor, easily reacting with water in the air to generate toxic H2S gas, reducing the ionic conductivity of the material and thus affecting the long-term cycle stability of the solid-state battery. To improve the air stability of sulfide solid electrolytes, a common approach in existing technologies is to dope them with elements such as O and Br, thereby stabilizing the crystal structure of the material and improving air stability. However, these methods cannot effectively isolate the sulfide solid electrolyte from air in the long term, and therefore do not effectively improve the long-term cycle stability of the solid-state battery.

[0048] Existing research has disclosed methods to reduce the amount of sulfide solid electrolyte used by selecting small-particle sulfide solid electrolytes, such as those with a particle size D50 < 500 nm, thereby improving the contact ability between the sulfide solid electrolyte and the active material particles. However, the preparation process of small-particle sulfide solid electrolytes is cumbersome and costly, and they are difficult to disperse during preparation, easily agglomerating, which is detrimental to ion transport. Furthermore, some studies have used external pressure to ensure contact between the sulfide solid electrolyte particles and the positive electrode active material particles, which is clearly not conducive to large-scale practical application.

[0049] Based on this, this application proposes a battery cell that introduces a sulfide solid electrolyte and cellulose into the positive electrode film layer. The sulfide solid electrolyte is distributed along the extension direction of the cellulose, reducing the gaps between sulfide solid electrolyte particles and forming linear long-range ion transport, which improves ion transport efficiency and thus increases the first-cycle discharge specific capacity and first-cycle efficiency of the solid-state battery. Furthermore, the sulfide solid electrolyte extends and distributes on the cellulose surface, allowing at least a portion of the cellulose to contact a portion of the positive electrode active material surface. The cellulose easily distributes around the positive electrode active material, increasing the contact area between the sulfide solid electrolyte and the positive electrode active material particles, as well as the binding ability of the sulfide solid electrolyte to the positive electrode active particles. This alleviates the volume change of the positive electrode active material during cycling, thereby improving the cycle performance of the solid-state battery and further enhancing its first-cycle discharge specific capacity and first-cycle efficiency.

[0050] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0051] [Battery cell]

[0052] This application provides a battery cell, which includes a positive electrode sheet, a positive current collector, and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, a sulfide solid electrolyte, and cellulose. At least a portion of the sulfide solid electrolyte is distributed along the extension direction of the cellulose, and at least a portion of the cellulose is in contact with a portion of the surface of the positive electrode active material.

[0053] In this application, the battery cell is a solid-state battery cell, and may further include a negative electrode and a solid electrolyte membrane disposed between the positive and negative electrode. The preparation method of the battery cell may include: sequentially stacking the positive electrode, the solid electrolyte membrane, and the negative electrode, and then bonding them together under pressure at a certain temperature to obtain the battery cell.

[0054] In this application, "at least a portion of the sulfide solid electrolyte is distributed in the direction of cellulose extension" means that a portion of the sulfide solid electrolyte may be distributed in the positive electrode film layer, and this portion of the sulfide solid electrolyte may not be distributed in the direction of cellulose extension.

[0055] "Distributed according to the extension direction of cellulose" means that: cellulose can extend in a straight direction, with some sulfide electrolytes accumulating around the cellulose in a circumferential direction, directly or indirectly contacting the cellulose. Along the extension direction of the cellulose, the sulfide electrolytes are arranged with almost small spacing (nanometer distance) or / and in contact with each other around the cellulose. Alternatively, cellulose can extend in a curved direction. This curved cellulose can be placed around the positive electrode active material or not. For cellulose placed around the positive electrode active material, after the sulfide solid electrolyte accumulates around it, more of the sulfide solid electrolyte is distributed around the positive electrode active material, thus having a binding effect on the positive electrode active material. Of course, the same cellulose can be partially distributed curvedly around the active material and partially directly distributed in the positive electrode film layer. Other areas; cellulose can also be wound and extended. The cellulose extending in this winding direction can be placed around the positive electrode active material or not placed around the positive electrode active material. For cellulose placed around the positive electrode active material, after the sulfide solid electrolyte accumulates around it, the sulfide solid electrolyte is more distributed around the positive electrode active material so as to have a binding effect on the positive electrode active material. Of course, the same cellulose can be partly wound and distributed around the positive electrode active material, and partly directly distributed in other areas of the positive electrode film layer. For cellulose extending in the winding direction, after the sulfide solid electrolyte is distributed, it may look similar to the aggregation of sulfide solid electrolyte. However, in fact, due to the inductive effect of cellulose, the sulfide solid electrolyte is more concentrated around the cellulose, and it can still play a good ion transport role.

[0056] In this application, "at least some of the cellulose is in contact with a portion of the surface of the positive electrode active material" means that at least some of the linear cellulose is distributed around the positive electrode active material, and the middle surface or end that is not covered by the sulfide solid electrolyte is in contact with a portion of the surface of the positive electrode active material. In this case, the sulfide solid electrolyte on the surface of the cellulose can be more distributed around the positive electrode active material, or even in contact with the rest of the surface of the positive electrode active material, thereby binding the positive electrode active material together with the cellulose.

[0057] Figure 1 is a schematic diagram showing the distribution of sulfide solid electrolyte and cellulose in the positive electrode sheet according to an embodiment of this application. As can be seen from Figure 1, the sulfide solid electrolyte A is uniformly and orderly distributed on the surface of cellulose B. The sulfide solid electrolyte A and cellulose B form a "beaded" structure with close contact between them. Furthermore, cellulose B can be disposed around the positive electrode active material C, allowing some cellulose B to contact a portion of the surface of the positive electrode active material C. The sulfide solid electrolyte A distributed on the surface of cellulose B also contacts a portion of the surface of the positive electrode active material C, thereby achieving a certain binding effect on the positive electrode active material C.

[0058] In some embodiments, ≥30% of the sulfide solid electrolyte is distributed along the extension direction of the cellulose. As an example, the percentage of sulfide solid electrolyte distributed along the extension direction of the cellulose can be 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc.

[0059] The proportion of sulfide solid electrolytes distributed along the cellulose extension direction can be determined using conventional methods or equipment in the art. As an example, a battery cell is disassembled, the positive electrode is taken, and it is cleaned by immersing it in dimethyl carbonate (DMC) solvent, then dried, and immersed in liquid nitrogen for 3 minutes. After removal, it is broken / cut with scissors to expose the cross-section, which is then attached to a sample stage for TEM testing to obtain a cross-sectional TEM image. The amount of sulfide solid electrolytes distributed along the cellulose extension direction and the amount of free and dispersed sulfide solid electrolytes are estimated in the TEM image, thereby calculating the proportion of sulfide solid electrolytes distributed along the cellulose extension direction.

[0060] In some embodiments, the cellulose comprises sulfonated modified cellulose. Further, the cellulose comprises at least one of sulfonated modified ethyl cellulose, sulfonated modified methyl cellulose, or sulfonated modified cyanocellulose.

[0061] "Sulfonated modified cellulose" refers to cellulose with sulfonic acid groups obtained by sulfonating cellulose. Sulfonated modified cellulose can be purchased directly from commercially available products or obtained through conventional sulfonation treatment of cellulose. As an example, a sulfonating agent (such as concentrated sulfuric acid, chlorosulfonic acid, etc.) can be slowly added dropwise to a cellulose solution at low temperatures (e.g., 0°C to 5°C) to carry out the sulfonation reaction. After the reaction is complete, neutralization is performed using a neutralizing agent (such as sodium hydroxide), followed by filtration and drying to obtain sulfonated modified cellulose.

[0062] In other embodiments, cellulose can be modified in other ways to induce the arrangement of sulfide electrolytes, such as carboxymethylation, carboxylation, and phosphate esterification.

[0063] In some embodiments, the weight-average molecular weight of cellulose is 50,000 to 2,500,000. As examples, the weight-average molecular weight of cellulose is 50,000, 100,000, 500,000, 1,000,000, 1,500,000, 2,000,000, 2,500,000, etc.

[0064] The term "weight-average molecular weight" refers to the sum of the products of the weight fraction of molecules with different molecular weights in a cellulose polymer and their corresponding molecular weights.

[0065] In some embodiments, the average length of the cellulose is 0.2 mm to 20 mm, and the average diameter is 5 μm to 20 μm. As an example, the average length of the cellulose is 0.2 mm, 0.5 mm, 1 mm, 5 mm, 10 mm, 15 mm, 20 mm, etc., and the average diameter is 5 μm, 10 μm, 15 μm, 20 μm, etc.

[0066] In some embodiments, the average aspect ratio of cellulose is 20 to 2000. As examples, the average aspect ratio of cellulose is 20, 50, 100, 200, 500, 1000, 1500, 2000, etc.

[0067] The average aspect ratio is the ratio of the average length to the average diameter. The average diameter and average length of the cellulose fibers can be tested using methods and equipment known in the art. As an example, the following steps can be taken: Take a positive electrode sheet, scrape off powder using a blade to obtain a sample of the positive electrode film layer, photograph the sample using a scanning electron microscope (e.g., ZEISS Sigma 300), and measure it according to the scale to determine the diameter and length of the cellulose fibers. Measure the diameter and length of 100 cellulose fibers, take the average value, and the ratio of the two is the average aspect ratio.

[0068] In some embodiments, the sulfide solid electrolyte may include lithium and sulfur, and may further include other elements, for example, may include but not limited to at least one of elements such as P, Si, Ge, Sn, Al.

[0069] Specifically, the general structural formula of the sulfide solid electrolyte can be expressed as yLi2S-(100-y)LS, wherein 0<y<100, and the LS may be, but not limited to, one or more of P2S5, SiS2, GeS2, SnS2, Al2S3 and other substances. The formed solid electrolyte system may include, but not limited to, one or more of a Li2S-P2S5 system, a Li2S-SiS2 system, a Li2S-GeS2 system, a Li2S-SnS2 system, and a Li2S-Al2S3 system. The state of the sulfide solid electrolyte may be crystalline, amorphous, or a crystalline-amorphous composite.

[0070] Further, the sulfide solid electrolyte may further include a doping material, and the doping material is preferably a lithium-containing compound LiQ. Specifically, the general structural formula of the doped sulfide electrolyte can be expressed as z(Li2S-LS)-(100-z)LiQ, wherein 90≤z≤100, and the doping material LiQ may include, but not limited to, a combination of one or more of lithium halide, lithium oxide, lithium nitride, lithium oxysalt and the like. Wherein, LiQ may include, but not limited to, LiF, LiCl, LiBr, LiI, Li2O, Li3N, LiAlO2, Li3PO4, Li2SO4, Li3BO3, Li4SiO4, LiN(SO2F)2, LiN(SO2RF)2, LiN(SO2F)(SO2RF) (substituent RF=C n nF 2n+1 2n+1, which is a saturated perfluoroalkyl group, and n is an integer of 1 to 2) and other one or more.

[0071] In some embodiments, the sulfide solid electrolyte comprises Li 10 10GeP2S 12 12, Li6PS5Cl, Li 10 10SnP2S 12 12, at least one of Li2S-P2S5, Li2S-SiS2 and Li2S-B2S3.

[0072] In some embodiments, the average particle size of the sulfide solid electrolyte is 0.5 μm to 5 μm. By way of example, the average particle size of the sulfide solid electrolyte is 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0073] The average particle size of the sulfide solid electrolyte refers to the average particle size of all sulfide solid electrolyte particles in the positive electrode sheet, and can be measured using methods and equipment known in the art. As an example, the following testing steps can be used: cut the positive electrode sheet into a sample of a certain size (e.g., 6mm × 6mm), observe the sulfide solid electrolyte particles on the electrode surface using a scanning electron microscope (e.g., ZEISS Sigma 300), and statistically analyze the particle size using ImageJ software. Perform this analysis 100 times, and fit the statistical data to a normal distribution curve to obtain the average particle size.

[0074] In some embodiments, based on the mass of the positive electrode film, the mass percentage of cellulose is 0.1% to 2%. As examples, the mass percentage of cellulose is 0.1%, 0.25%, 0.5%, 0.75%, 0.9%, 1%, 1.2%, 1.5%, 2%, etc.

[0075] Furthermore, based on the mass of the positive electrode film, the mass percentage of cellulose is 0.1% to 0.9%.

[0076] In some embodiments, the mass percentage of the sulfide solid electrolyte in the positive electrode film is 6% to 20%. As examples, the mass percentage of the sulfide solid electrolyte is 6%, 10%, 12%, 15%, 20%, etc.

[0077] Furthermore, based on the mass of the positive electrode film, the mass percentage of the sulfide solid electrolyte is 6% to 15%.

[0078] In some embodiments, the mass ratio of cellulose to sulfide solid electrolyte is 1:(5~60). As examples, the mass ratio of cellulose to sulfide solid electrolyte can be 1:5, 1:10, 1:15, 1:20, 1:30, 1:40, 1:50, 1:60, etc.

[0079] Furthermore, the mass ratio of cellulose to sulfide solid electrolyte is 1:(15~60).

[0080] In this application, the ionic conductivity of the positive electrode can be greater than 0.4 mS / cm.

[0081] The term "ionic conductivity" refers to the ability of the positive electrode to transport ions. The higher the ionic conductivity, the stronger the ability of the positive electrode to transport ions.

[0082] In some embodiments, the specific type of positive electrode active material is not particularly limited. As an example, the positive electrode active material may include at least one of the following materials: lithium 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 battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0083] In some embodiments, to further improve energy density, the positive electrode active material may include materials with the general formula Li. a Ni b Co c M d O e A fone or more of lithium transition metal oxides and modified compounds thereof, wherein 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.

[0084] In the present application, the modified compound of each positive electrode active material described above may be the positive electrode active material that is doped and / or surface-coated modified.

[0085] During charging and discharging of a battery, it is accompanied by deintercalation and consumption of Li. When the battery is discharged to different states, the molar content of Li is different. In the recitation of positive electrode materials in the present application, the molar content of Li refers to that in the initial state of the material, that is, the state before feeding. After the positive electrode material is applied to a battery system and undergoes charge-discharge cycles, the molar content of Li will change.

[0086] In the recitation of positive electrode active materials in the present application, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0087] In the battery cell of the present application, the specific type of the positive electrode current collector is not particularly limited. The positive electrode current collector can be a conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate or a composite current collector. The conductive carbon material of the conductive carbon sheet can be selected from one or more of Super P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene and carbon nanofibers. The metal materials of the metal foil, the carbon-coated metal foil and the porous metal plate are each independently selected from at least one of copper, aluminum, nickel and stainless steel. The composite current collector can be a composite current collector formed by compounding a metal foil and a polymer-based film.

[0088] In some embodiments, the positive electrode film layer may optionally further include a binder. By way of example, the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0089] In some embodiments, the positive electrode film layer may optionally further include a conductive agent. By way of example, the conductive agent can be selected from at least one of conductive carbon black (Super P), acetylene black, vapor-grown carbon fiber (abbreviated as VGCF), carbon nanotubes and graphene.

[0090] [Preparation method of positive electrode pole piece]

[0091] In this embodiment, the positive electrode sheet is prepared in the following manner:

[0092] S10: The mixture containing cellulose and sulfide solid electrolyte is dispersed and then dried to obtain a mixture. In this mixture, cellulose carries a negative charge.

[0093] In some embodiments, the cellulose carries a negative charge in the mixture. This can be achieved by simultaneously introducing modified groups into the cellulose during its preparation; alternatively, the cellulose can be modified after preparation, for example, by reacting the hydroxyl groups in the cellulose with acid anhydrides or acid anhydride compounds to form ester groups, or by treating the cellulose with 2,2,6,6-tetramethylpiperidine oxide (TEMPO) to introduce negatively charged carboxyl groups, or by sulfonating the cellulose to give it sulfonic acid groups on its surface. These groups ionize in the mixture, thus giving the cellulose a negative charge on its surface.

[0094] "Cellulose carries a negative charge in the mixture" means that after cellulose is dispersed in a solution, the groups on the surface of cellulose ionize in the solution, thus giving the cellulose surface a negative charge; it can also mean that cellulose itself carries a negative charge and remains so even when directly dispersed in a solution.

[0095] Those skilled in the art can use the zeta potential to test whether the groups on the surface of cellulose can ionize, thus giving cellulose a negative charge. As an example, cellulose is dispersed in deionized water to obtain a dispersion, and the dispersion is tested using a zeta potential meter. If the zeta potential is less than 0 mV, it indicates that the groups on the surface of cellulose carry a negative charge in water.

[0096] In other embodiments, the zeta potential of the mixture is -30mV to -80mV. As examples, the zeta potential of the mixture is -30mV, -40mV, -50mV, -60mV, -70mV, -80mV, etc.

[0097] By testing the Zeta potential of the mixture (a dispersion containing cellulose and sulfide electrolytes), it can be determined that the cellulose groups in the mixture carry a negative charge. In the dispersion containing cellulose and sulfide electrolytes, a small portion of the metal cations (e.g., lithium ions) in the sulfide electrolytes combine with the negative charge on the cellulose surface. However, most of the cellulose and sulfide electrolytes remain in the dispersion form. Therefore, when measuring the Zeta potential of the mixture, the negative charge of the cellulose can still be determined from the Zeta potential value. During the subsequent drying process, as the amount of solvent decreases, the negative charge on the cellulose surface induces the arrangement of the sulfide electrolytes, causing at least some of the solid sulfide electrolytes to be distributed along the extension direction of the cellulose, thus forming a bead-like structure.

[0098] In some embodiments, the mass ratio of cellulose to sulfide solid electrolyte in the mixture is 1:(5~60). As an example, the mass ratio of cellulose to sulfide solid electrolyte in the mixture can be 1:5, 1:10, 1:15, 1:20, 1:30, 1:40, 1:50, 1:60, etc.

[0099] In some embodiments, the solvent in the mixture is a nonpolar solvent or / and a weakly polar solvent to avoid reaction with the sulfide solid electrolyte.

[0100] Nonpolar solvents refer to solvents with low dielectric constants, also known as inert solvents, which do not undergo solvation reactions with the solute. For example, a nonpolar solvent can be at least one of n-heptane, toluene, n-hexane, xylene, n-butyl ether, anisole, or butyl butyrate. Weakly polar solvents refer to solvents with relatively weak polarity but still possessing certain polar characteristics, typically having a low dielectric constant. For example, a weakly polar solvent can be a carbonate or carboxylic acid ester, such as ethyl acetate or dimethyl carbonate. The solvent used in this application can be one or more of the above-mentioned solvents, without limitation, as long as it does not chemically react with the sulfide solid electrolyte.

[0101] In some embodiments, the solid content of the mixture is 50% to 80%. As an example, the solid content of the mixture can be 50%, 60%, 70%, 80%, etc.

[0102] The solid content refers to the percentage of solid components in the mixture. The higher the solid content, the higher the amount of cellulose and sulfide solid electrolytes used.

[0103] In some embodiments, the mixture dispersion step may be: first dispersing cellulose in a solvent, and then adding sulfide solid electrolyte for mixing and dispersion; or first dispersing sulfide solid electrolyte in a solvent, and then adding cellulose for further mixing and dispersion; or dispersing cellulose and sulfide solid electrolyte separately in a solvent, and then mixing and dispersing them together; or adding cellulose and sulfide solid electrolyte to the solvent simultaneously for dispersion.

[0104] In some embodiments, the mixture dispersion step is carried out in a shearing device or a homogenizing device, such as a high-pressure homogenizer, dispersion disc, sand mill, internal mixer, microfluidic homogenizer, etc., which is beneficial for fully and uniformly dispersing the cellulose and sulfide solid electrolytes. As an example, the mixture dispersion step is carried out in a high-pressure homogenizer, and the homogenization pressure can be 40 MPa for 1 hour.

[0105] In some embodiments, the drying method may be spray drying.

[0106] The spray drying temperature can be any temperature conventional for spray drying in this field. Further, the spray drying temperature is 200℃~250℃, and the drying time is 1s~2s.

[0107] In other embodiments, other drying methods may also be used, such as vacuum drying.

[0108] S20: The mixture is mixed with the positive electrode active material to form a positive electrode mixture. The positive electrode mixture is used to form a positive electrode film layer on the surface of the positive electrode current collector to obtain a positive electrode sheet.

[0109] In some embodiments, the mass percentage of cellulose in the cathode mixture is 0.1% to 2%. For example, the mass percentage of cellulose is 0.1%, 0.25%, 0.5%, 0.75%, 0.9%, 1%, 1.2%, 1.5%, 2%, etc.

[0110] Furthermore, based on the mass of the cathode mixture, the mass percentage of cellulose is 0.1% to 0.9%.

[0111] In some embodiments, the mass percentage of the sulfide solid electrolyte in the positive electrode mixture is 6% to 20%. As examples, the mass percentage of the sulfide solid electrolyte is 6%, 10%, 12%, 15%, 20%, etc.

[0112] Furthermore, based on the mass of the cathode mixture, the mass percentage of the sulfide solid electrolyte is 6% to 15%.

[0113] Understandably, those skilled in the art can obtain the positive electrode sheet using either dry or wet methods.

[0114] In some embodiments, the positive electrode sheet can be prepared by the following wet coating method: the positive active material, the mixture, the conductive agent and the binder are mixed in an organic solvent and dispersed to form a positive electrode mixture; the dispersed positive electrode mixture is uniformly coated on the surface of the positive current collector, dried, cold-pressed and cut to obtain the positive electrode sheet.

[0115] In the wet coating method, the organic solvent used must not react with the sulfide solid electrolyte and can be selected from at least one of the following: ether organic solvents, hydrocarbon organic solvents, ester organic solvents, nitrile organic solvents, amide organic solvents, alcohol organic solvents, and halogenated organic solvents. Specifically, the ether organic solvent is selected from at least one of diethyl ether, tetrahydrofuran, and ethylene glycol dimethyl ether; the hydrocarbon organic solvent is selected from at least one of n-pentane, n-hexane, cyclohexane, toluene, xylene, and trimethylbenzene; the ester organic solvent is selected from at least one of ethyl acetate, methyl formate, and dimethyl phthalate; the nitrile organic solvent is selected from acetonitrile; the amide organic solvent is selected from N-methylpyrrolidone (NMP) and / or N,N-dimethylformamide (DMF); the alcohol organic solvent is selected from ethanol; and the halogenated organic solvent is selected from dichloromethane and / or 1,2-dichloroethane.

[0116] In some embodiments, the positive electrode sheet can also be prepared by a dry pressing method as follows: The positive electrode active material, the mixture, and the conductive agent are dispersed and mixed in a certain proportion to form a positive electrode mixture; the positive electrode mixture is dispersed on the surface of the positive electrode current collector, and then hot-pressed into a film to obtain the positive electrode sheet. The dispersion process can be mechanical ball milling, etc. In other embodiments, the positive electrode mixture can be first pressed into a film, and then rolled and laminated onto the surface of the positive electrode current collector.

[0117] [Negative electrode plate]

[0118] The negative electrode includes a negative current collector and a layer of metallic lithium or a lithium alloy disposed on the negative current collector. The lithium alloy may include at least one of lithium-indium alloy, lithium-zinc alloy, lithium-magnesium alloy, lithium-tin alloy, and lithium-silver alloy. The thickness of the metallic lithium or lithium alloy layer can be 1 μm to 200 μm, preferably 5 μm to 100 μm.

[0119] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (sodium, sodium alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0120] The negative electrode sheet can be prepared by attaching metallic lithium or lithium alloy to the surface of the negative electrode current collector to form a negative electrode sheet.

[0121] [Solid electrolyte membrane]

[0122] In this embodiment, the solid electrolyte can also be selected from sulfide solid electrolytes, and the range of sulfide solid electrolytes is the same as that of solid electrolytes in the positive electrode.

[0123] In some embodiments, the solid electrolyte may be at least one of an oxide solid electrolyte, a polymer solid electrolyte, or a halide solid electrolyte.

[0124] Among them, the polymer solid electrolyte material (SPE) is composed of a polymer matrix (such as polyester, polyenzyme and polyamine) and a metal salt (such as LiClO4, LiAsF4, LiPF6, LiBF4, etc.). The polymer matrix can be selected from at least one of polyester, polyenzyme and polyamine, and the lithium salt can be selected from at least one of LiClO4, LiAsF4, LiPF6 and LiBF4.

[0125] Common SPEs include polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polypropylene oxide (PPO), polyvinylidene chloride (PVDC), and single-ion polymer electrolytes.

[0126] Furthermore, the polymer matrix can be hybridized with inorganic particles, including metal oxide nanoparticles such as MgO, Al2O3, and SiO2, as well as at least one of zeolite and montmorillonite. The addition of these inorganic particles disrupts the orderliness of the polymer chain segments in the matrix, reducing its crystallinity. The interactions between the polymer, lithium salt, and inorganic particles increase ion transport channels, improving conductivity and ion transference number. Inorganic fillers can also adsorb trace impurities (such as moisture) in the composite electrolyte and improve its mechanical properties.

[0127] Oxide solid electrolytes: Based on their material structure, oxide solid electrolytes can be divided into two categories: crystalline and glassy (amorphous). Crystalline electrolytes include perovskite, NASICON, LISICON, and garnet types, while glassy oxide electrolytes include LiPON type electrolytes. As an example, oxide solid electrolytes may include Li... 3.3 La 0.56 TiO3, LiTi2(PO4)3, Li 14 Zn(GeO4)4, Li7La3Zr2O 12 Li 1+x Al x Ti 2-x (PO4)3 (0 < x < 2), Li 7-a La3Zr 2-a MaO 12 (M=Ta, Nb; 0<a<2), Li b La2 / 3-b TiO3 (0 < b < 2), LiAlO2, Li2ZrO3 and Li4Ti5O 12 At least one of them.

[0128] Halide solid electrolytes are a class of solid compounds composed of halide ions (such as fluoride ions, chloride ions, etc.) and metal ions (such as lithium ions, sodium ions, etc.). As an example, halide solid electrolytes may include at least one of Li3YCl6, Li3ErCl6, Li3YBr6, Li3InBr6, or Li3InCl6.

[0129] Among them, solid electrolyte membranes can be prepared from solid electrolytes by dry membrane preparation or wet membrane preparation.

[0130] In some embodiments, the dry membrane formation method is as follows: a solid electrolyte is placed in a mold and pressed into a membrane. The pressing method can be cold pressing or hot pressing. The pressing method can be one-step pressing or multi-step pressing. The hot pressing pressure is 0.1 MPa to 500 MPa, preferably 100 MPa to 400 MPa; the hot pressing temperature is 25°C to 160°C, preferably 60°C to 120°C. If the hot pressing pressure is too low or the temperature is too low, the resulting solid electrolyte membrane will have low density; however, if the hot pressing pressure is too high, the equipment requirements will be high, and if the hot pressing temperature is too high, the solid electrolyte will easily decompose.

[0131] In some embodiments, the wet membrane fabrication method is as follows: a solid electrolyte and a binder are mixed in an organic solvent and dispersed into a slurry; the slurry is coated onto a glass substrate, dried, and then pressed to obtain a sulfide electrolyte membrane. The binder and organic solvent can be selected from the same range as those used in the wet coating method for preparing the positive electrode sheet.

[0132] In some embodiments, a single battery cell may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly comprising a positive electrode, a negative electrode, and a solid electrolyte membrane.

[0133] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0134] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 shows a square battery cell 5 as an example.

[0135] In some embodiments, referring to FIG3, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a solid electrolyte membrane may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0136] [Battery Module]

[0137] The battery cells of this application can be assembled into a battery module. The number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0138] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0139] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0140] Solid-state batteries

[0141] This application also provides a solid-state battery, including the above-mentioned battery cells. The number of battery cells in the solid-state battery can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity.

[0142] Solid-state batteries refer to batteries that use solid materials as electrolytes. Figures 4 and 5 show an example of a solid-state battery 1. Referring to Figures 5 and 6, the solid-state battery 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0143] It should be understood that in some embodiments, the solid-state battery 1 described above is also referred to as a battery pack. The individual battery cells 5 can be first assembled into a battery module 4, and the solid-state battery 1 is composed of the battery module 4. Alternatively, the solid-state battery 1 can be directly assembled from the individual battery cells 5, omitting the intermediate form of the battery module 4.

[0144] [Electrical appliances]

[0145] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or solid-state battery provided in this application. The battery cell, battery module, or solid-state battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0146] As an electrical device, you can choose individual battery cells, battery modules, or solid-state batteries according to your usage requirements.

[0147] Figure 7 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the battery cells in this device, batteries or battery modules can be used.

[0148] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0149] Example

[0150] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0151] Example 1

[0152] This embodiment provides a battery cell, the preparation method of which includes the following steps:

[0153] (1) Preparation of positive electrode sheet

[0154] Sulfonated modified ethyl cellulose (weight average molecular weight of 1 million, average diameter of 8 μm, average length of 1 mm, and average aspect ratio of 62.5) and Li6PS5Cl (hereinafter referred to as LPSC, average particle size of 4 μm) were mixed with butyl butyrate at a mass ratio of 0.5:14.5 to obtain a mixture with a solid content of 70%. The mixture was then dispersed using a high-pressure homogenizer at a homogenization pressure of 40 MPa for 1 h. The dispersed slurry was then spray-dried to obtain the final mixture.

[0155] LiNi, the positive electrode active material0.8 Co 0.1 Mn 0.1 O2 (hereinafter referred to as NCM811), the above mixture, conductive agent VGCF, and binder PVDF are added to ethyl acetate in a weight ratio of 80:15:3:2, with the solid content controlled at 70%. After thorough stirring and mixing, the mixture is coated on aluminum foil to obtain a positive electrode sheet with a thickness of 80μm.

[0156] (2) Preparation of negative electrode sheet

[0157] A 25μm thick lithium metal sheet is attached to the surface of a copper foil, sliced, and the negative electrode is obtained.

[0158] (3) Solid electrolyte membrane

[0159] In a glove box, the sulfide solid electrolyte LPSC was pressed at 100℃ and 250MPa for 2 min to obtain a solid electrolyte membrane with a thickness of 50μm.

[0160] (4) Battery cell

[0161] The positive electrode, solid electrolyte membrane, and negative electrode are aligned and stacked in sequence. They are then cold-pressed at room temperature and 250 MPa for 2 minutes to obtain a cell unit. The single-layer cell unit is then cold-pressed and placed in an outer packaging to form a battery cell.

[0162] The positive electrode sheet prepared in Example 1 was subjected to transmission electron microscopy (TEM) testing. Figure 8 shows a TEM cross-sectional view of the positive electrode sheet in Example 1 of this application. As can be seen from Figure 8, the particulate sulfide solid electrolyte (LPSC) is arranged in an orderly manner along the extension direction of cellulose, forming a "beaded" structure with the cellulose backbone (CNF backbone). Part of the cellulose is wrapped around the positive electrode active material (NCM) and in contact with a portion of the surface of the positive electrode active material. The cellulose surrounding the positive electrode active material and the sulfide solid electrolyte arranged on the cellulose surface provide a certain degree of constraint to the positive electrode active material.

[0163] Example 2

[0164] The difference between Example 2 and Example 1 is that the mass ratio of sulfonated modified ethyl cellulose to sulfide solid electrolyte LPSC in step (1) is 0.25:14.75.

[0165] Example 3

[0166] The difference between Example 3 and Example 1 is that the mass ratio of sulfonated modified ethyl cellulose to sulfide solid electrolyte LPSC in step (1) is 0.75:14.25.

[0167] Example 4

[0168] The difference between Example 4 and Example 1 is that the mass ratio of sulfonated modified ethyl cellulose to sulfide solid electrolyte LPSC in step (1) is 1:14.

[0169] Example 5

[0170] The difference between Example 5 and Example 1 is that in step (1), the sulfonated modified ethyl cellulose in Example 1 is replaced with sulfonated modified methyl cellulose.

[0171] Example 6

[0172] The difference between Example 6 and Example 1 is that in step (1), the sulfonated modified ethyl cellulose in Example 1 is replaced with sulfonated modified cyano cellulose.

[0173] Example 7

[0174] The difference between Example 7 and Example 1 is that in step (1), the sulfide solid electrolyte LPSC of Example 1 is replaced with Li3PS4.

[0175] Example 8

[0176] The difference between Example 8 and Example 1 is that the sulfonated modified ethyl cellulose in step (1) has a molecular weight of 1.5 million, an average diameter of 10 μm, an average length of 2 mm, and an average aspect ratio of 200.

[0177] Example 9

[0178] The difference between Example 9 and Example 1 is that the average particle size of the sulfide solid electrolyte LPSC in step (1) is 2.8 μm.

[0179] Comparative Example 1

[0180] The difference between Comparative Example 1 and Example 1 is that step (1) includes replacing the sulfonated modified ethyl cellulose of Example 1 with ethyl cellulose in step (1).

[0181] Comparative Example 2

[0182] The difference between Comparative Example 2 and Example 1 is that cellulose was not added in step (1).

[0183] Comparative Example 3

[0184] The difference between Comparative Example 3 and Example 6 is that cellulose was not added in step (1).

[0185] Comparative Example 4

[0186] The difference between Comparative Example 4 and Example 1 is that step (1) includes: sulfonated modified ethyl cellulose (weight average molecular weight of 1 million, average diameter of 8 μm, average length of 1 mm, average aspect ratio of 62.5) and Li6PS5Cl (average particle size of 4 μm) are mixed with butyl butyrate at a mass ratio of 0.5:14.5, and then dispersed using a high-pressure homogenizer at a homogenization pressure of 40 MPa for 1 h to obtain a mixed solution. The positive electrode active material NCM811, conductive agent VGCF, and binder PVDF are added to the above mixed solution, with the solid content controlled at 70%. The mass ratio of the positive electrode active material NCM811, conductive agent VGCF, binder PVDF, and the total mass of sulfonated modified ethyl cellulose and Li6PS5Cl is 80:3:2:15. After thorough mixing, the mixture is coated onto aluminum foil to obtain a positive electrode sheet with a thickness of 80 μm.

[0187] Table 1 shows some of the preparation parameters of the positive electrode sheets in Examples 1 to 9 and Comparative Examples 1 to 4.

[0188] Table 1. Some preparation parameters of the positive electrode sheet in the examples and comparative examples.

[0189]

[0190] Performance testing

[0191] The positive electrode sheets and battery cells prepared in the examples and comparative examples were subjected to performance tests, and the test methods are as follows:

[0192] 1. Positive electrode sheet

[0193] Ionic conductivity: Assemble the positive electrode into a single-layer symmetrical cell, add electrolyte and LiIn to each side, and 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 in the EIS. Electrode ionic conductivity = d (electrode thickness) / (Rion * A (electrode area)).

[0194] 2. Battery cell

[0195] The charging and discharging operating voltage range was set to 2.5V~4.25V, and cyclic testing was conducted using a constant current charging and discharging method. The test current was 0.1C (current density approximately 0.12mA / cm²). 2 The test temperature was 25℃.

[0196] (1) First week discharge specific capacity: The first week discharge specific capacity of the battery was tested at a charge and discharge current of 0.1C.

[0197] (2) First-time effect: The battery's first-time effect is tested at a charge-discharge current of 0.1C. The battery's first-time effect = first-week discharge specific capacity / first-week charge specific capacity × 100%.

[0198] (3) Capacity retention rate: After cycling the battery for 200 cycles, test the discharge specific capacity after 200 cycles and calculate the capacity retention rate. Capacity retention rate = discharge specific capacity after 200 cycles / discharge specific capacity in the first cycle × 100%.

[0199] The performance test results are shown in Table 2.

[0200] Table 2 Performance test results of individual cells in the examples and comparative examples

[0201]

[0202] As can be seen from Tables 1 and 2, compared with Comparative Examples 1 to 4, the positive electrode sheets in Examples 1 to 9 all exhibit higher ionic conductivity, meaning better ion transport performance. This results in higher first-cycle discharge specific capacity and first-cycle efficiency for the corresponding battery cells, as well as good cycle performance. Specifically, the ionic conductivity of the positive electrode sheet is not less than 0.36 mS / cm, and can reach as high as 0.44 mS / cm; the first-cycle discharge specific capacity of the battery cells is not less than 176 mAh / g, and can reach as high as 180 mAh / g; the first-cycle efficiency is not less than 84%, and can reach as high as 87%; and after 200 cycles, the capacity retention rate of the battery cells is not less than 87%, and can reach as high as 89%.

[0203] Comparing the performance test results of Example 1 and Comparative Examples 1-2, as well as Example 6 and Comparative Example 3, it can be seen that by adding sulfonated modified cellulose to the positive electrode film layer and separately dispersing the sulfonated modified cellulose and sulfide solid electrolyte to form a "beaded" structure, the ion transport of the positive electrode sheet can be effectively improved, thereby increasing the first-cycle discharge specific capacity and first-cycle efficiency of the battery cell and improving cycle performance.

[0204] Comparing the performance test results of Example 1 and Comparative Example 4, it can be seen that when sulfonated modified cellulose and sulfide solid electrolyte are directly mixed with positive electrode active material, the ionic conductivity of the positive electrode sheet is significantly reduced, the first-cycle discharge specific capacity and first-cycle efficiency of the corresponding battery cell are also significantly reduced, and the cycle performance is also significantly worse.

[0205] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, The device includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer attached to the surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, a sulfide solid electrolyte, and cellulose. At least a portion of the sulfide solid electrolyte is distributed along the extension direction of the cellulose, and at least a portion of the cellulose is in contact with a portion of the surface of the positive electrode active material.

2. The battery cell as described in claim 1, characterized in that, The sulfide solid electrolyte, comprising ≥30% of the total amount, is distributed along the extension direction of the cellulose.

3. The battery cell as described in claim 1 or 2, characterized in that, The cellulose includes sulfonated modified cellulose; And / or, the cellulose includes at least one of sulfonated modified ethyl cellulose, sulfonated modified methyl cellulose, or sulfonated modified cyanocellulose; And / or, the weight-average molecular weight of the cellulose is 50,000 to 2,500,000; And / or, the average length of the cellulose is 0.2 mm to 20 mm, and the average diameter is 5 μm to 20 μm; And / or, the average aspect ratio of the cellulose is 20 to 2000.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The average particle size of the sulfide solid electrolyte is 0.5 μm to 5 μm.

5. The battery cell according to any one of claims 1 to 4, characterized in that, Based on the mass of the positive electrode film, the mass percentage of cellulose is 0.1% to 2%. And / or, based on the mass of the positive electrode film, the mass percentage of the sulfide solid electrolyte is 6% to 20%; And / or, the mass ratio of the cellulose to the sulfide solid electrolyte is 1:(5~60).

6. The battery cell as described in claim 5, characterized in that, Based on the mass of the positive electrode film, the mass percentage of cellulose is 0.1% to 0.9%. And / or, based on the mass of the positive electrode film, the mass percentage of the sulfide solid electrolyte is 6% to 15%; And / or, the mass ratio of the cellulose to the sulfide solid electrolyte is 1:(15~60).

7. A method for preparing a single battery cell, characterized in that, Includes the following steps: A mixture containing cellulose and sulfide solid electrolyte is dispersed and then dried to obtain a mixture; wherein the cellulose in the mixture carries a negative charge; The mixture is mixed with a positive electrode active material to form a positive electrode mixture, and the positive electrode mixture is used to form a positive electrode film on the surface of a positive electrode current collector to obtain a positive electrode sheet. The positive electrode, negative electrode, and solid electrolyte membrane are assembled to obtain a single battery cell.

8. The preparation method according to claim 7, characterized in that, The solid content of the mixture is 50% to 80%.

9. The preparation method according to claim 7 or 8, characterized in that, The zeta potential of the mixture is -30mV to -80mV; And / or, the cellulose includes sulfonated modified cellulose; And / or, the cellulose includes at least one of sulfonated modified ethyl cellulose, sulfonated modified methyl cellulose, or sulfonated modified cyanocellulose; And / or, the weight-average molecular weight of the cellulose is 50,000 to 2,500,000; And / or, the average length of the cellulose is 0.2 mm to 20 mm, and the average diameter is 5 μm to 20 μm; And / or, the average aspect ratio of the cellulose is 20 to 2000.

10. The preparation method according to any one of claims 7 to 9, characterized in that, The average particle size of the sulfide solid electrolyte is 0.5 μm to 5 μm.

11. The preparation method according to any one of claims 7 to 10, characterized in that, In the mixture, the mass ratio of the cellulose to the sulfide solid electrolyte is 1:(5~60); And / or, based on the mass of the positive electrode mixture, the mass percentage of cellulose is 0.1% to 2%; And / or, based on the mass of the positive electrode mixture, the mass percentage of the sulfide solid electrolyte is 6% to 20%.

12. A solid-state battery, characterized in that, It includes battery cells as described in any one of claims 1 to 6, or battery cells prepared by the preparation method as described in any one of claims 7 to 11.

13. An electrical appliance, characterized in that, Including the solid-state battery as described in claim 12.

Images