Secondary battery, electric device, solid electrolyte layer and preparation method therefor

Abstract

Provided are a secondary battery, an electric device, a solid electrolyte layer and a preparation method therefor. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a solid electrolyte layer located between the positive electrode sheet and the negative electrode sheet. The solid electrolyte layer comprises an electrolyte material, a first binder, and a second binder. The first binder includes a polydiene-based binder, and the second binder includes a cellulose-based binder.

Description

Secondary batteries, electrical devices, solid electrolyte layers and their preparation methods

[0001] Cross-reference to related applications

[0002] This disclosure is based on and claims priority to Chinese Patent Application No. 202411203295.2, filed on August 29, 2024, entitled "Secondary Battery, Electrical Device, Solid Electrolyte Layer and Preparation Method Thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, and in particular to a secondary battery, an electrical device, a solid electrolyte layer, and a method for preparing the same. Background Technology

[0004] In recent years, with the increasingly wide application of secondary batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and many other fields. Due to the significant development of secondary batteries, higher requirements have been placed on their initial coulombic efficiency and cycle performance. Summary of the Invention

[0005] This disclosure is made in view of the above-mentioned problems, and its object is to provide a secondary battery, an electrical device, a solid electrolyte layer, and a method for preparing the same. The secondary battery of this disclosure has improved initial coulombic efficiency and cycle performance.

[0006] To achieve the above objectives, the first aspect of this disclosure provides a secondary battery, including a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode; the solid electrolyte layer includes an electrolyte material, a first binder, and a second binder; the first binder includes a polydiolefin binder, and the second binder includes a cellulose binder.

[0007] In this disclosure, the solid electrolyte layer of the secondary battery comprises a polydiolefin binder and a cellulose binder. The polydiolefin binder has non-polar segments that interact weakly with the electrolyte material and are stably dispersed in a non-polar solvent. This prevents the electrolyte material from agglomerating or settling, improving the uniformity of electrolyte material distribution in the solid electrolyte layer. Consequently, the lithium-ion transport pathway is uniform, resulting in higher lithium-ion transport efficiency and thus improving the initial coulombic efficiency of the secondary battery. Furthermore, the more uniform distribution of electrolyte material in the solid electrolyte layer reduces lithium plating, improving the cycle performance of the secondary battery. In addition, the polar groups of the cellulose binder interact strongly with the electrolyte material, allowing them to bind well to the surface of the electrolyte material. This improves the film stability of the solid electrolyte layer, further enhancing the cycle performance of the secondary battery.

[0008] In some embodiments, the total mass percentage of the first binder and the second binder in the solid electrolyte layer is 0.1% to 9.1%. This is beneficial for improving the ionic conductivity of the solid electrolyte layer, thereby improving the lithium-ion transport rate in the secondary battery, and consequently improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0009] In some embodiments, the total mass percentage of the first binder and the second binder in the solid electrolyte layer is 0.1% to 1.5%. This is more conducive to improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0010] In some embodiments, the mass ratio of the first binder to the second binder is 1:5 to 10:1. In other embodiments, the mass ratio of the first binder to the second binder is 2:1 to 5:1. This improves both the uniformity of electrolyte material distribution in the solid electrolyte layer and the stability of the solid electrolyte layer, thus enhancing the initial coulombic efficiency and cycle performance of the secondary battery.

[0011] In some embodiments, the first adhesive comprises structural units derived from the monomer shown in Formula 1 and structural units derived from the monomer shown in Formula 2:

[0012] Among them, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, and R15 are each independently one of hydrogen, C1 to C20 alkyl, or C6 to C20 aryl.

[0013] In some embodiments, the first binder includes one or more of poly(2,3-dimethyl-1,3-butadiene), polybutadiene, polyisoprene, polyhexadiene, natural rubber, styrene-butadiene rubber, hydrogenated polybutadiene, hydrogenated polyisoprene, and hydrogenated natural rubber. In some embodiments, the first binder includes poly(2,3-dimethyl-1,3-butadiene). Using the above-mentioned first binder is beneficial for improving the uniformity of electrolyte material distribution in the solid electrolyte layer, thereby improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0014] In some embodiments, the number average molecular weight of the first binder is between 50,000 and 5 million. This is beneficial for improving the uniformity of electrolyte material distribution in the solid electrolyte layer.

[0015] In some embodiments, the second adhesive comprises a compound shown in Formula 3:

[0016] R1, R2, and R3 are each independently one of C1-C20 alkyl, C6-C20 aryl, hydroxyethyl, and cyanoethyl; n is greater than or equal to 50.

[0017] In some embodiments, the second binder includes one or more of methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cyanoethylcellulose, methylhydroxyethylcellulose, and ethylhydroxyethylcellulose. In some embodiments, the second binder includes ethylcellulose. Using the above-mentioned second binder is beneficial to improving the stability of the solid electrolyte membrane layer, thereby improving the cycle performance of the secondary battery.

[0018] In some embodiments, the number-average molecular weight of the second binder is between 30,000 and 3 million. This facilitates the bonding between electrolyte materials and between the solid electrolyte layer and the negative and positive electrode sheets.

[0019] In some embodiments, the electrolyte material includes one or more of sulfide electrolyte materials, oxide electrolyte materials, and polymer electrolyte materials. This improves the conductivity of the solid electrolyte film, thereby benefiting the initial coulombic efficiency and cycle performance of the secondary battery.

[0020] In some embodiments, the electrolyte material accounts for 88.9% to 99.9% of the mass of the solid electrolyte layer. Therefore, the electrolyte layer exhibits good lithium-ion conductivity.

[0021] In some embodiments, the solid electrolyte layer further includes a dispersant; the dispersant accounts for 0.05% to 2% of the mass of the solid electrolyte layer. This is beneficial to the uniform dispersion of the solid electrolyte material.

[0022] In some implementations, the secondary battery includes a solid-state battery.

[0023] A second aspect of this disclosure provides an electrical device including a secondary battery as described in the first aspect.

[0024] A third aspect of this disclosure provides a solid electrolyte layer, including an electrolyte material, a first binder, and a second binder; the first binder includes a polydiolefin binder, and the second binder includes a cellulose binder.

[0025] In this disclosure, the solid electrolyte layer comprises a polydiolefin binder and a cellulose binder. The polydiolefin binder has non-polar segments that interact weakly with the electrolyte material and are stably dispersed in a non-polar solvent. This prevents the electrolyte material from agglomerating or settling, improving the uniformity of electrolyte material distribution in the solid electrolyte layer. Consequently, the lithium-ion transport pathway is uniform, resulting in higher lithium-ion transport efficiency and thus improving the initial coulombic efficiency of the secondary battery. Furthermore, the more uniform distribution of electrolyte material in the solid electrolyte layer reduces lithium plating in the secondary battery, improving its cycle performance. In addition, the polar groups of the cellulose binder interact strongly with the electrolyte material, binding well to its surface and enhancing the stability of the solid electrolyte layer, further improving the cycle performance of the secondary battery.

[0026] In some embodiments, the total mass percentage of the first binder and the second binder in the solid electrolyte layer is 0.1% to 9.1%. This is beneficial for improving the ionic conductivity of the solid electrolyte layer, thereby improving the lithium-ion transport rate in the secondary battery, and consequently improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0027] In some embodiments, the mass ratio of the first binder to the second binder is 1:5 to 10:1. This improves both the uniformity of electrolyte material distribution in the solid electrolyte layer and the stability of the solid electrolyte layer, thus enhancing the initial coulombic efficiency and cycle performance of the secondary battery.

[0028] In some embodiments, the first adhesive comprises structural units derived from the monomer shown in Formula 1 and structural units derived from the monomer shown in Formula 2:

[0029] Among them, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, and R15 are each independently one of hydrogen, C1 to C20 alkyl, or C6 to C20 aryl.

[0030] In some embodiments, the first binder includes one or more of poly(2,3-dimethyl-1,3-butadiene), polybutadiene, polyisoprene, polyhexadiene, natural rubber, styrene-butadiene rubber, hydrogenated polybutadiene, hydrogenated polyisoprene, and hydrogenated natural rubber. Using the above-mentioned first binder helps improve the uniformity of electrolyte material distribution in the solid electrolyte layer, thereby improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0031] In some embodiments, the number average molecular weight of the first binder is between 50,000 and 5 million. This is beneficial for improving the uniformity of electrolyte material distribution in the solid electrolyte layer.

[0032] In some embodiments, the second adhesive comprises a compound shown in Formula 3:

[0033] R1, R2, and R3 are each independently one of C1-C20 alkyl, C6-C20 aryl, hydroxyethyl, and cyanoethyl; n is greater than or equal to 50.

[0034] In some embodiments, the second binder includes one or more of methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cyanoethylcellulose, methylhydroxyethylcellulose, and ethylhydroxyethylcellulose. This improves the stability of the solid electrolyte membrane, thereby enhancing the cycle performance of the secondary battery.

[0035] In some embodiments, the number-average molecular weight of the second binder is between 30,000 and 3 million. This facilitates the bonding between electrolyte materials and between the solid electrolyte layer and the negative and positive electrode sheets.

[0036] In some embodiments, the electrolyte material includes one or more of sulfide electrolyte materials, oxide electrolyte materials, and polymer electrolyte materials. Using the above-mentioned electrolyte materials can improve the conductivity of the solid electrolyte film, thereby benefiting the initial coulombic efficiency and cycle performance of the secondary battery.

[0037] The fourth aspect of this disclosure provides a method for preparing a solid electrolyte layer, comprising the following steps: a formulation step, comprising dissolving an electrolyte material, a first binder, and a second binder in a nonpolar solvent to form a solid electrolyte slurry; wherein the first binder includes a polydiolefin binder, and the second binder includes a cellulose binder; and a coating step, comprising coating the solid electrolyte slurry to form a solid electrolyte layer.

[0038] In this disclosure, a polydiolefin binder and a non-polar solvent are used in combination when preparing the solid electrolyte slurry. Because the polydiolefin binder can be dispersed uniformly in the non-polar solvent for a long time, and the non-polar segments in the polydiolefin binder can interact with the electrolyte material with weak forces to stably disperse in the non-polar solvent, the electrolyte material does not agglomerate or settle. Therefore, continuous stirring of the solid electrolyte slurry is not required before coating, reducing energy consumption and preventing the introduction of air bubbles, which is beneficial to the processing performance, initial coulombic efficiency, and cycle performance of the secondary battery. In addition, a cellulose binder is also used in the preparation of the solid electrolyte slurry. Cellulose binders have polar groups that interact strongly with the electrolyte material, allowing them to bind well to the surface of the electrolyte material, thereby improving the stability of the solid electrolyte layer. The solid electrolyte layer prepared by this disclosure has high film stability and uniform electrolyte material distribution, which is beneficial to the initial coulombic efficiency and cycle performance of the secondary battery.

[0039] In some embodiments, the total content of the first binder and the second binder in the solid electrolyte slurry is 0.1% to 9.1% based on the total weight of solids in the solid electrolyte slurry. This is beneficial for improving the ionic conductivity of the solid electrolyte layer, thereby improving the lithium-ion transport rate in the secondary battery, and consequently improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0040] In some embodiments, the mass ratio of the first binder to the second binder in the solid electrolyte slurry is 1:5 to 10:1, based on the total weight of solids in the solid electrolyte slurry. This improves both the uniformity of electrolyte material distribution in the solid electrolyte layer and the stability of the solid electrolyte layer, which is beneficial for improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0041] In some embodiments, the first adhesive comprises structural units derived from the monomer shown in Formula 1 and structural units derived from the monomer shown in Formula 2:

[0042] Among them, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, and R15 are each independently one of hydrogen, C1 to C20 alkyl, or C6 to C20 aryl.

[0043] In some embodiments, the first binder includes one or more of poly(2,3-dimethyl-1,3-butadiene), polybutadiene, polyisoprene, polyhexadiene, natural rubber, styrene-butadiene rubber, hydrogenated polybutadiene, hydrogenated polyisoprene, and hydrogenated natural rubber. Using the above-mentioned first binder helps improve the uniformity of electrolyte material distribution in the solid electrolyte layer, thereby improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0044] In some embodiments, the number average molecular weight of the first binder is between 50,000 and 5 million. This is beneficial for improving the uniformity of electrolyte material distribution in the solid electrolyte layer.

[0045] In some embodiments, the second adhesive comprises a compound shown in Formula 3:

[0046] R1, R2, and R3 are each independently one of C1-C20 alkyl, C6-C20 aryl, hydroxyethyl, and cyanoethyl; n is greater than or equal to 50.

[0047] In some embodiments, the second binder includes one or more of methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cyanoethylcellulose, methylhydroxyethylcellulose, and ethylhydroxyethylcellulose. This improves the stability of the solid electrolyte membrane, thereby enhancing the cycle performance of the secondary battery.

[0048] In some embodiments, the number-average molecular weight of the second binder is between 30,000 and 3 million. This facilitates the bonding between electrolyte materials and between the solid electrolyte layer and the negative and positive electrode sheets.

[0049] In some embodiments, the nonpolar solvent includes one or more of toluene, xylene, trimethylbenzene, heptane, octane, nonane, decane, undecane, dodecane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cyclododecane, and decahydronaphthalene. The first binder in the aforementioned electrolyte slurry can be dispersed uniformly in the nonpolar solvent for a long time, improving the dispersion uniformity of the electrolyte material in the electrolyte slurry, thereby improving the uniformity of the solid electrolyte layer, and consequently benefiting the initial coulombic efficiency and cycle performance of the secondary battery. Attached Figure Description

[0050] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0051] Figure 2 is an exploded view of a battery cell according to an embodiment of the present disclosure shown in Figure 1.

[0052] Figure 3 is a schematic diagram of a battery module according to one embodiment of the present disclosure.

[0053] Figure 4 is a schematic diagram of a battery pack according to one embodiment of the present disclosure.

[0054] Figure 5 is an exploded view of a battery pack according to an embodiment of the present disclosure, as shown in Figure 4.

[0055] Figure 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0056] Figure 7 is a schematic diagram of the structure of the solid electrolyte slurry in Embodiment 1 of this disclosure after standing for 12 hours.

[0057] Figure 8 is a schematic diagram of the structure of the solid electrolyte slurry in Comparative Example 1 of this disclosure after standing for 12 hours.

[0058] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0059] The following detailed description, with appropriate reference to the accompanying drawings, provides a specific embodiment of the secondary battery, power-consuming device, solid electrolyte layer, and method for preparing the present disclosure. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter of the claims.

[0060] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​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 disclosure, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0062] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0063] Unless otherwise specified, the terminology used in this disclosure has the common meaning as commonly understood by those skilled in the art.

[0064] Unless otherwise specified, the values ​​of the parameters mentioned in this disclosure can be determined using various test methods commonly used in the art, for example, according to the test methods given in this disclosure.

[0065] When manufacturing secondary batteries using a wet process, the electrolyte slurry is prone to sedimentation during the settling process, resulting in uneven distribution of the electrolyte slurry. This ultimately leads to uneven distribution of the electrolyte active material in the coated electrolyte membrane layer, causing uneven lithium-ion transport paths and lower lithium-ion transport efficiency, thus affecting the initial coulombic efficiency of the secondary battery. Furthermore, uneven distribution of the electrolyte active material in the electrolyte membrane layer can also result in excessively high local lithium-ion concentrations, causing lithium plating and affecting the cycle performance of the secondary battery.

[0066] In related technologies, the electrolyte slurry is typically continuously stirred before coating to prevent sedimentation of the electrolyte material and improve the uniformity of the formed electrolyte film. However, continuous stirring of the electrolyte slurry easily introduces air bubbles. On the one hand, these bubbles burst during coating, resulting in an uneven surface of the electrolyte film and affecting the uniformity of electrolyte material distribution. On the other hand, air bubbles occupy part of the space in the electrolyte film, also contributing to uneven distribution of the electrolyte material. Therefore, the effect of continuous stirring in related technologies on improving the uniformity of electrolyte active material distribution in the electrolyte film is not significant. Furthermore, the method of continuously stirring the electrolyte slurry places high demands on the production line process, requiring "stirring and coating simultaneously," resulting in high energy consumption.

[0067] Based on this, this disclosure provides a novel secondary battery, its preparation method, an electrical device, and a solid electrolyte layer. The secondary battery provided by this disclosure has improved initial coulombic efficiency and cycle performance.

[0068] Secondary batteries

[0069] The first aspect of this disclosure provides a secondary battery, including a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode; the solid electrolyte layer includes an electrolyte material, a first binder, and a second binder; the first binder includes a polydiolefin binder, and the second binder includes a cellulose binder.

[0070] In this disclosure, the solid electrolyte layer of the secondary battery comprises a polydiolefin binder and a cellulose binder. The polydiolefin binder has non-polar segments that interact weakly with the electrolyte material and are stably dispersed in a non-polar solvent. This prevents the electrolyte material from agglomerating or settling, improving the uniformity of electrolyte material distribution in the solid electrolyte layer. Consequently, the lithium-ion transport pathway is uniform, resulting in higher lithium-ion transport efficiency and thus improving the initial coulombic efficiency of the secondary battery. Furthermore, the more uniform distribution of electrolyte material in the solid electrolyte layer reduces lithium plating, improving the cycle performance of the secondary battery. In addition, the polar groups of the cellulose binder interact strongly with the electrolyte material, allowing them to bind well to the surface of the electrolyte material. This improves the film stability of the solid electrolyte layer, further enhancing the cycle performance of the secondary battery.

[0071] In some embodiments, the total mass percentage of the first binder and the second binder in the solid electrolyte layer is from 0.1% to 9.1%, optionally from 0.1% to 1.5%. A mass percentage of the first binder and the second binder in the solid electrolyte layer within the above range is beneficial for improving the ionic conductivity of the solid electrolyte layer, thereby improving the lithium-ion transport rate in the secondary battery, and consequently improving the initial coulombic efficiency and cycle performance of the secondary battery. Exemplarily, the mass percentage of the first binder and the second binder in the solid electrolyte layer is 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 8.5%, 9.1%, or a value within a range consisting of any two of these values.

[0072] In some embodiments, the mass ratio of the first binder to the second binder is from 1:5 to 10:1, optionally from 2:1 to 5:1. A mass ratio of the first binder to the second binder within the above range can improve the uniformity of electrolyte material distribution in the solid electrolyte layer while simultaneously improving the film stability of the solid electrolyte layer, which is beneficial for improving the initial coulombic efficiency and cycle performance of the secondary battery. Exemplarily, the mass ratio of the first binder to the second binder is 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or a value within a range consisting of any two of these values.

[0073] In some embodiments, the first adhesive comprises structural units derived from the monomer shown in Formula 1 and structural units derived from the monomer shown in Formula 2:

[0074] Among them, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, and R15 are each independently one of hydrogen, C1 to C20 alkyl, or C6 to C20 aryl.

[0075] In this disclosure, alkyl refers to an alkyl group having the general formula C2. n H 2n+1 A monovalent group is a group formed by removing one hydrogen atom from a saturated, straight-chain or branched aliphatic hydrocarbon. C1-C20 alkyl groups refer to straight-chain or branched alkyl groups having 1 to 20 carbon atoms. Examples of C1-C20 alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, 2-methylhexyl, heptyl, 2-methylheptyl, octyl, nonyl, decyl, undecyl, and dodecyl, which are straight-chain or branched alkyl groups having 1 to 20 carbon atoms.

[0076] In this disclosure, aryl refers to the collective term for a monovalent group remaining after removing a hydrogen atom from the aromatic carbon atom of an aromatic compound molecule. C6-C20 aryl refers to an aryl group having 6 to 20 carbon atoms. In some embodiments, the number of carbon atoms in the aryl group is C6-C12, optionally C6-C10. In some embodiments, the aryl group can be a monocyclic aryl, polycyclic aryl, or fused-ring aryl. A monocyclic aryl refers to an aryl group with only one aromatic ring in the molecule, such as phenyl, benzyl, phenethyl, etc.; a polycyclic aryl refers to an aryl group containing two or more independent aromatic rings in the molecule, such as biphenyl, terphenyl, etc.; a fused-ring aryl refers to an aryl group containing two or more aromatic rings fused together by sharing two adjacent carbon atoms, such as naphthyl, anthracene, phenanthryl, fluorene, benzo[a]fluorene, pyrene, triphenylene, fluoranyl, spirodifluorene, etc.

[0077] In some embodiments, the first binder includes one or more of poly(2,3-dimethyl-1,3-butadiene), polybutadiene, polyisoprene, polyhexadiene, natural rubber, styrene-butadiene rubber, hydrogenated polybutadiene, hydrogenated polyisoprene, and hydrogenated natural rubber; optionally, the first binder includes poly(2,3-dimethyl-1,3-butadiene). The aforementioned first binder has non-polar segments and flexibility, and these non-polar segments can interact with the electrolyte material with weak forces. This prevents the electrolyte material from agglomerating or settling. Therefore, using the aforementioned first binder is beneficial for improving the uniformity of electrolyte material distribution in the solid electrolyte layer, thereby improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0078] In some embodiments, the number-average molecular weight of the first binder is between 50,000 and 5,000,000, optionally between 500,000 and 2,000,000. A number-average molecular weight within this range is beneficial for improving the uniformity of electrolyte material distribution in the solid electrolyte layer. Exemplarily, the number-average molecular weight of the first binder can be 50,000, 500,000, 1,500,000, 2,000,000, 3,000,000, 4,000,000, 5,000,000, or a value within a range consisting of any two of these values.

[0079] In some embodiments, the structural formula of the cellulose binder is shown in Formula 3:

[0080] R1, R2, and R3 are each independently one of C1-C20 alkyl, C6-C20 aryl, hydroxyethyl, and cyanoethyl; n is greater than or equal to 50.

[0081] Here, alkyl groups of C1 to C20 and aryl groups of C6 to C20 have the same definitions as in Formulas 1 and 2 above, and will not be repeated here.

[0082] In some implementations, n is greater than or equal to 100. For example, n can be 200, 500, 1000, or 3000.

[0083] In some embodiments, the second binder includes one or more of methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cyanoethylcellulose, methylhydroxyethylcellulose, and ethylhydroxyethylcellulose; optionally, the second binder includes ethylcellulose. The above-mentioned second binder has good solubility and stable viscosity and adhesion. By using the above-mentioned second binder, it is beneficial to improve the stability of the solid electrolyte membrane layer, thereby improving the cycle performance of the secondary battery.

[0084] In some embodiments, the number-average molecular weight of the second binder is between 30,000 and 3,000,000, optionally between 500,000 and 2,000,000. A number-average molecular weight within this range is beneficial for the adhesion between electrolyte materials and for the adhesion between the solid electrolyte layer and the negative and positive electrode sheets. Exemplarily, the number-average molecular weight of the second binder can be 30,000, 500,000, 1,500,000, 2,000,000, 2,500,000, 3,000,000, or a value within a range of any two of these values.

[0085] In some embodiments, the electrolyte material includes one or more of sulfide electrolyte materials, oxide electrolyte materials, and polymer electrolyte materials. In some embodiments, the aforementioned sulfide electrolyte material includes one or more of lithium phosphorus-containing sulfide electrolyte materials, lithium chloride-containing sulfide electrolyte materials, lithium bromide-containing sulfide electrolyte materials, lithium fluorine-containing sulfide electrolyte materials, lithium boron-containing sulfide electrolyte materials, lithium silicon-containing sulfide electrolyte materials, lithium germanium-containing sulfide electrolyte materials, lithium gallium-containing sulfide electrolyte materials, lithium zinc-containing sulfide electrolyte materials, lithium indium-containing sulfide electrolyte materials, lithium aluminum-containing sulfide electrolyte materials, and lithium tin-containing sulfide electrolyte materials. Exemplarily, the aforementioned sulfide electrolyte material may include one or more of lithium phosphorus sulfide, lithium germanium phosphorus sulfide, lithium tin phosphorus sulfide, lithium phosphorus sulfide chloride, lithium phosphorus sulfide bromide, and lithium silicon phosphorus sulfide chloride. In some embodiments, the oxide electrolyte material includes one or more of the following: lithium zirconium-containing oxide electrolyte material, lithium titanium-containing oxide electrolyte material, lithium iron-containing oxide electrolyte material, lithium aluminum-containing oxide electrolyte material, lithium germanium-containing oxide electrolyte material, lithium gallium-containing oxide electrolyte material, lithium lanthanum-containing oxide electrolyte material, lithium silicon-containing oxide electrolyte material, lithium phosphorus-containing oxide electrolyte material, and lithium nitrogen-containing oxide electrolyte material. Exemplarily, the oxide electrolyte material is one or more of the following: lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), lithium lanthanum zirconium tantalum oxide (LLZTO), lithium aluminum germanium phosphate (LAGP), and lithium aluminum titanium phosphate (LATP). In some embodiments, the polymer electrolyte material includes one or more of the following: all-solid-state polymer electrolyte, gel polymer electrolyte, and porous polymer electrolyte. Using the above electrolyte materials can improve the conductivity of the solid electrolyte film, thereby benefiting the initial coulombic efficiency and cycle performance of the secondary battery.

[0086] In some embodiments, the electrolyte material constitutes 88.9% to 99.9% of the solid electrolyte membrane layer by mass, optionally 95% to 99.5%. This results in good lithium-ion conductivity of the electrolyte layer. Exemplarily, the mass percentage of the electrolyte material in the solid electrolyte membrane layer is 88.9%, 90.0%, 92.0%, 95.0%, 96.0%, 97.0%, 98.0%, 99.0%, 99.5%, 99.9%, or a value within a range of any two of these values.

[0087] In some embodiments, the solid electrolyte layer further includes a dispersant; the dispersant includes one or more of polyvinyl alcohol, polyacrylamide, and polyvinylpyrrolidone; optionally, the dispersant includes polyvinyl alcohol. Using the above-mentioned dispersant is beneficial for improving the dispersibility of each component in the electrolyte slurry, and further beneficial for improving the stability of the solid electrolyte membrane layer.

[0088] In some embodiments, the dispersant comprises 0.05% to 2% by mass in the solid electrolyte membrane layer; optionally, it comprises 0.1% to 1%. This is beneficial for the uniform dispersion of the solid electrolyte material. Exemplarily, the dispersant comprises 0.05%, 0.1%, 0.2%, 0.5%, 1.0%, 1.5%, 2.0% by mass in the solid electrolyte membrane layer, or a value within a range of any two of these values.

[0089] In this disclosure, the first binder and the second binder in the secondary battery can be reversed in the following manner: The secondary battery is fully discharged, and the positive and negative electrode plates are disassembled. The solid electrolyte layer adhering to the positive and negative electrode plates is scraped off, and 50g of the scraped solid electrolyte layer is placed in a round-bottom flask. 100mL of toluene is added to the round-bottom flask to dissolve the binder. Then, substances insoluble in toluene (such as electrolyte materials) are filtered out. The filtrate containing the first binder and the second binder is rotary evaporated and concentrated to 10mL. Next, the concentrated filtrate is poured into 100mL of ethanol, so that the mixed powder of the first binder and the second binder precipitates out and is vacuum dried. Finally, the mixed powder is subjected to nuclear magnetic resonance (NMR) testing. The presence of the first binder (polydiolefin binder) is verified by observing the double bond characteristics in the spectrum, and the presence of the second binder (cellulose binder) is verified by observing the glucose ring in the spectrum.

[0090] In this disclosure, the total mass ratio of the first binder and the second binder can be quantitatively tested in the following way. Specifically, the secondary battery is disassembled according to the above method, and the solid electrolyte layer is scraped off. The total weight of the solid electrolyte layer is recorded as W1. Then, the scraped solid electrolyte layer is placed in a round-bottom flask, and 100 mL of toluene is added to the round-bottom flask to fully dissolve the solid electrolyte layer. Then, the electrolyte material that is insoluble in toluene is filtered out, dried, and weighed to obtain the weight of the electrolyte material W2. The total weight of the first binder and the second binder is W1-W2, and the total mass ratio of the first binder and the second binder in the solid electrolyte layer is (W1-W2) / W1*100%.

[0091] In this disclosure, the mass ratio of the first binder and the second binder can be quantitatively determined by nuclear magnetic resonance (NMR) testing. Specifically, the secondary battery is disassembled according to the above method, and a mixed powder of the first binder and the second binder is obtained by the same processing. The content of the first binder and the second binder is determined by measuring the integral area or height of the double bond characteristic peak and the glucose ring specific peak in the NMR spectrum, thereby obtaining the mass ratio of the first binder and the second binder.

[0092] In this disclosure, number-average molecular weight refers to the sum of the products of the mole fractions of molecules with different molecular weights in the polymer and their corresponding molecular weights. It can be tested using methods known in the art, such as gel permeation chromatography (GPC). An exemplary test method is as follows: The first adhesive is dissolved in tetrahydrofuran to prepare a fully dissolved 5 mg / mL solution; then, after filtering through a 0.22 μm to 0.45 μm filter membrane, the solution is placed in a 2 mL chromatographic vial; the vial is placed on an autosampler, and after the GPC baseline stabilizes, the sample is automatically injected for testing. After the test is completed, the number-average molecular weight of the polymer is calculated using a standard curve.

[0093] The term "secondary battery" used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.

[0094] Typically, a single rechargeable battery cell consists of a positive electrode, a negative electrode, and a solid electrolyte layer. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The solid electrolyte layer, positioned between the positive and negative electrodes, acts as a conductor for ions, primarily preventing short circuits between the electrodes while allowing ions to pass through.

[0095] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer comprising a positive active material located on at least one side surface of the positive current collector; the positive active material includes one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium-containing transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds; examples of lithium phosphates include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds.

[0096] In some embodiments, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0097] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0098] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0099] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer comprising a negative electrode active material located on at least one side surface of the negative current collector; the negative electrode active material includes one or more of graphite, soft carbon, hard carbon, and silicon carbon.

[0101] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0102] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0103] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this disclosure is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0104] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0105] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0107] In some implementations, the secondary battery includes a solid-state battery.

[0108] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0109] In some embodiments, the outer packaging of the battery cell can be a rigid 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 flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0110] This disclosure 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 1 shows a square battery cell 5 as an example.

[0111] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a top cover assembly 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 top cover assembly 53 can cover the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator 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 the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0112] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0113] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, 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.

[0114] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0115] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0116] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 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.

[0117] Electrical appliances

[0118] A second aspect of this disclosure provides an electrical device, which includes a secondary battery provided in the first aspect of this disclosure, or a secondary battery prepared according to the preparation method of the second aspect of this disclosure. The secondary battery can be used as a power source for the electrical device or as an 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.

[0119] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0120] Figure 6 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 secondary battery for this device, a battery pack or battery module can be used.

[0121] 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.

[0122] solid electrolyte layer

[0123] A third aspect of this disclosure provides a solid electrolyte layer, including an electrolyte material, a first binder, and a second binder; the first binder includes a polydiolefin binder, and the second binder includes a cellulose binder.

[0124] In this disclosure, the solid electrolyte layer comprises a polydiolefin binder and a cellulose binder. The polydiolefin binder has non-polar segments that interact weakly with the electrolyte material and are stably dispersed in a non-polar solvent. This prevents the electrolyte material from agglomerating or settling, improving the uniformity of electrolyte material distribution in the solid electrolyte layer. Consequently, the lithium-ion transport pathway is uniform, resulting in higher lithium-ion transport efficiency and thus improving the initial coulombic efficiency of the secondary battery. Furthermore, the more uniform distribution of electrolyte material in the solid electrolyte layer reduces lithium plating in the secondary battery, improving its cycle performance. In addition, the polar groups of the cellulose binder interact strongly with the electrolyte material, binding well to its surface and enhancing the stability of the solid electrolyte layer, further improving the cycle performance of the secondary battery.

[0125] In some embodiments, the total mass percentage of the first binder and the second binder in the solid electrolyte layer is 0.1% to 9.1%, optionally 0.1% to 1.5%. This is beneficial for improving the ionic conductivity of the solid electrolyte layer, thereby improving the lithium-ion transport rate in the secondary battery, and consequently improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0126] In some embodiments, the mass ratio of the first binder to the second binder is 1:5 to 10:1, optionally 2:1 to 5:1. This improves both the uniformity of electrolyte material distribution in the solid electrolyte layer and the stability of the solid electrolyte layer, thus enhancing the initial coulombic efficiency and cycle performance of the secondary battery.

[0127] In some embodiments, the first adhesive comprises structural units derived from the monomer shown in Formula 1 and structural units derived from the monomer shown in Formula 2:

[0128] Among them, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, and R15 are each independently one of hydrogen, C1 to C20 alkyl, or C6 to C20 aryl.

[0129] In some embodiments, the first binder includes one or more of poly(2,3-dimethyl-1,3-butadiene), polybutadiene, polyisoprene, polyhexadiene, natural rubber, styrene-butadiene rubber, hydrogenated polybutadiene, hydrogenated polyisoprene, and hydrogenated natural rubber; optionally, the first binder includes poly(2,3-dimethyl-1,3-butadiene). The aforementioned first binder has non-polar segments and flexibility, and these non-polar segments can interact with the electrolyte material with weak forces. This prevents the electrolyte material from agglomerating or settling. Therefore, using the aforementioned first binder is beneficial for improving the uniformity of electrolyte material distribution in the solid electrolyte layer, thereby improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0130] In some embodiments, the number-average molecular weight of the first binder is between 50,000 and 5,000,000, optionally between 500,000 and 2,000,000. A number-average molecular weight within this range is beneficial for improving the uniformity of electrolyte material distribution in the solid electrolyte layer.

[0131] In some embodiments, the structural formula of the cellulose binder is shown in Formula 3:

[0132] Wherein, R1, R2, and R3 are each independently an alkyl group from C1 to C20, an aryl group from C6 to C20, a hydroxyethyl group, or a cyanoethyl group; n is greater than or equal to 50.

[0133] In some embodiments, the second binder includes one or more of methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cyanoethylcellulose, methylhydroxyethylcellulose, and ethylhydroxyethylcellulose; optionally, the second binder includes ethylcellulose. The above-mentioned second binder has good solubility and stable viscosity and adhesion. By using the above-mentioned second binder, it is beneficial to improve the stability of the solid electrolyte membrane layer, thereby improving the cycle performance of the secondary battery.

[0134] In some embodiments, the number-average molecular weight of the second binder is 30,000 to 3,000,000, optionally 500,000 to 2,000,000. A number-average molecular weight within this range is beneficial for the bonding between electrolyte materials and for the bonding between the solid electrolyte layer and the negative and positive electrode sheets.

[0135] In some embodiments, the electrolyte material includes one or more of sulfide electrolyte materials, oxide electrolyte materials, and polymer electrolyte materials. Using the above-mentioned electrolyte materials can improve the conductivity of the solid electrolyte film, thereby benefiting the initial coulombic efficiency and cycle performance of the secondary battery.

[0136] In some embodiments, the electrolyte material accounts for 88.9% to 99.9% of the mass of the solid electrolyte membrane layer, optionally 95% to 99.5%. Therefore, the electrolyte layer exhibits good lithium-ion conductivity.

[0137] In some embodiments, the solid electrolyte layer further includes a dispersant; the dispersant includes one or more of polyvinyl alcohol, polyacrylamide, and polyvinylpyrrolidone; optionally, the dispersant includes polyvinyl alcohol. Using the above-mentioned dispersant is beneficial for improving the dispersibility of each component in the electrolyte slurry, and further beneficial for improving the stability of the solid electrolyte membrane layer.

[0138] In some embodiments, the dispersant accounts for 0.05% to 2% by mass in the solid electrolyte membrane layer; alternatively, it accounts for 0.1% to 1%. This is beneficial for the uniform dispersion of the solid electrolyte material.

[0139] Preparation method of solid electrolyte layer

[0140] The fourth aspect of this disclosure provides a method for preparing a solid electrolyte layer, comprising the following steps: a preparation step, comprising dissolving an electrolyte material, a first binder, and a second binder in a non-polar solvent to form a solid electrolyte slurry; wherein the first binder includes a polydiolefin binder, and the second binder includes a cellulose binder; and a coating step, comprising coating the solid electrolyte slurry to form a solid electrolyte layer.

[0141] In this disclosure, a polydiolefin binder and a non-polar solvent are used in combination when preparing the solid electrolyte slurry. Because the polydiolefin binder can be dispersed uniformly in the non-polar solvent for a long time, and the non-polar segments in the polydiolefin binder can interact with the electrolyte material with weak forces to stably disperse in the non-polar solvent, the electrolyte material does not agglomerate or settle. Therefore, continuous stirring of the solid electrolyte slurry is not required before coating, reducing energy consumption and preventing the introduction of air bubbles, which is beneficial to the processing performance, initial coulombic efficiency, and cycle performance of the secondary battery. In addition, a cellulose binder is also used in the preparation of the solid electrolyte slurry. Cellulose binders have polar groups that interact strongly with the electrolyte material, allowing them to bind well to the surface of the electrolyte material, thereby improving the stability of the solid electrolyte layer. The solid electrolyte layer prepared by this disclosure has high film stability and uniform electrolyte material distribution, which is beneficial to the initial coulombic efficiency and cycle performance of the secondary battery.

[0142] In some embodiments, the solid electrolyte slurry has a solid content of 30% to 80%, optionally 45% to 70%. A solid content within this range is advantageous for forming a uniformly coated solid electrolyte layer. Exemplarily, the solid electrolyte slurry has a solid content of 30%, 40%, 45%, 50%, 60%, 70%, 80%, or a value within a range of any two of these values.

[0143] In some embodiments, the total content of the first binder and the second binder in the solid electrolyte slurry, based on the total weight of solids in the solid electrolyte slurry, is from 0.1% to 9.1%, optionally from 0.1% to 1.5%. This is beneficial for improving the ionic conductivity of the solid electrolyte layer, thereby improving the lithium-ion transport rate in the secondary battery, and consequently improving the initial coulombic efficiency and cycle performance of the secondary battery. Exemplarily, the total content of the first binder and the second binder in the solid electrolyte slurry, based on the total weight of solids in the solid electrolyte slurry, is 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 8.5%, 9.1%, or a value within a range of any two of these values.

[0144] In some embodiments, the mass ratio of the first binder to the second binder in the solid electrolyte slurry, based on the total weight of solids in the solid electrolyte slurry, is 1:5 to 10:1, optionally 2:1 to 5:1. This improves both the uniformity of electrolyte material distribution in the solid electrolyte layer and the stability of the solid electrolyte layer, thus enhancing the initial coulombic efficiency and cycle performance of the secondary battery. Exemplarily, the mass ratio of the first binder to the second binder is 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or a value within a range of any two of these values.

[0145] In some embodiments, the first adhesive comprises structural units derived from the monomer shown in Formula 1 and structural units derived from the monomer shown in Formula 2:

[0146] Among them, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, and R15 are each independently one of hydrogen, C1 to C20 alkyl, or C6 to C20 aryl.

[0147] In some embodiments, the first binder includes one or more of poly(2,3-dimethyl-1,3-butadiene), polybutadiene, polyisoprene, polyhexadiene, natural rubber, styrene-butadiene rubber, hydrogenated polybutadiene, hydrogenated polyisoprene, and hydrogenated natural rubber; optionally, the first binder includes poly(2,3-dimethyl-1,3-butadiene). The aforementioned first binder has non-polar segments and flexibility, and these non-polar segments can interact with the electrolyte material with weak forces. This prevents the electrolyte material from agglomerating or settling. Therefore, using the aforementioned first binder is beneficial for improving the uniformity of electrolyte material distribution in the solid electrolyte layer, thereby improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0148] In some embodiments, the number-average molecular weight of the first binder is between 50,000 and 5,000,000, optionally between 500,000 and 2,000,000. A number-average molecular weight within this range is beneficial for improving the uniformity of electrolyte material distribution in the solid electrolyte layer.

[0149] In some embodiments, the structural formula of the cellulose binder is shown in Formula 3:

[0150] R1, R2, and R3 are each independently one of alkyl (C1 to C20), aryl (C6 to C20), hydroxyethyl, and cyanoethyl; n is greater than or equal to 50.

[0151] In some embodiments, the second binder includes one or more of methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cyanoethylcellulose, methylhydroxyethylcellulose, and ethylhydroxyethylcellulose; optionally, the second binder includes ethylcellulose. The above-mentioned second binder has good solubility and stable viscosity and adhesion. By using the above-mentioned second binder, it is beneficial to improve the stability of the solid electrolyte membrane layer, thereby improving the cycle performance of the secondary battery.

[0152] In some embodiments, the number average molecular weight of the second binder is 30,000 to 3,000,000, optionally 500,000 to 2,000,000. A number average molecular weight within this range is beneficial for the adhesion between electrolyte materials and for the adhesion between the solid electrolyte layer and the negative and positive electrode sheets.

[0153] In some embodiments, the nonpolar solvent includes one or more hydrocarbons that are liquid at room temperature, such as toluene, xylene, trimethylbenzene, heptane, octane, nonane, decane, undecane, dodecane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cyclododecane, and decahydronaphthalene. The first binder in the aforementioned electrolyte slurry can be dispersed uniformly in the nonpolar solvent for a long time, improving the dispersion uniformity of the electrolyte material in the electrolyte slurry, thereby improving the uniformity of the solid electrolyte layer, and consequently benefiting the initial coulombic efficiency and cycle performance of the secondary battery.

[0154] In some embodiments, the nonpolar solvent includes hydrocarbons that are liquid at 25°C.

[0155] Example

[0156] The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0157] Example 1

[0158] Preparation of secondary batteries

[0159] Preparation of the positive electrode: In an anhydrous and oxygen-free environment, nickel-cobalt-manganese ternary material (LiNi) was mixed in a weight ratio of 7:2:1. 0.83 Co 0.12 Mn 0.05 O2), sulfide solid electrolyte, and conductive carbon black are mixed and then added to toluene solvent. After mixing, the mixture is coated on both sides of aluminum foil. After cold pressing and cutting, the positive electrode sheet is obtained and dried for later use.

[0160] Preparation of solid electrolyte: a) Preparation of solid electrolyte slurry: Dissolve 1.97g of silver-germanium sulfide electrolyte material, 0.02g of second binder ethyl cellulose, and 0.01g of first binder poly(2,3-dimethyl-1,3-butadiene) in 2.03g of nonpolar solvent toluene, and disperse at 1000rpm for 30min to obtain a solid electrolyte slurry with a solid content of 50%; b) Coat the solid electrolyte slurry from step a uniformly onto the dried positive electrode without settling, and dry again to obtain a solid electrolyte layer. In step a, based on the total solid mass of the solid electrolyte slurry, the total content of the first binder poly(2,3-dimethyl-1,3-butadiene) and the second binder ethyl cellulose is 1.5%, the mass ratio of the first binder poly(2,3-dimethyl-1,3-butadiene) to the second binder ethyl cellulose is 1:2, the mass proportion of the silver-sulfur germanium ore electrolyte material is 98.5%, the number average molecular weight of the first binder poly(2,3-dimethyl-1,3-butadiene) is 1 million, and the number average molecular weight of the second binder ethyl cellulose is 500,000. In step b, the thickness of the obtained solid electrolyte layer is 1.121 mm.

[0161] Preparation of negative electrode sheet: Silicon carbon material, conductive carbon black, binder carboxymethyl cellulose (CMC) and solvent water are uniformly mixed in a weight ratio of 95:2:3:100, coated on both sides of copper foil, and then cold-pressed and cut to obtain negative electrode sheet.

[0162] Preparation of secondary batteries: The batteries are arranged in the order of "positive electrode - electrolyte membrane - negative electrode" and then subjected to a pressure of 2MPa to form a mold battery.

[0163] Examples 2-5

[0164] Solid electrolyte slurry and solid electrolyte layer were prepared in a manner similar to that in Example 1 and assembled into a secondary battery. The only difference was that the contents of the second binder and the first binder were adjusted according to Table 1 below when preparing the solid electrolyte slurry.

[0165] Comparative Example 1

[0166] Solid electrolyte slurry and solid electrolyte layer were prepared in a manner similar to that in Example 1 and assembled into a secondary battery. The only difference was that when preparing the solid electrolyte slurry, only the second binder was added and the first binder was not added.

[0167] Comparative Example 2

[0168] Solid electrolyte slurry and solid electrolyte layer were prepared in a manner similar to that in Example 1 and assembled into a secondary battery. The only difference was that when preparing the solid electrolyte slurry, only the first binder was added and the second binder was not added.

[0169] Comparative Examples 3-4

[0170] Solid electrolyte slurry and solid electrolyte layer were prepared in a manner similar to that in Example 1 and assembled into a secondary battery, the only difference being that the types of the first binder and the second binder were adjusted according to Table 1 below when preparing the solid electrolyte slurry.

[0171] Solid electrolyte slurry performance testing

[0172] 1) Settlement effect test:

[0173] The solid electrolyte slurry prepared in step a of the above embodiments was allowed to stand for 12 hours under sealed conditions in a glove box. The sedimentation of the solid electrolyte slurry was visually observed and recorded, and the results are shown in Table 1.

[0174] Figure 7 shows a schematic diagram of the structure of the solid electrolyte slurry in Example 1 after standing for 12 hours, and Figure 8 shows a schematic diagram of the structure of the solid electrolyte slurry in Comparative Example 1 after standing for 12 hours. It can be seen that the solid electrolyte slurry in Example 1 did not settle after standing for 12 hours, while the solid electrolyte slurry in Comparative Example 1 settled after standing for 12 hours.

[0175] 2) Ion conductivity test

[0176] The solid electrolyte slurry prepared in the above embodiments was coated onto aluminum foil, dried, and then the AC impedance spectrum of the solid electrolyte layer was tested. The bulk impedance value of the solid electrolyte layer was read from the measured AC impedance spectrum, and then the ionic conductivity of the solid electrolyte layer was calculated according to the following formula (1):

[0177]

[0178] In the formula, σ is the ionic conductivity, L is the thickness of the solid electrolyte layer, S is the area of ​​the solid electrolyte layer, and R is the measured bulk impedance value.

[0179] The solid electrolyte slurry prepared in Example 1 had a bulk impedance of 52.5 Ω as measured by the above method. The ionic conductivity of the solid electrolyte layer was calculated to be 2.72 mS / cm using the above formula (1), where the thickness L of the solid electrolyte layer was 1.121 mm and the area S of the solid electrolyte layer was 0.785 cm². 2 .

[0180] Performance testing of secondary batteries

[0181] 1) First Coulomb efficiency test

[0182] The following test steps were performed on the secondary battery in Example 1 at 25°C:

[0183] ① Let stand for 5 minutes;

[0184] ② Charge at a constant current of 0.1C to 3.68V, then charge at a constant voltage of 3.68V to a current of 0.05C, and record the charging capacity C1 of the first cycle;

[0185] ③ Let stand for 5 minutes;

[0186] ④ Discharge at a constant current of 0.33C to 1.98V, and record the discharge capacity D1 of the first cycle;

[0187] First Coulomb efficiency (%) = first discharge capacity D1 / first charge capacity C1 * 100%.

[0188] 2) Cyclic performance test

[0189] The following test steps were performed on the secondary battery in Example 1 at 25°C:

[0190] ① Let stand for 5 minutes;

[0191] ② Charge at a constant current of 0.1C to 3.68V, then charge at a constant voltage of 3.68V to a current of 0.05C;

[0192] ③ Let stand for 5 minutes;

[0193] ④ Discharge at a constant current of 0.33C to 1.98V, and record the discharge capacity D1 of the first cycle;

[0194] ⑤ Repeat steps ① to ④ above 1000 times, and record the discharge capacity Dn on the 1000th cycle;

[0195] Capacity retention rate after 1000 cycles (%) = Discharge capacity Dn of the 1000th cycle / Discharge capacity D1 of the first cycle * 100%. The test results are shown in Table 2.

[0196] Table 1 below shows the performance parameters and sedimentation effect test results of the solid electrolyte slurries prepared in Examples 1-5 and Comparative Examples 1-4. Table 2 below shows the ionic conductivity of the solid electrolyte slurries prepared in Examples 1-5 and Comparative Examples 1-4, as well as the initial coulombic efficiency and cycle performance of the secondary batteries.

[0197] Table 1

[0198] In Table 1, " / " indicates that the symbol does not exist.

[0199] Table 2

[0200] Based on the results in Tables 1 and 2 above, it can be seen that compared to Comparative Example 1 (which only used cellulose-based binders), Examples 1-5, by including both polydiolefin and cellulose-based binders in the solid electrolyte slurry, prevented sedimentation after 12 hours of standing, significantly improving the processing performance of the secondary battery. Comparative Example 2, containing only polydiolefin binders, improved the processing performance of the secondary battery, but the solid electrolyte layer had low conductivity, resulting in poor initial coulombic efficiency and cycle performance. Comparative Example 3, containing polydiolefin binders but not cellulose-based binders, improved the processing performance of the secondary battery, but the solid electrolyte layer had low conductivity, resulting in poor initial coulombic efficiency and cycle performance. Comparative Example 4, containing cellulose-based binders but not polydiolefin binders, caused sedimentation of the solid electrolyte slurry after 12 hours of standing, resulting in poor processing performance of the secondary battery.

[0201] In addition, when the total mass percentage of polydiolefin binders and cellulose binders in the solid electrolyte layer is between 0.1% and 9.1%, the processing performance, initial coulombic efficiency, and cycle performance of the secondary battery can be significantly improved.

[0202] Examples 6-8

[0203] Solid electrolyte slurry and solid electrolyte layer were prepared in a manner similar to that in Example 1 and assembled into a secondary battery. The only difference was that the mass ratio of the first binder to the second binder was adjusted according to Table 3 below when preparing the solid electrolyte slurry.

[0204] Table 3 below shows the performance parameters of the solid electrolyte slurry prepared in Examples 6-8, and Table 4 below shows the performance parameters of the solid electrolyte layer in Examples 6-8 and the test results of the secondary battery.

[0205] Table 3

[0206] Table 4

[0207] According to the results in Tables 3 and 4 above, controlling the mass ratio of cellulose binder to polydiolefin binder in the solid electrolyte layer to be 1:5 to 10:1 significantly improves the processing performance, initial coulombic efficiency, and cycle performance of the secondary battery.

[0208] Examples 9-16

[0209] Solid electrolyte slurry and solid electrolyte layer were prepared using a method similar to that in Example 1, and assembled into a secondary battery. The only difference was that the types of the first and second binders were adjusted according to Table 5 below when preparing the solid electrolyte slurry. Specifically, the binder content in the solid electrolyte slurry was 1.5% based on the total solid weight, and the mass ratio of the second binder to the first binder was 2:1.

[0210] Table 5 below shows the performance parameters of the solid electrolyte slurry prepared in Examples 9-16, and Table 6 below shows the performance parameters of the solid electrolyte layer prepared in Examples 9-16 and the test results of the secondary battery.

[0211] Table 5

[0212] Table 6

[0213] According to the results in Tables 5 and 6 above, when any one of the following polydiolefin binders is selected: polybutadiene, polyisoprene, polyhexadiene, natural rubber, styrene-butadiene rubber, hydrogenated polybutadiene, hydrogenated polyisoprene, or hydrogenated natural rubber, and when any one of the following cellulose binders is selected: methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cyanoethylcellulose, methylhydroxyethylcellulose, or ethylhydroxyethylcellulose, the processing performance, initial coulombic efficiency, and cycle performance of the secondary battery can be improved.

[0214] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. 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, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode; The solid electrolysis layer includes an electrolyte material, a first binder, and a second binder; The first adhesive includes a polydiolefin adhesive, and the second adhesive includes a cellulose adhesive.

2. The secondary battery according to claim 1, wherein, The total mass percentage of the first binder and the second binder in the solid electrolyte layer is between 0.1% and 9.1%.

3. The secondary battery according to claim 1 or 2, wherein, The total mass percentage of the first and second binders in the solid electrolyte layer is 0.1% to 1.5%.

4. The secondary battery according to any one of claims 1 to 3, wherein, The mass ratio of the first adhesive to the second adhesive is 1:5 to 10:

1.

5. The secondary battery according to any one of claims 1 to 4, wherein, The mass ratio of the first adhesive to the second adhesive is 2:1 to 5:

1.

6. The secondary battery according to any one of claims 1 to 5, wherein, The first adhesive comprises structural units derived from the monomer shown in Formula 1 and structural units derived from the monomer shown in Formula 2: Among them, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, and R15 are each independently one of hydrogen, C1 to C20 alkyl, or C6 to C20 aryl.

7. The secondary battery according to any one of claims 1 to 6, wherein, The first adhesive includes one or more of poly(2,3-dimethyl-1,3-butadiene), polybutadiene, polyisoprene, polyhexadiene, natural rubber, styrene-butadiene rubber, hydrogenated polybutadiene, hydrogenated polyisoprene, and hydrogenated natural rubber.

8. The secondary battery according to any one of claims 1 to 7, wherein, The first adhesive comprises poly(2,3-dimethyl-1,3-butadiene).

9. The secondary battery according to any one of claims 1 to 8, wherein, The number average molecular weight of the first adhesive is between 50,000 and 5 million.

10. The secondary battery according to any one of claims 1 to 9, wherein, The second adhesive comprises the compound shown in Formula 3: R1, R2, and R3 are each independently one of C1-C20 alkyl, C6-C20 aryl, hydroxyethyl, and cyanoethyl; n is greater than or equal to 50.

11. The secondary battery according to any one of claims 1 to 10, wherein, The second binder includes one or more of methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cyanoethylcellulose, methylhydroxyethylcellulose, and ethylhydroxyethylcellulose.

12. The secondary battery according to any one of claims 1 to 11, wherein, The second binder includes ethyl cellulose.

13. The secondary battery according to any one of claims 1 to 12, wherein, The number average molecular weight of the second adhesive is between 30,000 and 3 million.

14. The secondary battery according to any one of claims 1 to 13, wherein, The electrolyte material includes one or more of sulfide electrolyte materials, oxide electrolyte materials, and polymer electrolyte materials.

15. The secondary battery according to any one of claims 1 to 14, wherein, The electrolyte material accounts for 88.9% to 99.9% of the mass of the solid electrolyte layer.

16. The secondary battery according to any one of claims 1 to 15, wherein, The solid electrolyte layer further includes a dispersant; the dispersant accounts for 0.05% to 2% of the mass of the solid electrolyte layer.

17. The secondary battery according to any one of claims 1 to 16, wherein, The secondary battery includes a solid-state battery.

18. An electrical device comprising a secondary battery as described in any one of claims 1 to 17.

19. A solid electrolyte layer, comprising an electrolyte material, a first binder, and a second binder; The first adhesive includes a polydiolefin adhesive, and the second adhesive includes a cellulose adhesive.

20. The solid electrolyte layer according to claim 19, wherein, The total mass percentage of the first binder and the second binder in the solid electrolyte layer is between 0.1% and 9.1%.

21. The solid electrolyte layer according to claim 19 or 20, wherein, The mass ratio of the first adhesive to the second adhesive is 1:5 to 10:

1.

22. The solid electrolyte layer according to any one of claims 19 to 21, wherein, The first adhesive comprises structural units derived from the monomer shown in Formula 1 and structural units derived from the monomer shown in Formula 2: Among them, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, and R15 are each independently one of hydrogen, C1 to C20 alkyl, or C6 to C20 aryl.

23. The solid electrolyte layer according to any one of claims 19 to 22, wherein, The first adhesive includes one or more of poly(2,3-dimethyl-1,3-butadiene), polybutadiene, polyisoprene, polyhexadiene, natural rubber, styrene-butadiene rubber, hydrogenated polybutadiene, hydrogenated polyisoprene, and hydrogenated natural rubber.

24. The solid electrolyte layer according to any one of claims 19 to 23, wherein, The number average molecular weight of the first adhesive is between 50,000 and 5 million.

25. The solid electrolyte layer according to any one of claims 19 to 24, wherein, The second adhesive comprises the compound shown in Formula 3: R1, R2, and R3 are each independently one of C1-C20 alkyl, C6-C20 aryl, hydroxyethyl, and cyanoethyl; n is greater than or equal to 50.

26. The solid electrolyte layer according to any one of claims 19 to 25, wherein, The second binder includes one or more of methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cyanoethylcellulose, methylhydroxyethylcellulose, and ethylhydroxyethylcellulose.

27. The solid electrolyte layer according to any one of claims 19 to 26, wherein, The number average molecular weight of the second adhesive is between 30,000 and 3 million.

28. The solid electrolyte layer according to any one of claims 19 to 27, wherein, The electrolyte material includes one or more of sulfide electrolyte materials, oxide electrolyte materials, and polymer electrolyte materials.

29. A method for preparing a solid electrolyte layer, comprising the following steps: The preparation step includes dissolving the electrolyte material, the first binder, and the second binder in a non-polar solvent to form a solid electrolyte slurry; wherein the first binder includes a polydiolefin binder, and the second binder includes a cellulose binder; The coating step includes coating the solid electrolyte slurry to form a solid electrolyte layer.

30. The preparation method according to claim 29, wherein, Based on the total weight of solids in the solid electrolyte slurry, the total content of the first binder and the second binder in the solid electrolyte slurry is from 0.1% to 9.1%.

31. The preparation method according to claim 29 or 30, wherein, Based on the total weight of solids in the solid electrolyte slurry, the mass ratio of the first binder to the second binder in the solid electrolyte slurry is 1:5 to 10:

1.

32. The preparation method according to any one of claims 29 to 31, wherein, The first adhesive comprises structural units derived from the monomer shown in Formula 1 and structural units derived from the monomer shown in Formula 2: Among them, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, and R15 are each independently one of hydrogen, C1 to C20 alkyl, or C6 to C20 aryl.

33. The preparation method according to any one of claims 29 to 32, wherein, The first adhesive includes one or more of poly(2,3-dimethyl-1,3-butadiene), polybutadiene, polyisoprene, polyhexadiene, natural rubber, styrene-butadiene rubber, hydrogenated polybutadiene, hydrogenated polyisoprene, and hydrogenated natural rubber.

34. The preparation method according to any one of claims 29 to 33, wherein, The number average molecular weight of the first adhesive is between 50,000 and 5 million.

35. The preparation method according to any one of claims 29 to 34, wherein, The second adhesive comprises the compound shown in Formula 3: R1, R2, and R3 are each independently one of C1-C20 alkyl, C6-C20 aryl, hydroxyethyl, and cyanoethyl; n is greater than or equal to 50.

36. The preparation method according to any one of claims 29 to 35, wherein, The second binder includes one or more of methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cyanoethylcellulose, methylhydroxyethylcellulose, and ethylhydroxyethylcellulose.

37. The preparation method according to any one of claims 29 to 36, wherein, The number average molecular weight of the second adhesive is between 30,000 and 3 million.

38. The preparation method according to any one of claims 29 to 37, wherein, The nonpolar solvent includes one or more of toluene, xylene, trimethylbenzene, heptane, octane, nonane, decane, undecane, dodecane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cyclododecane, and decahydronaphthalene.

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