Composite Binder and Electrochemical Device and Electronic Device Containing the Same

Abstract

This application relates to a composite binder and an electrochemical device and an electronic device comprising the same. The composite binder includes: a polymer binder and a fiber reinforcement, wherein the polymer binder is a solution-type binder, which comprises a homopolymer or a copolymer, and the monomers of the homopolymer or the copolymer include at least one of acrylic acid, alginic acid, acrylonitrile, acrylamide, and vinyl alcohol. By adopting the above composite binder, the structural strength of the negative electrode active material layer can be effectively improved, so that the electrochemical device has good cycle performance and safety performance.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage, and in particular to a composite binder and an electrochemical device and an electronic device comprising the composite binder. Background Art

[0002] With the rapid development of mobile electronic technology, people's frequency of using mobile electronic devices such as mobile phones, tablets, laptops, drones, etc. and experience requirements are getting higher and higher. Therefore, an electrochemical device (for example, a lithium-ion battery) that provides energy for an electronic device needs to exhibit higher energy density, greater rate performance, higher safety, and smaller capacity attenuation after repeated charge and discharge processes.

[0003] The energy density and cycle efficiency of an electrochemical device are closely related to its positive electrode active material and negative electrode active material. In view of this, people have continuously conducted further research and improvement on the negative electrode active material to pursue a negative electrode active material with higher energy density. However, materials with high energy density (for example, silicon-based materials) often have problems that do not match the existing electrode assembly structure, such as too low electrical conductivity, too high thermal expansion rate, insufficient processing performance, and so on. Therefore, in addition to improving and replacing the negative electrode active material with high energy density, it is also necessary to further improve and study its related negative electrode additives (for example, binders and conductive agents). Summary of the Invention

[0004] The present application provides a composite binder and an electrochemical device and an electronic device comprising the composite binder in an attempt to solve at least one problem existing in the related art to at least some extent.

[0005] According to one aspect of the present application, the present application provides a composite binder, which comprises: a polymer binder and a fiber reinforcement, wherein the polymer binder is a solution-type binder, which comprises a homopolymer or a copolymer, and the monomers of the homopolymer or the copolymer include at least one of acrylic acid, alginic acid, acrylonitrile, acrylamide, and vinyl alcohol.

[0006] By adopting the above composite binder, the present application can effectively improve the structural strength of the negative electrode active material layer, so that the electrochemical device has good cycle performance and safety performance.

[0007] According to another aspect of the present application, the present application provides an electrochemical device, which comprises a positive electrode, a separator, and a negative electrode. The negative electrode comprises a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer comprises a silicon-based material, a carbon-based material, and the composite binder in the above embodiments.

[0008] According to another aspect of the present application, the present application provides an electronic device, which includes the above-mentioned electrochemical device.

[0009] Additional aspects and advantages of the embodiments of the present application will be described, shown, or elucidated in part in the subsequent description, or by the implementation of the embodiments of the present application. Brief Description of the Drawings

[0010] The drawings necessary for describing the embodiments of the present application or the prior art will be briefly described hereinafter to facilitate the description of the embodiments of the present application. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings of embodiments can still be obtained based on the structures illustrated in these drawings.

[0011] Figure 1 Schematic diagram of a composite binder according to some embodiments of the present application.

[0012] Figure 2 Tensile strength curve of a composite binder formed by mixing a polymer binder and a fiber reinforcement in different weight ratios.

[0013] Figure 3 Tensile strength curve of a composite binder formed by mixing various polymer binders and different fiber reinforcements in the same ratio. Detailed Description of the Embodiments

[0014] The embodiments of the present application will be described in detail hereinafter. Throughout the specification of the present application, components that are the same or similar and have the same or similar functions are denoted by like reference numerals. The embodiments of the present application described with reference to the drawings are illustrative, diagrammatic, and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as a limitation of the present application.

[0015] As used herein, the terms "substantially", "generally", "essentially" and "about" are used to describe and account for minor variations. When used in connection with an event or circumstance, the term can refer to instances where the event or circumstance occurs precisely as well as instances where the event or circumstance occurs very nearly. For example, when used in connection with a numerical value, the term can refer to a variation range of less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, if the difference between two numerical values is less than or equal to ±10% of the average value of the value (e.g., less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%), then the two numerical values can be considered "substantially" the same.

[0016] In addition, sometimes quantities, ratios, and other numerical values are presented herein in a range format. It should be understood that such range formats are for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly specified as range limitations, but also all individual numerical values or sub-ranges subsumed within that range as if each numerical value and sub-range were explicitly specified.

[0017] In the detailed description and claims, a list of items connected by the terms "at least one of", "at least one in", "at least one kind in", or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0018] Unless otherwise expressly specified, the following terms used herein have the meanings set forth below.

[0019] The term "alginic acid" refers to a linear block polyglycuronic acid, an organic acid polymer formed by homopolymeric α-L-guluronic acid blocks, homopolymeric β-D-mannuronic acid blocks, and alternating blocks of these two uronic acids, linked by 1,4-glycosidic bonds. The term "alginates" refers to derivatives formed by alginic acid and salts, including, but not limited to, at least one of calcium salts, magnesium salts, sodium salts, potassium salts, strontium salts.

[0020] The term "polyethylene polymer" refers to a polymer composed of ethylenic monomers, which can be derivatives formed by ethylene and the functional groups of any substituents, including, but not limited to, vinyl alcohol. For example, polyvinyl alcohol is expected to be a polymer composed of vinyl alcohol monomers.

[0021] The term "polypropylene polymer" refers to a polymer composed of propylene monomers, which can be derivatives formed by propylene and the functional groups of any substituents, including, but not limited to, at least one of acrylic acid, acrylonitrile, and acrylamide. For example, polyacrylic acid is expected to be a polymer composed of acrylic acid monomers. Polyacrylonitrile is expected to be a polymer composed of acrylonitrile monomers. Polyacrylamide is expected to be a polymer composed of acrylamide monomers.

[0022] The terms "carboxymethyl cellulose", "carboxyethyl cellulose", and "carboxypropyl cellulose" respectively refer to celluloses with carboxymethyl, carboxyethyl, and carboxypropyl substituents. The terms "carboxymethyl cellulose salts", "carboxyethyl cellulose salts", and "carboxypropyl cellulose salts" respectively refer to derivatives formed by carboxymethyl cellulose, carboxyethyl cellulose, and carboxypropyl cellulose and salts, and the salts include, but not limited to, at least one of calcium salts, magnesium salts, sodium salts, potassium salts, and strontium salts.

[0023] The term "fiber" refers to solid fibers with low solubility.

[0024] In the field of electrochemical devices, in order to pursue the best energy density, attempts have been made to replace graphite in traditional anode active materials with anode active materials with high energy density. However, when applying such high-energy-density anode active materials, further process treatment is required due to different material properties. For example, silicon-based materials are the mainstream anode active materials for the development of future electrochemical devices with high volumetric energy density (such as lithium-ion batteries) due to their theoretical specific capacity of up to 4200 mAh / g. Such high-energy-density anode active materials have a huge volume change effect during the lithium insertion / extraction process (for example, greater than about 300%). Severe swelling of the anode will cause deformation or even separation of the interface between the anode and the separator, thereby reducing the cycling performance of the lithium-ion battery. Therefore, excessive volume expansion during the charge / discharge cycle will not only cause deformation of the electrode assembly and reduce the cycling performance, but also easily lead to damage to the structure of the lithium-ion battery, seriously affecting the safety of the lithium-ion battery.

[0025] From the perspective of improving the swelling of the negative electrode, this application studies how to enhance the bonding ability (cohesion) between the particles of the negative electrode active material in the negative electrode active material layer to inhibit the cyclic swelling of the negative electrode during charging. This application provides a composite binder with high bonding and high toughness properties. By adding it to the negative electrode active material, it bonds and coats the surface of the particles of the negative electrode active material, forming a bridging between the particles, thereby effectively enhancing the cohesion of the negative electrode. Compared with the existing water-soluble binders, the composite binder of this application includes a polymer binder and a fiber reinforcement, making the composite binder have high strength, toughness and heat resistance. Moreover, due to the high degree of orientation and crystallinity of the fiber reinforcement (for example, between 50% and 70%), the tensile strength of the composite binder can be effectively improved. In addition, the hydroxyl groups of the fiber reinforcement can chemically bond or form hydrogen bonds with the carboxyl and hydroxyl groups of the polymer binder, thereby forming a good composite structure. This composite structure can give full play to the high tensile strength advantage of the fiber reinforcement, can support the negative electrode active material during the charging process, reduce the degree of deformation and swelling rate of the negative electrode during the charge-discharge cycle, and ensure the cycle performance and rate performance of the electrochemical device.

[0026] According to one aspect of this application, an embodiment of this application provides a composite binder, which includes: a polymer binder and a fiber reinforcement. The polymer binder is a solution-type binder, which includes a homopolymer or a copolymer, and the monomers of the homopolymer or the copolymer include at least one of acrylic acid, alginic acid, acrylonitrile, acrylamide, and vinyl alcohol.

[0027] In some embodiments, the fiber reinforcement includes at least one of cellulose fiber, carboxymethyl cellulose fiber and its derivatives, hydroxyethyl cellulose fiber and its derivatives, hydroxypropyl cellulose fiber and its derivatives, and polyvinyl alcohol fiber. In some embodiments, the fiber reinforcement is composed of polyvinyl alcohol fiber.

[0028] In some embodiments, the weight average molecular weight of the polymer binder is 100 kDa to 10,000 kDa. In some other embodiments, the weight average molecular weight of the polymer binder is approximately, for example, about 100 kDa, about 200 kDa, about 500 kDa, about 1,000 kDa, about 2,000 kDa, about 5,000 kDa, about 8,000 kDa, about 10,000 kDa, or a range composed of any two of these values.

[0029] In some embodiments, the fiber reinforcement is a strip-shaped fiber.

[0030] In some embodiments, the length of the fiber reinforcement is from 5 μm to 100 μm. In other embodiments, the length of the fiber reinforcement is approximately, for example, about 5 μm, about 10 μm, about 20 μm, about 30 μm, about 40 μm, about 50 μm, about 75 μm, about 100 μm, or any range formed by any two of these values.

[0031] In some embodiments, the diameter of the fiber reinforcement is from 0.001 μm to 1.0 μm. In other embodiments, the diameter of the fiber reinforcement is approximately, for example, about 0.001 μm, about 0.01 μm, about 0.05 μm, about 0.1 μm, about 0.2 μm, about 0.3 μm, about 0.4 μm, about 0.5 μm, about 1.0 μm, or any range formed by any two of these values.

[0032] The terms "length" and "diameter" are common parameters used to simplify the description of the morphology of the fiber reinforcement; the length is the fiber length measured from one end to the other end of the fiber reinforcement by a scanning electron microscope. The diameter is the fiber diameter of the cross-section of the fiber reinforcement.

[0033] In some embodiments, the aspect ratio of the length to the diameter of the fiber reinforcement is from 100 to 10,000. In other embodiments, the aspect ratio of the fiber reinforcement is approximately, for example, about 100, about 200, about 500, about 1000, about 2500, about 5000, about 10,000, or any range formed by any two of these values.

[0034] Figure 1 It is a schematic diagram of a composite binder according to some embodiments of the present application.

[0035] As Figure 1 shown, the fiber reinforcement 20 remains in the form of long solid fibers in the polymer binder 10.

[0036] In some embodiments, the solid content of the composite binder is from 1% to 60%. In other embodiments, the solid content of the composite binder is approximately, for example, about 1%, about 2%, about 5%, about 10%, about 20%, about 50%, about 60%, or any range formed by any two of these values.

[0037] As used herein, the term "solid content" refers to the weight percentage of all solids in a solution. For example, the solid content of the composite binder includes the solid contents of two substances, namely, the "polymer binder" and the "fiber reinforcement". The method for testing the solid content of the composite binder provided by some embodiments of the present application is to dry the composite binder at 130 °C to 200 °C and calculate the weight ratio of the remaining solids after drying.

[0038] In some embodiments, the particle size Dv50 of the composite binder is from 1 μm to 100 μm. In other embodiments, the particle size Dv50 of the composite binder is approximately, for example, about 1 μm, about 5 μm, about 10 μm, about 20 μm, about 50 μm, about 100 μm, or a range formed by any two of these values.

[0039] As used herein, the term "particle size" represents the characteristic particle property Dv50 obtained by laser particle size testing of a sample, where Dv50 represents the particle size at which, starting from the small particle size side, the cumulative volume of the material reaches 50% in the particle size distribution on a volume basis. The particle size testing method provided by the embodiments of the present application is to analyze the particle size of the particles of the sample using a Mastersizer 2000 laser particle size distribution tester: the sample is dispersed in 100 mL of a dispersant (deionized water) to make the obscuration reach 8 - 12%. Subsequently, the sample is ultrasonically treated for 5 minutes at an ultrasonic intensity of 40 KHz and 180 w. After the ultrasonic treatment, the sample is subjected to laser particle size distribution analysis to obtain particle size distribution data.

[0040] According to some embodiments of the present application, the composite binder can effectively improve the tensile strength by mixing a certain proportion of a polymer binder (for example, polyacrylic acid, PAA) and a fiber reinforcement (for example, polyvinyl alcohol fiber), thereby providing good cohesion between the particles of the negative electrode active material. As Figure 2 and 3 shown, the tensile strength of the composite binder formed by using polyacrylic acid as the polymer binder and polyvinyl alcohol fiber as the fiber reinforcement can reach 3100 MPa. In some embodiments of the present application, the tensile strength of the composite binder is from 1000 MPa to 3100 MPa.

[0041] As used herein, the term "tensile strength" represents the critical value at which a sample transitions from uniform plastic deformation to local concentrated plastic deformation, and the tensile strength characterizes the resistance of the material to the maximum uniform plastic deformation. The tensile strength testing method provided by some embodiments of the present application includes: loading the binder sample into a mold with a fixed area (width 10 mm and length 100 mm), drying it to prepare a film with a thickness of 2 mm to 3 mm, and taking a uniformly middle part in the length direction to obtain a sample strip with an area of 10 mm x 30 mm. Using a high-speed tensile testing machine (AL-3000) to test the stress-strain curve of the sample strip, the tensile speed is 50 mm / min, three groups of parallel samples are tested each time, and the average value of the maximum stress when the stress-strain curve of the sample strip cannot present a uniform linear curve is recorded as the tensile strength.

[0042] In some embodiments, the weight ratio of the polymer binder to the fiber reinforcement is from 1:10 to 50:1. In some other embodiments, the weight ratio of the polymer binder to the fiber reinforcement is approximately, for example, about 1:10, about 1:5, about 1:1, about 10:1, about 50:1, or a range formed by any two of these values. In some other embodiments, the weight ratio of the polymer binder to the fiber reinforcement is from 1:6 to 40:1.

[0043] In some embodiments, the method for preparing the composite binder provided in the present application is to uniformly mix a fixed weight ratio of the polymer binder and the fiber reinforcement. It should be understood that for the method for preparing the composite binder in the embodiments of the present application, without departing from the spirit of the present application, other preparation methods that can achieve the functions of the present application can be selected according to specific needs, and are not limited thereto.

[0044] According to another aspect of the present application, embodiments of the present application provide an electrochemical device, which includes a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes the composite binder in the above embodiments. In some embodiments, the electrochemical device is a lithium-ion battery.

[0045] In some embodiments, the negative electrode current collector can be a copper foil or a nickel foil. However, other negative electrode current collectors that can achieve the functions of the present application can be used, and are not limited thereto.

[0046] The negative electrode active material layer includes a negative electrode active material that can absorb and release lithium (Li) (hereinafter, sometimes referred to as "negative electrode active material capable of absorbing / releasing lithium Li"). Examples of materials that can absorb / release lithium (Li) can include carbon-based materials, metal compounds, oxides, sulfides, nitrides of lithium such as LiN3, lithium metal, metals that form alloys with lithium, and polymer materials. In some embodiments, among the materials that can absorb / release lithium (Li), examples of materials with particularly high energy density include elemental silicon, tin, germanium, antimony, bismuth, and elemental, alloy, or compound of aluminum.

[0047] For example, the theoretical specific capacity of silicon is as high as 4200 mAh / g, which is more than ten times that of the traditional graphite negative electrode (the theoretical specific capacity of graphite is 372 mAh / g). In some embodiments of the present application, the negative electrode active material layer further includes a silicon-based material and a carbon-based material.

[0048] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon oxide, silicon alloy, and silicon carbide. In some embodiments, the silicon oxide is at least one of the compounds represented by the general formula SiOx, where x = 0.5 - 1.5, and the silicon oxide includes crystalline, amorphous, or a combination of the two.

[0049] In some embodiments, the carbon-based material comprises at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon, and hard carbon.

[0050] In some embodiments, the ratio of the weight of the carbon-based material to the weight of the silicon-based material is greater than 0 and less than or equal to 99.

[0051] In some embodiments, based on the total weight of the negative electrode active material, the weight ratio of the composite binder is 1% to 20%. In other embodiments, based on the total weight of the negative electrode active material, the weight ratio of the composite binder is approximately, for example, about 1%, about 2%, about 3%, about 4%, about 5%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 20%, or a range composed of any two of these values.

[0052] In some embodiments, the negative electrode active material layer further comprises a dispersant, which is a material soluble in an aqueous solution, and the dispersant comprises at least one of carboxymethyl cellulose and its salts, hydroxyethyl cellulose and its salts, hydroxypropyl cellulose and its salts, polyethylene glycol, and polyvinylpyrrolidone.

[0053] In some embodiments, based on the total weight of the negative electrode active material layer, the weight of the dispersant is less than about 2%. In other embodiments, based on the total weight of the negative electrode active material layer, the weight of the dispersant is less than about 1%.

[0054] In some embodiments, the negative electrode active material layer further comprises a conductive agent, and the conductive agent comprises at least one of conductive carbon black, Ketjen black, graphene, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers. It should be understood that without departing from the spirit of the present application, other conductive agents capable of realizing the functions of the present application can be selected according to specific needs, without being limited thereto.

[0055] In some embodiments, based on the total weight of the negative electrode active material layer, the weight of the conductive agent is less than about 2%. In other embodiments, based on the total weight of the negative electrode active material layer, the weight of the conductive agent is less than about 1%.

[0056] In some embodiments, the positive electrode comprises a positive electrode current collector. The positive electrode current collector can be aluminum foil or nickel foil. However, other positive electrode current collectors capable of realizing the functions of the present application can be used, without being limited thereto.

[0057] In some embodiments, the positive electrode includes a positive electrode active material layer. The positive electrode active material layer includes a positive electrode active material capable of absorbing and releasing lithium (Li) (hereinafter, sometimes referred to as "positive electrode active material capable of absorbing / releasing lithium Li"). Examples of the positive electrode active material capable of absorbing / releasing lithium (Li) may include one or more of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium iron phosphate, lithium titanate, and lithium-rich manganese-based materials.

[0058] Among the above positive electrode active materials, the chemical formula of lithium cobaltate may be Li y Co a M1 b O 2-c , where M1 represents at least one selected from nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), yttrium (Y), lanthanum (La), zirconium (Zr), and silicon (Si), and the values of y, a, b, and c are respectively in the following ranges: 0.8 ≤ y ≤ 1.2, 0.8 ≤ a ≤ 1, 0 ≤ b ≤ 0.2, -0.1 ≤ c ≤ 0.2;

[0059] Among the above positive electrode active materials, the chemical formula of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate may be Li z Ni d M2 e O 2-f , where M2 represents at least one selected from cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), zirconium (Zr), and silicon (Si), and the values of z, d, e, and f are respectively in the following ranges: 0.8 ≤ z ≤ 1.2, 0.3 ≤ d ≤ 0.98, 0.02 ≤ e ≤ 0.7, -0.1 ≤ f ≤ 0.2;

[0060] Among the above positive electrode active materials, the chemical formula of lithium manganate is Li u Mn 2-g M 3g O 4-h, where M3 represents at least one selected from cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W), and the values of z, g, and h are respectively in the following ranges: 0.8 ≤ u ≤ 1.2, 0 ≤ g < 1.0, and -0.2 ≤ h ≤ 0.2.

[0061] In some embodiments, the positive electrode active material layer can further include at least one of a binder and a conductive agent. It should be understood that those skilled in the art can select other binders and conductive agents that can achieve the functions of this application according to actual needs, without being limited thereto.

[0062] In some embodiments, the separator includes, but is not limited to, at least one selected from polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid. For example, polyethylene includes at least one component selected from high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have a good effect on preventing short circuits and can improve the stability of the battery through the shut-off effect. In some embodiments, the separator is polypropylene, and polypropylene has good affinity with the above-mentioned high molecular polymers, which is beneficial to improving the adhesion between the adhesive layer and the separator.

[0063] The lithium-ion battery of this application further includes an electrolyte, and the electrolyte can be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution. The electrolyte solution includes a lithium salt and a non-aqueous solvent.

[0064] In some embodiments, the lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. For example, the lithium salt LiPF6 is selected because it can give a high ionic conductivity and improve the cycling performance.

[0065] The non-aqueous solvent can be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.

[0066] The above-mentioned carbonate compound can be a linear carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0067] Examples of such other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.

[0068] In some embodiments, the non-aqueous solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene sulfite, methyl acetate, ethyl propionate, fluoroethylene carbonate, and combinations thereof.

[0069] It should be understood that, without departing from the spirit of the present application, the preparation methods of the positive electrode, negative electrode, separator, and electrolyte in the embodiments of the present application can be selected according to specific needs to other preparation methods that can achieve the functions of the present application, and are not limited thereto. In one embodiment of the method for manufacturing an electrochemical device, the preparation method of a lithium-ion battery includes: winding, folding, or stacking the negative electrode, separator, and positive electrode in the above embodiments in sequence to form an electrode assembly, placing the electrode assembly into, for example, an aluminum plastic film, injecting an electrolyte, and then performing processes such as vacuum packaging, standing, formation, and shaping to obtain a lithium-ion battery.

[0070] Although the above has been illustrated by way of a lithium-ion battery, those skilled in the art, after reading the present application, can conceive that the adhesive layer of the present application can be used in other suitable electrochemical devices. Such electrochemical devices include any device that undergoes an electrochemical reaction, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0071] Some embodiments of the present application further provide an electronic device, which includes the electrochemical device in the embodiments of the present application.

[0072] The electronic device of the embodiments of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset stereo earphone, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor, etc. Specific Embodiments

[0074] The following are some specific examples and comparative examples, and the cohesive force of their negative electrodes is tested respectively, and the cycle performance and cycle thickness expansion rate of their electrochemical devices (lithium-ion batteries) are tested to better illustrate the technical solutions of the present application.

[0075] I. Test methods

[0076] 1.1 Cohesive force test:

[0077] In a dry room environment, disassemble the formed lithium-ion batteries in the following examples to obtain complete negative electrodes, let them stand for 5 minutes until the electrolyte evaporates completely, cut the negative electrodes into pieces of 80 mm × 30 mm, use a high-speed tensile testing machine (AL-3000), and set the tensile speed to 50 mm / min and the tensile displacement to 50 mm to conduct the cohesive force test. From the following examples, take 4 lithium-ion batteries in each group and calculate the average cohesive force of the negative electrodes of the lithium-ion batteries.

[0078] 1.2 Cycle performance test:

[0079] Place the formed lithium-ion batteries in the following examples and comparative examples in a constant temperature oven at 25°C ± 2°C and let them stand for 2 hours, charge at a constant current of 0.7C to 4.45V, then charge at a constant voltage of 4.45V to 0.05C and let it stand for 15 minutes; then discharge at a constant current of 0.5C to 3.0V. This is one charge-discharge cycle process, and record the discharge capacity of the first cycle of the lithium-ion battery; then repeat the above method for 200 charge-discharge cycle processes, and record the discharge capacity after 200 cycles.

[0080] Take 4 lithium-ion batteries in each group and calculate the average value of the capacity retention rate of the lithium-ion batteries. The cycle capacity retention rate of the lithium-ion battery = discharge capacity (mAh) after the 200th cycle / discharge capacity (mAh) after the first cycle × 100%.

[0081] 1.3 Cycle thickness expansion rate test:

[0082] Use a 600g flat thickness gauge (ELASTOCON, EV 01) to measure the thickness of the lithium-ion battery.

[0083] The formed lithium-ion batteries of the following examples and comparative examples were placed in a thermostatic chamber at 25°C ± 2°C and left standing for 2 hours. They were charged at a constant current of 0.7C to 4.45V, then charged at a constant voltage of 4.45V to 0.05C and left standing for 15 minutes, and the thickness of the lithium-ion batteries in the fully charged state was recorded; then they were discharged at a constant current of 0.5C to 3.0V, which was a single charge-discharge cycle process, and the thickness of the lithium-ion batteries in the first cycle was recorded; then the charge-discharge cycle process was repeated 200 times according to the above method, and the thickness of the lithium-ion batteries after 200 cycles was recorded.

[0084] Four lithium-ion batteries were taken from each group, and the average value of the cyclic thickness expansion rate of the lithium-ion batteries was calculated. The cyclic thickness expansion rate of the lithium-ion battery = (the thickness of the lithium-ion battery in the 200th cycle / the thickness of the lithium-ion battery in the first cycle - 1) × 100%.

[0085] II. Preparation method

[0086] 2.1 Preparation of the positive electrode

[0087] Lithium cobaltate, conductive carbon black, and polyvinylidene fluoride were dissolved in an N-methylpyrrolidone (NMP) solution in a weight ratio of 97:1.4:1.6 to form a positive electrode slurry. Aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was coated on the positive electrode current collector. After drying, cold pressing, and cutting procedures, the positive electrode was obtained.

[0088] 2.2 Preparation of the negative electrode

[0089] According to the negative electrode formula in Table 1-1 and Table 2-1 below, they were mixed and dissolved in deionized water to form a negative electrode slurry. Copper foil was used as the negative electrode current collector, and the negative electrode slurry was coated on the negative electrode current collector. After drying, cold pressing, and cutting procedures, the negative electrode was obtained.

[0090] 2.3 Preparation of the electrolyte

[0091] In an environment with a water content of less than 10 ppm, lithium hexafluorophosphate and a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): vinylene carbonate (VC) = 20; 30; 20; 28; 2, by weight) were formulated in a weight ratio of 8:92 to form an electrolyte.

[0092] 2.4 Preparation of the lithium-ion battery

[0093] A polyethylene film is used as the separator. The above-mentioned positive electrode, separator, and negative electrode are stacked in sequence, with the separator in the middle between the positive and negative electrodes to play a separating role, and then wound into an electrode assembly. Subsequently, the electrode assembly is placed in an aluminum-plastic film packaging bag, and after removing moisture at 80°C, a dry electrode assembly is obtained. Then, the above-mentioned electrolyte is injected into the dry electrode assembly, and through processes such as vacuum packaging, standing, formation, and shaping, the preparation of the lithium-ion batteries in the following examples and comparative examples is completed.

[0094] III. Examples and Comparative Examples

[0095] 3.1 Carbon-based material negative electrode

[0096] Examples 1-1 to 1-16 and Comparative Examples 1-1 to 1-9 are lithium-ion batteries using carbon-based materials as the negative electrode, and the negative electrode formulations are shown in Table 1-1. Although the weight ratios of the polymer binder and the fiber reinforcement in the binders of Examples 1-1, 1-10 and Comparative Examples 1-8 and 1-9 are the same, other parameters of the binder such as solid content, particle size, aspect ratio of the fiber reinforcement, and tensile strength are adjusted. For details, please refer to Table 1-2.

[0097] Table 1-1

[0098]

[0099]

[0100] Table 1-2 shows the solid content, particle size, and tensile strength of the composite binder of the above examples and comparative examples, as well as the aspect ratio of the fiber reinforcement and the molecular weight of the polymer binder.

[0101] Table 1-2

[0102]

[0103]

[0104] After formation, the thickness, width, length, and weight of the lithium-ion batteries containing the negative electrode in Table 1-1 are measured. Subsequently, some of the formed lithium-ion batteries are disassembled, the negative electrodes are tested for cohesive force, and another part of the lithium-ion batteries are tested for cycle performance and cycle thickness expansion rate, and the test results are recorded.

[0105] The negative electrodes of Examples 1-1 to 1-16 and Comparative Examples 1-1 to 1-9 are tested for cohesive force, and the lithium-ion batteries containing the negative electrode are tested for cycle performance and cycle thickness expansion rate. The test results are shown in Table 1-3.

[0106] Table 1-3

[0107]

[0108]

[0109] As shown in Tables 1-1 to 1-3, by comparing Example 1-1 with Comparative Examples 1-1 to 1-3, it can be seen that under the same weight ratio composition, the lithium-ion battery of the embodiment of the present application can effectively increase the internal cohesion of the negative electrode to more than 40 N / m by adding a composite binder to the negative electrode, thereby reducing the cyclic thickness expansion rate of the lithium-ion battery and improving its cyclic capacity retention rate. As shown in Comparative Examples 1-2 and 1-3, when any component in the composite binder is used alone as a binder, the internal cohesion of the negative electrode cannot reach more than 30 N / m, the cyclic thickness expansion rate is relatively high, and the cyclic capacity retention rate is relatively low. By comparing the examples and comparative examples, it can be seen that the embodiments within the ratio range of the polymer binder and the fiber reinforcement provided in the present application have better cyclic capacity retention rate and lower thickness expansion rate. Excessive ratio of the polymer binder or the fiber reinforcement will cause the cyclic performance of the battery to decrease.

[0110] By comparing Examples 1-1 to 1-3, it can be seen that under different carbon-based material ratios, the lithium-ion batteries of the embodiments of the present application all have a certain internal cohesion and can effectively reduce the cyclic thickness expansion rate, so that the cyclic capacity retention rate of the lithium-ion battery remains at a relatively high level.

[0111] By comparing Examples 1-1 and 1-5 to 1-9, it can be seen that the composite binders composed of different polymer binders and fiber reinforcements provided in the present application can all improve the internal cohesion of their lithium-ion batteries. In particular, the copolymer of polyacrylic acid and alginic acid can increase the internal cohesion of the negative electrode to more than 70 N / m.

[0112] By comparing Examples 1-1, 1-15 and 1-16 with Comparative Examples 1-6 and 1-7, it can be seen that when the weight ratio of the composite binder in the negative electrode is too low, it will cause a significant decrease in the internal cohesion of the negative electrode, thereby causing an increase in the cyclic thickness expansion rate; on the contrary, when the weight ratio of the composite binder in the negative electrode is too high, although it can still inhibit the cyclic expansion rate of the negative electrode, it will cause a decrease in the cyclic capacity retention rate of the electrochemical device, resulting in a decrease in the cyclic performance of the electrochemical device.

[0113] 3.2 Silicon-based material negative electrode

[0114] Examples 2-1 to 2-21 and Comparative Examples 2-1 to 2-10 are lithium-ion batteries using carbon-based materials and silicon-based materials as the negative electrode. The negative electrode formulations are shown in Table 2-1. Among them, although the types and weight ratios of the polymer binder and the fiber reinforcement in the binder of Examples 2-9 and 2-13 to 2-21 are the same, other parameters of the binder such as solid content, particle size, aspect ratio of the fiber reinforcement, and tensile strength are adjusted. For details, please refer to Table 2-2.

[0115] Table 2-1

[0116]

[0117]

[0118] Table 2-2 shows the solid content, particle size, and tensile strength of the composite binder of the above examples and comparative examples, as well as the molecular weight of the polymer binder and the length and diameter of the fiber reinforcement.

[0119] Table 2-2

[0120]

[0121]

[0122] The thickness, width, length, and weight of the formed lithium-ion batteries containing the negative electrode in Table 2-1 were measured. Subsequently, some of the formed lithium-ion batteries were disassembled, the cohesive force of their negative electrodes was tested, and the cycle performance test and the cycle thickness expansion rate test were carried out on another part of the lithium-ion batteries, and the test results were recorded.

[0123] The cohesive force of the negative electrodes of Examples 2-1 to 2-21 and Comparative Examples 2-1 to 2-10 was tested, and the cycle performance test and the cycle thickness expansion rate test were carried out on the lithium-ion batteries containing the negative electrode. The test results are shown in Table 2-3.

[0124] Table 2-3

[0125]

[0126]

[0127] As shown in Tables 2-1 and 2-3, by comparing Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-3, it can be seen that under the same weight ratio composition, the composite binder of the present application can also improve the cycle capacity retention rate and reduce the cycle thickness expansion rate of the electrochemical device using a silicon-based material anode. Compared with the binder added alone, the composite binder of the polymer binder and the fiber reinforcement provided by the present application can effectively improve the cohesion of the anode, thereby reducing the cycle thickness expansion rate of the lithium-ion battery and increasing its cycle capacity retention rate.

[0128] Referring to Tables 2-2 and 2-3, by comparing Examples 2-9, 2-13, 2-14 and 2-15 with Comparative Examples 2-4, 2-5 and 2-6, it can be seen that when the solid content of the composite binder used is in the range of 1% to 60%, the tensile strength of the binder can be effectively improved, and as the tensile strength increases, the cohesion of the composite binder will also increase.

[0129] By comparing Examples 2-9, 2-16, 2-17 and 2-18 with Comparative Examples 2-7 and 2-8, it can be seen that when the molecular weight of the polymer binder in the composite binder used is in the range of 100 kDa to 10,000 kDa, the tensile strength of the binder can be effectively improved.

[0130] By comparing Examples 2-9, 2-19, 2-20 and 2-21 with Comparative Examples 2-9 and 2-10, it can be seen that the composite binder provided by the examples of the present application can maintain a certain tensile strength to further improve the cohesion of the anode containing it.

[0131] Through the comparison of the above examples, it can be clearly understood that the composite binder of the present application as an additive for the anode can effectively improve the cohesion of the anode and inhibit the volume expansion rate of the anode, so that the structure of the anode remains stable. In addition, by limiting the composition ratio of the anode of the electrochemical device of the present application, the ion circulation channels of the anode can be optimized, thereby significantly improving the safety performance and cycle performance of the electrochemical device.

[0132] References throughout this specification to "some embodiments", "part of embodiments", "an embodiment", "another example", "example", "specific example", or "partial example" mean that at least one embodiment or example in this application includes the specific features, structures, materials, or characteristics described in that embodiment or example. Thus, descriptions that appear throughout this specification, such as "in some embodiments", "in embodiments", "in an embodiment", "in another example", "in an example", "in a specific example", or "example" do not necessarily refer to the same embodiment or example in this application. In addition, the specific features, structures, materials, or characteristics herein may be combined in any suitable manner in one or more embodiments or examples.

[0133] Although the illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on this application, and that changes, substitutions, and modifications to the embodiments can be made without departing from the spirit, principles, and scope of this application.

Claims

1. An electrochemical device, comprising: a positive electrode; a separator; and a negative electrode, the negative electrode comprising: a negative current collector; and a negative active material layer, wherein the negative active material layer comprises a composite binder, wherein the composite binder comprises: a polymer binder, wherein the polymer binder is a solution-type binder comprising a homopolymer or a copolymer, the monomer of the homopolymer being acrylic acid or alginic acid, and the monomers of the copolymer being acrylic acid and alginic acid; and a fiber reinforcement composed of polyvinyl alcohol fibers; wherein the particle size Dv50 of the composite binder is 1 μm to 100 μm, wherein, based on the total weight of the negative active material layer, the weight ratio of the composite binder is 1% to 20%.

2. The electrochemical device according to claim 1, wherein the fiber reinforcement has a length of 5 μm to 100 μm, a diameter of 0.001 μm to 1.0 μm, and an aspect ratio of 100 to 10,000.

3. The electrochemical device according to claim 1, wherein the weight-average molecular weight of the polymer binder is 100 kDa to 10,000 kDa.

4. The electrochemical device according to claim 1, wherein the weight ratio of the polymer binder to the fiber reinforcement is 1:10 to 50:

1.

5. The electrochemical device according to claim 1, wherein the composite binder is an aqueous solution and the solid content of the composite binder is 1% to 60%.

6. The electrochemical device according to claim 1, wherein the negative active material layer further comprises at least one of a silicon-based material and a carbon-based material, wherein the silicon-based material comprises at least one of elemental silicon, silicon oxide, silicon alloy, and silicon carbide, and the carbon-based material comprises at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon, and hard carbon.

7. The electrochemical device according to any one of claims 1 to 6, wherein the negative active material layer further comprises a dispersant, and based on the total weight of the negative active material layer, the weight of the dispersant is less than 2%.

8. The electrochemical device according to any one of claims 1 to 6, wherein the negative active material layer further comprises a conductive agent, and based on the total weight of the negative active material layer, the weight of the conductive agent is less than 2%.

9. An electronic device comprising the electrochemical device according to any one of claims 1 to 8.

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