Negative electrode sheet, cell, battery and electric device

Abstract

Provided in the embodiments of the present invention are a negative electrode sheet, a cell, a battery and an electric device. The negative electrode sheet comprises a negative current collector and a negative electrode film layer arranged on at least one side of the negative current collector, wherein the negative electrode film layer comprises a negative electrode active material and a binder, the negative electrode active material comprising a silicon-based material, and the binder comprising at least one of the following functional groups: a hydroxyl group, a carboxyl group, an amino group, a cyano group, an ester group and a vinyl group. The technical solution of the present application can improve the cohesive force and bonding force of the negative electrode sheet, thereby reducing the shedding and stripping of the electrode sheet during a production process, and therefore the cycle performance of a battery is improved.

Description

Negative electrode sheet, battery cell, battery and electrical device

[0001] Cross-references

[0002] This application claims priority to the Chinese application filed with the Patent Office of China on June 30, 2023, with application number 202310796969.3 and invention name “Negative electrode sheet, battery cell, battery and electrical device”, all contents of which are incorporated into this application by application. Technical Field

[0003] The present application relates to the field of battery technology, and more specifically, to a negative electrode sheet, a battery cell, a battery, and an electrical device. Background Art

[0004] In recent years, lithium-ion batteries have been used in an increasingly diverse range of applications, including energy storage and power supply applications such as wind, hydro, thermal, and solar power plants, as well as in electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. This significant advancement in lithium-ion batteries has also led to higher demands on their performance across various aspects.

[0005] Therefore, how to improve the cycle performance of lithium-ion batteries is an urgent problem to be solved.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode plate, a battery cell, a battery and an electrical device to improve the cycle performance of the battery.

[0008] In a first aspect, a negative electrode plate is provided, comprising a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector; the negative electrode film layer comprises a negative electrode active material and a binder, and the negative electrode active material comprises a silicon-based material; wherein the binder comprises at least one of the following functional groups: hydroxyl, carboxyl, amino, cyano, lipid, and vinyl.

[0009] In an embodiment of the present application, the negative electrode sheet includes a negative electrode film layer; the negative electrode film layer includes a negative electrode active material and a binder, wherein the negative electrode active material includes a silicon-based material. The binder includes at least one functional group selected from the group consisting of hydroxyl, carboxyl, amino, cyano, lipid, and vinyl groups. By adding silicon-based materials and binders to the negative electrode film layer, on the one hand, the theoretical specific capacity of the silicon-based material is higher, which is beneficial to improving the energy density of the battery; on the other hand, the silicon-based material is relatively hard and not easily crushed when cold pressed, and the particle shape is relatively irregular, and there are certain gaps between the particles. Therefore, the negative electrode sheets containing silicon-based materials generally have a larger porosity, and the binders containing at least one functional group of hydroxyl, carboxyl, amino, cyano, lipid, and vinyl have better adhesion. Adding a binder with better adhesion to the negative electrode film layer so that the binder is filled in the large pores of the silicon-based material can improve the cohesion of the negative electrode sheet and the adhesion between the negative electrode film layer and the negative electrode current collector, so as to inhibit the serious volume expansion of the silicon-based material during the battery cycle and reduce the demolding and powder loss of the negative electrode sheet, thereby improving the cycle performance of the battery.

[0010] In one possible embodiment, the volume average particle size Dv50 of the binder is 0.1 μm-0.8 μm; optionally, the volume particle size distribution Dv50 of the binder is 0.3 μm-0.7 μm; optionally, the volume average particle size Dv50 of the binder is 0.35 μm-0.45 μm.

[0011] In the embodiment of the present application, in order to improve the bonding and cohesion of the negative electrode sheet and improve the demolding and powder shedding of the sheet, a binder containing at least one functional group selected from hydroxyl, carboxyl, amino, cyano, lipid, and vinyl groups is added to the negative electrode film layer to fill the larger gaps in the silicon-based material. In addition, by making the volume average particle size Dv50 of the binder 0.1μm-0.8μm, further, 0.3μm-0.7μm, and further, 0.35μm-0.45μm, the binder with a moderate particle size is filled in the larger gaps in the silicon-based material, which can enhance the cohesion between the negative electrode active materials and the bonding between the negative electrode active materials and the negative electrode current collector, thereby further reducing the demolding and powder shedding of the sheet and improving the cycle stability of the battery.

[0012] In one possible implementation, the volume average particle size Dv50 of the binder is 0.5 μm-0.7 μm.

[0013] In the embodiments of this application, to enhance the bonding strength of the negative electrode sheet and improve sheet release and powder shedding, a binder containing at least one functional group selected from hydroxyl, carboxyl, amino, cyano, lipid, and vinyl groups is added to the negative electrode film layer to fill the larger gaps in the silicon-based material. Furthermore, by setting the binder's volume average particle size (Dv50) to 0.5 μm-0.7 μm, the bonding strength of the negative electrode sheet can be enhanced, reducing sheet release and powder shedding, and improving the battery's cycling stability.

[0014] In a possible implementation manner, the cross-linking degree of the binder is 50-100. Optionally, the cross-linking degree of the binder is 80-98.

[0015] In the embodiments of the present application, if the binder has a high degree of crosslinking, it absorbs less electrolyte, which in turn slows the formation of the negative electrode slurry and increases the strength of the binder. Therefore, by maintaining the binder's degree of crosslinking between 50-100, and particularly between 80-98, the binder's strength and electrolyte resistance can be improved. Maintaining high binder strength helps suppress negative electrode expansion and improves the bonding between the active materials in the negative electrode sheet, thereby reducing the probability of powder loss and demolding of the negative electrode sheet.

[0016] In a possible implementation manner, the swelling rate of the binder is 5%-80%. Optionally, the swelling rate of the binder is 10%-50%.

[0017] In the embodiments of this application, the binder typically swells. If this swelling exceeds a certain level, it can affect the conductivity and adhesion between the active material and the current collector, further impacting battery capacity and cycle performance. Therefore, by limiting the binder's swelling rate to 5%-80%, particularly 10%-50%, a binder with a moderate swelling rate can achieve better bonding, further reducing the probability of powder loss and mold release from the negative electrode sheet.

[0018] In a possible implementation manner, the glass transition temperature of the binder is -20°C-60°C. Optionally, the glass transition temperature of the binder is -10°C-40°C.

[0019] In the embodiments of this application, if the glass transition temperature is too high, it will affect the brittleness of the negative electrode sheet, which may lead to the negative electrode sheet releasing and powdering during battery cycling. Therefore, by maintaining the glass transition temperature of the binder between -20°C and 60°C, especially between -10°C and 40°C, the brittleness of the negative electrode sheet can be further reduced.

[0020] In a possible implementation manner, the elongation of the adhesive is 50%-400%. Optionally, the elongation of the adhesive is 100%-200%.

[0021] In the embodiments of the present application, a binder with a certain elongation can inhibit the expansion of the negative electrode during repeated expansion, thereby reducing cracking or powder loss of the electrode. By setting the binder's elongation to 50%-400%, particularly 100%-200%, the binder can have strong deformation resistance.

[0022] In a possible implementation, based on 100 parts by weight of the negative electrode film layer, the weight of the binder is 1 part by weight to 10 parts by weight. Optionally, the weight of the binder is 2 parts by weight to 8 parts by weight.

[0023] In the examples of this application, to reduce mold release and powder loss during negative electrode sheeting, a binder containing specific functional groups is added to the negative electrode film layer, allowing the binder to fill the larger pores within the negative electrode active material. By setting the binder content in the negative electrode film layer to 1%-10%, particularly 4%-8%, the adhesive strength between the negative electrode active materials is enhanced, thereby suppressing volume expansion of the negative electrode sheet, while also reducing the reduction in battery energy density caused by excessive binder content.

[0024] In a possible embodiment, the binder includes at least one of styrene-butadiene and its modifications, styrene-acrylic and its modifications, polyurethane and its modifications, polyvinylidene fluoride and its modifications, and acrylate and its modifications.

[0025] In the embodiments of the present application, by using at least one of styrene butadiene and its modified products, styrene acrylic and its modified products, polyurethane and its modified products, polyvinylidene fluoride and its modified products, and acrylate and its modified products with good bonding strength as a binder, it helps to further improve the bonding strength between the negative electrode active material and the negative electrode current collector.

[0026] In a possible embodiment, the silicon-based material includes at least one of a silicon-oxygen material and a silicon-carbon material; optionally, the silicon-oxygen material includes SiO x , wherein 0.4≤x≤1.6; optionally, the silicon-carbon material includes a silicon-carbon composite, and based on the total mass of the silicon-carbon composite, the ratio of the mass content B of the carbon element to the mass content A of the silicon element in the silicon-carbon composite is 1.3≤B / A≤2.

[0027] In the embodiment of the present application, by adding silicon-based materials, especially silicon-oxygen materials or silicon-carbon materials, to the negative electrode active material, it is beneficial to improve the energy density of the battery. The silicon-oxygen materials in the silicon-based materials not only have high theoretical capacity and excellent stability, but also have the advantages of low cost, non-toxicity and environmental friendliness; silicon-carbon materials have high theoretical capacity and good cycle performance. By using silicon-oxygen materials, especially SiO x, wherein 0.4≤x≤1.6, or using a silicon-carbon material in which the ratio of the mass proportion of silicon element to the silicon-carbon composite A and the mass proportion of carbon element to the silicon-carbon composite B is 1.3≤B / A≤2, can further improve battery performance.

[0028] In one possible embodiment, the negative electrode active material further includes graphite; wherein, based on 100 parts by weight of the negative electrode film layer, the weight of the graphite is 45 parts by weight to 70 parts by weight, optionally, the weight of the graphite is 55 parts by weight to 65 parts by weight.

[0029] In the embodiments of this application, silicon-based materials have high theoretical capacity but poor electrical conductivity. Therefore, if silicon-based materials are used alone as the negative electrode active material, the battery's electrical conductivity will be very poor. By adding graphite, which has high electrical conductivity, to the negative electrode active material and ensuring that the mass proportion of graphite in the negative electrode film is 45%-70%, particularly 55%-65%, good battery cycling performance can be maintained.

[0030] In one possible embodiment, the compaction density of the negative electrode sheet is 1.0 g / cm 3 -2.5g / cm 3 Optionally, the compaction density of the negative electrode is 1.2 g / cm 3 -1.8g / cm 3 .

[0031] In the embodiment of the present application, the compaction density of the negative electrode sheet is set to 1.0 g / cm 3 -2.5g / cm 3 , especially 1.2g / cm 3 -1.8g / cm 3 , which can further improve the energy density of the battery.

[0032] In a possible implementation, the thickness of the negative electrode plate is 60 μm-150 μm. Optionally, the thickness of the negative electrode plate is 90 μm-130 μm.

[0033] In the embodiment of the present application, the energy density of the battery can be further improved by making the thickness of the negative electrode sheet 60 μm-150 μm, particularly 90 μm-130 μm.

[0034] The second aspect of the present application provides a battery cell, comprising the negative electrode plate described in any embodiment of the first aspect of the present application.

[0035] In a possible embodiment, the battery cell further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0036] In one possible embodiment, the positive electrode active material includes Li x (Ni a Co b Mn c ) 1-d M d O 2- y A y , wherein M includes at least one of Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, 0.2<x≤1.2, 0.5≤a<1.0, 0≤b<0.5, 0≤c<1, 0≤d<1, and 0≤y<0.02.

[0037] A third aspect of the present application provides a battery, comprising the battery cell described in the second aspect of the present application.

[0038] The fourth aspect of the present application provides an electrical device comprising the battery according to the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0040] FIG1 is a schematic structural diagram of a negative electrode sheet according to an embodiment of the present application;

[0041] FIG2 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0042] FIG3 is a schematic structural diagram of a battery cell according to an embodiment of the present application;

[0043] FIG4 is a schematic diagram of a battery according to an embodiment of the present application;

[0044] FIG5 is a schematic structural diagram of a battery according to an embodiment of the present application;

[0045] FIG6 is a schematic structural diagram of an electrical device according to an embodiment of the present application. DETAILED DESCRIPTION

[0046] The following describes in detail embodiments of the negative electrode sheet, battery cell, battery, and electrical device of the present application, with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0047] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of specific range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0050] Unless otherwise specified, all steps of the present application may be performed sequentially, randomly, or optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0051] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or comprised.

[0052] The terms "above", "below", "greater than" or "less than" as used in this application are inclusive of the number, for example, "at least one" means one or more, and "at least one of A and B" means "A", "B" or "A and B".

[0053] Lithium-ion batteries are widely used in consumer electronics due to their high energy density, power, and long cycle life. In recent years, with the continuous development of electric vehicles and energy storage systems, people's requirements for battery cycle performance and other aspects have also been continuously increasing.

[0054] At a time when the capacity of lithium-ion batteries using graphite-based materials as negative electrode active materials is gradually failing to meet the long-range requirements of electric vehicles, silicon-based materials have become the most promising next-generation lithium-ion battery negative electrode materials due to their advantages such as large specific capacity, low discharge platform, and rich energy storage. However, silicon-based materials have serious limitations in their commercial application due to their own factors. First, silicon-based materials experience severe volume expansion during battery cycling. The large volume change during lithium insertion and removal can easily lead to particle pulverization and active material falling off the current collector, ultimately causing powder loss, severe demolding, and poor cycle performance of the pole pieces. Therefore, how to reduce powder loss and demolding in batteries using silicon-based materials, thereby achieving better cycle performance, is an urgent problem that needs to be solved.

[0055] In view of this, the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector. By adding a silicon-based material and a binder to the negative electrode active material of the negative electrode film layer, and making the binder include at least one of hydroxyl, carboxyl, amino, cyano, lipid, and vinyl groups, the binder with good bonding force is filled in the large pores of the silicon-based material, thereby suppressing the poor bonding force between the negative electrode active materials caused by the severe volume expansion of the silicon-based material during the battery cycle, thereby alleviating the powdering and demolding phenomena of the plate, and having better cycle performance.

[0056] The negative electrode sheet, battery cell, battery and electrical device of the present application are described below with reference to the accompanying drawings.

[0057] In addition, the technical solution of the present application is applicable to various types of batteries such as lithium-ion batteries, lithium metal batteries, sodium-ion batteries, etc., and the present application does not limit this; for the convenience of description, the following description will take lithium-ion batteries as an example.

[0058] [Negative electrode]

[0059] The first aspect of the present application provides a negative electrode sheet. Figure 1 is a schematic structural diagram of a negative electrode sheet according to one embodiment of the present application. As shown in Figure 1 , the negative electrode sheet 121 includes a negative electrode current collector 122 and a negative electrode film layer 123 disposed on at least one side of the negative electrode current collector 122. The negative electrode film layer 123 includes a negative electrode active material and a binder. The negative electrode active material includes a silicon-based material. The binder includes at least one of the following functional groups: hydroxyl, carboxyl, amino, cyano, lipid, and vinyl.

[0060] Adding silicon-based materials and binders to the negative electrode film layer 123, and making the binder include at least one functional group selected from hydroxyl, carboxyl, amino, cyano, lipid, and vinyl groups, can improve the adhesion and cohesion of the negative electrode sheet to inhibit the expansion of the negative electrode sheet, thereby improving the cycle performance of the battery.

[0061] In the embodiments of the present application, silicon-based materials refer to materials grown through different process steps using silicon materials as substrates or bases, including silicon materials on insulating layers, germanium silicon materials, porous silicon, microcrystalline silicon, and other compound semiconductor materials grown heteroepitaxially using silicon as a base.

[0062] In an embodiment of the present application, an acrylate compound can be introduced into the adhesive so that the adhesive includes a lipid group; that is, the adhesive can include an acrylate compound, wherein the acrylate compound includes at least one of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, and tert-butyl methacrylate.

[0063] In the embodiment of the present application, a multifunctional vinyl compound can be introduced into the binder to make the binder include vinyl groups. That is, the binder can include a multifunctional vinyl compound, the multifunctional vinyl compound includes two or more vinyl groups, and the multifunctional vinyl compound includes at least one of divinylbenzene, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and diallyl phthalate.

[0064] Typically, a battery cell consists of a positive electrode, a separator, a negative electrode, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed from the positive and negative electrodes. The electrolyte transfers ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0065] It should be noted here that the “positive electrode sheet” and “negative electrode sheet” mentioned in the embodiments of the present application refer to the positive electrode sheet and the negative electrode sheet as a whole including active materials, current collectors or other additives.

[0066] The negative electrode sheet 121 includes a negative electrode current collector 122 and a negative electrode film layer 123 disposed on at least one surface of the negative electrode current collector 122 . The negative electrode film layer 123 includes a negative electrode active material.

[0067] As an example, the negative electrode current collector 122 has two opposite surfaces in its thickness direction, and the negative electrode film layer 123 is disposed on either or both of the two opposite surfaces of the negative electrode current collector 122 .

[0068] In the above solution, the negative electrode sheet 121 includes a negative electrode film layer 123. Further, the negative electrode film layer 123 includes a negative electrode active material and a binder. Further, the negative electrode active material includes a silicon-based material. The volume average particle size Dv50 of the binder is 0.3 μm-0.7 μm. By adding silicon-based materials and binders to the negative electrode film layer 123, on the one hand, the theoretical specific capacity of the silicon-based material is higher, which is beneficial to improving the energy density of the battery; on the other hand, the silicon-based material is relatively hard and not easily crushed when cold pressed, and the particle shape is relatively irregular, and there are certain gaps between the particles. Therefore, the negative electrode plate 121 containing silicon-based materials generally has a large porosity, and the binder containing at least one of hydroxyl, carboxyl, amino, cyano, lipid, and vinyl groups has good adhesion. Adding a binder with good adhesion to the negative electrode film layer 123 so that the binder is filled in the large pores of the silicon-based material can improve the cohesion of the negative electrode plate 121 and the adhesion between the negative electrode film layer 123 and the negative electrode current collector 122, so as to inhibit the serious volume expansion of the silicon-based material during the battery cycle and reduce the demolding and powder loss of the negative electrode plate, thereby improving the cycle performance of the battery.

[0069] It should be noted here that “demolding” of the electrode means that the negative electrode film layer 123 partially or completely falls off from the negative electrode current collector 122 ; “powdering” of the electrode means that the negative electrode active material falls off from the negative electrode current collector 122 .

[0070] In some embodiments, the volume average particle size Dv50 of the binder is 0.1 μm-0.8 μm; optionally, the volume average particle size distribution Dv50 of the binder is 0.3 μm-0.7 μm; optionally, the volume average particle size Dv50 of the binder is 0.35 μm-0.45 μm.

[0071] In the above scheme, to improve the bonding strength of the negative electrode plate 121 and improve plate demolding and powder shedding, a binder containing at least one functional group selected from the group consisting of hydroxyl, carboxyl, amino, cyano, lipid, and vinyl groups is added to the negative electrode film layer to fill the larger gaps in the silicon-based material. Furthermore, by setting the binder's volume average particle size (Dv50) to 0.1μm-0.8μm, further to 0.3μm-0.7μm, and even further to 0.35μm-0.45μm, the binder with a moderate particle size can fill the larger gaps in the silicon-based material, enhancing the bonding strength between the negative electrode active materials and between the negative electrode active materials and the negative electrode current collector 122, thereby further reducing plate demolding and powder shedding, and improving the battery's cycling stability.

[0072] It should be noted that the volume average particle size Dv50 of the binder may be 0.1 μm, 0.3 μm, 0.5 μm, 0.6 μm, or any value within the range consisting of the aforementioned values.

[0073] In some embodiments, the volume average particle size Dv50 of the binder is 0.5 μm to 0.7 μm.

[0074] In the above solution, to enhance the bonding strength of the negative electrode sheet 121 and mitigate issues such as sheet demolding and powder shedding, a binder containing at least one of the following functional groups: hydroxyl, carboxyl, amino, cyano, lipid, or vinyl, is added to the negative electrode film 123 to fill the larger gaps within the silicon-based material. Furthermore, by setting the binder's volume average particle size (Dv50) to 0.5 μm-0.7 μm, the bonding strength within the negative electrode sheet 121 is enhanced, minimizing demolding and powder shedding, and improving the battery's cycling stability.

[0075] In some embodiments, the degree of crosslinking of the binder is 50-100. Optionally, the degree of crosslinking of the binder is 80-98.

[0076] The degree of crosslinking is a measure of polymerization reaction and has a significant impact on the binder. A higher degree of crosslinking increases the binder's cohesion, resulting in less liquid absorption, such as the electrolyte in a battery, and slower film formation, increasing the strength of the binder. However, excessive crosslinking can lead to excessive internal cohesion, resulting in poor rheological properties and negatively impacting the battery's fast-charging performance.

[0077] In the above scheme, by maintaining the cross-linking degree of the binder at 50-100, especially 80-98, the strength of the binder and the electrolyte resistance can be improved. Maintaining the high strength of the binder is beneficial to suppressing the expansion of the negative electrode and improving the bonding force between the active materials in the negative electrode sheet 121, thereby reducing the probability of powder loss and demolding of the negative electrode sheet 121.

[0078] It should be noted that the degree of crosslinking of the binder can be 50, 60, 80, 90, or any value within the range of the aforementioned values.

[0079] In some embodiments, the swelling ratio of the binder is 5%-80%. Alternatively, the swelling ratio of the binder is 10%-50%.

[0080] Swelling refers to the change in volume of a binder in a liquid. The swelling rate refers to the degree to which the binder expands when it absorbs the liquid.

[0081] Binders usually swell, but if the swelling exceeds a certain degree, it will affect the strength and bonding performance of the binder, affect the bonding force between the active material and the current collector in the battery, and thus affect various aspects of the battery performance.

[0082] In the above scheme, by limiting the swelling rate of the binder to 5%-50%, especially 10%-30%, the binder with a moderate swelling rate can achieve a better bonding effect and have a higher strength, thereby effectively suppressing the expansion of the negative electrode sheet 121 and further reducing the probability of powder loss and demolding of the negative electrode sheet 121.

[0083] It should be noted that the swelling ratio of the binder can be 5%, 10%, 20%, 40%, or any value within the range of the aforementioned values.

[0084] In some embodiments, the glass transition temperature of the binder is -20°C to 60°C. Alternatively, the glass transition temperature of the binder is -10°C to 40°C.

[0085] The glass transition temperature refers to the temperature at which the glass state transitions to the highly elastic state. If the glass transition temperature is too high, the negative electrode plate 121 may become brittle, which in turn may cause the negative electrode plate 121 to release from the mold and shed powder during battery cycling.

[0086] In the above solution, by maintaining the glass transition temperature of the binder in the range of -20°C to 60°C, particularly -10°C to 40°C, the brittleness of the negative electrode sheet 121 can be further reduced.

[0087] It should be noted that the glass transition temperature of the binder may be -10°C, 10°C, 25°C, 40°C, or any value within the range of the aforementioned values.

[0088] In some embodiments, the elongation of the adhesive is 50%-400%. Alternatively, the elongation of the adhesive is 100%-200%.

[0089] Elongation refers to the percentage of the elongation of the original gauge length to the original gauge length after the material breaks after stretching.

[0090] Regarding the binder, during the repeated expansion of the negative electrode sheet 121 , a binder with a certain elongation can suppress the expansion of the negative electrode sheet 121 , thereby reducing the possibility of the negative electrode sheet 121 being broken or powdered.

[0091] In the above solution, by making the elongation of the adhesive 50%-400%, especially 100%-200%, the adhesive can have stronger anti-deformation performance.

[0092] It should be noted that the elongation of the adhesive may be 50%, 100%, 200%, 350%, or any value within the range of the aforementioned values.

[0093] In some embodiments, based on 100 parts by weight of the negative electrode film layer 123 , the weight of the binder is 1 part by weight to 10 parts by weight. Optionally, the weight of the binder is 2 parts by weight to 8 parts by weight.

[0094] In the above solution, to reduce the demolding and powder loss of the negative electrode sheet 121, a binder with a larger volume average particle size is added to the negative electrode film layer 123, so that the binder fills the larger pores in the negative electrode active material. By setting the binder mass ratio in the negative electrode film layer 123 to 1%-10%, especially 2%-8%, the adhesion between the negative electrode active materials can be improved to suppress the volume expansion of the negative electrode sheet 121, and the reduction in battery energy density caused by excessive binder content can be reduced.

[0095] It should be noted that, based on 100 parts by weight of the negative electrode film layer 123 , the weight of the binder can be 1 part by weight, 5 parts by weight, 6 parts by weight, 8 parts by weight, or any value within the range of the above values.

[0096] In a possible embodiment, the binder includes at least one of styrene-butadiene and its modifications, styrene-acrylic and its modifications, polyurethane and its modifications, polyvinylidene fluoride and its modifications, and acrylate and its modifications.

[0097] In the embodiment of the present application, by using at least one of styrene butadiene and its modified products, styrene acrylic and its modified products, polyurethane and its modified products, polyvinylidene fluoride and its modified products, and acrylate and its modified products with good bonding strength as a binder, it helps to further improve the bonding strength between the negative electrode active material and the negative electrode current collector 122.

[0098] In one possible embodiment, the silicon-based material includes at least one of a silicon-oxygen material and a silicon-carbon material; optionally, the silicon-oxygen material includes SiO x, wherein 0.4≤x≤1.6; optionally, the silicon-carbon material includes a silicon-carbon composite, and based on the total mass of the silicon-carbon composite, the ratio of the mass content B of the carbon element to the mass content A of the silicon element in the silicon-carbon composite is 1.3≤B / A≤2.

[0099] It should be noted here that silicon-oxygen material refers to a compound composed of silicon and oxygen; silicon-carbon material refers to a compound composed of silicon and carbon.

[0100] In the above scheme, by adding silicon-based materials, especially silicon-oxygen materials or silicon-carbon materials, to the negative electrode active materials, it is beneficial to improve the energy density of the battery. The silicon-oxygen materials in the silicon-based materials not only have high theoretical capacity and excellent stability, but also have the advantages of low cost, non-toxicity and environmental friendliness; silicon-carbon materials have high theoretical capacity and good cycle performance. By using silicon-oxygen materials, especially SiO x , wherein 0.4≤x≤1.6, or using a silicon-carbon material in which the ratio of the mass proportion of silicon element to the silicon-carbon composite A and the mass proportion of carbon element to the silicon-carbon composite B is 1.3≤B / A≤2, can further improve battery performance.

[0101] It should be noted here that, in the silicon-carbon material, the mass ratio B / A of carbon element to silicon element can be 1.3, 1.5, 1.7, 3, and any value within the range of the above values.

[0102] In some embodiments, the negative electrode active material further comprises graphite; wherein, based on 100 parts by weight of the negative electrode film layer 123 , the weight of the graphite is 45 parts by weight to 70 parts by weight, optionally, the weight of the graphite is 55 parts by weight to 65 parts by weight.

[0103] In the above solution, silicon-based materials have high theoretical capacity but poor conductivity. Therefore, if silicon-based materials are used alone as the negative electrode active material, the battery's conductivity will be very poor. By adding graphite, which has high conductivity, to the negative electrode active material and ensuring that the graphite accounts for 45%-70% by weight of the negative electrode film layer 123, particularly 55%-65%, good battery cycle performance can be maintained.

[0104] It should be noted that, based on 100 parts by weight of the negative electrode film 123 , the weight of the graphite can be 50 parts by weight, 58 parts by weight, 65 parts by weight, 72 parts by weight, or any value within the range of the above values.

[0105] In some embodiments, the compaction density of the negative electrode sheet 121 is 1.0 g / cm 3 -2.5g / cm 3 Optionally, the compaction density of the negative electrode sheet 121 is 1.2 g / cm 3-1.8g / cm 3 .

[0106] In the above solution, the compaction density of the negative electrode sheet 121 is set to 1.0 g / cm 3 -2.5g / cm 3 , especially 1.2g / cm 3 -1.8g / cm 3 , which can further improve the energy density of the battery.

[0107] It should be noted that the compaction density of the negative electrode sheet 121 can be 1g / cm 3 , 1.5g / cm 3 , 2.2g / cm 3 , 2.5g / cm 3 and any numerical value within the range consisting of the above numerical values.

[0108] In some embodiments, the thickness d1 of the negative electrode plate 121 is 60 μm-150 μm. Optionally, the thickness d1 of the negative electrode plate 121 is 90 μm-130 μm.

[0109] In the above solution, by setting the thickness d1 of the negative electrode sheet 121 to 60 μm-150 μm, particularly 90 μm-130 μm, the energy density of the battery can be further improved.

[0110] It should be noted that the thickness d1 of the negative electrode sheet 121 can be 60 μm, 80 μm, 100 μm, 120 μm, or any value within the range of the aforementioned values.

[0111] In some embodiments, the negative electrode current collector 122 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 base layer and a metal layer formed on at least one surface of the polymer base layer. 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 base layer (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0112] In some embodiments, the negative electrode active material may also include negative electrode active materials for batteries that are well known in the art. As an example, in addition to silicon-based materials, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based materials, lithium titanate, etc. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. In addition, the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. However, the present application is not limited to these materials, and other traditional 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.

[0113] In some embodiments, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyurethane (PU), nitrile rubber (NBR), polyvinylidene fluoride (PVDF), and styrene acrylic emulsion (SAR).

[0114] In some embodiments, the negative electrode film layer 123 may further 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.

[0115] In some embodiments, the negative electrode film layer 123 may further optionally include other auxiliary agents, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0116] In some embodiments, the negative electrode sheet 121 can be prepared by the following method: the components for preparing the negative electrode sheet 121, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector 122, and after drying, cold pressing and other processes, the negative electrode sheet 121 can be obtained.

[0117] [Positive electrode]

[0118] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0119] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0120] In some embodiments, the positive electrode active material includes Li x (Ni a Co b Mn c ) 1-d M d O2-y A y , wherein M includes at least one of Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, 0.2<x≤1.2, 0.5≤a<1.0, 0≤b<0.5, 0≤c<1, 0≤d<1, and 0≤y<0.02.

[0121] It should be noted that the positive electrode active materials include but are not limited to the following substances: Li 0.5 Ni 0.5 Co 0.1 Mn 0.4 O2、Li 0.5 (Ni 0.5 Co 0.1 Mn 0.4 ) 0.5 Zr 0.5 O 1.9 A 0.1 、LiNi 0.4 Co 0.3 Mn 0.3 O2.

[0122] It should be noted that in the positive electrode sheet, battery, or electrical device, lithium ions are consumed during the battery formation and cycling process, so the measured lithium content in the positive electrode active material may be less than 1. At the same time, if the positive electrode sheet is replenished with lithium, the measured lithium content in the positive electrode active material may be greater than 1 after the battery formation and cycling process.

[0123] Similarly, in the list of positive electrode materials in this application, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0124] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0125] In some embodiments, the positive electrode active material may also adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0126] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0127] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0128] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, and the positive electrode slurry is coated on the positive electrode current collector. After drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0129] [Electrolytes]

[0130] The electrolyte acts as a conductive medium between the positive electrode and the negative electrode 121. The present application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0131] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0132] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0133] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0134] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0135] [Isolation film]

[0136] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0137] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0138] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0139] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0140] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0141] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG2 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0142] Figure 3 is a schematic structural diagram of a battery cell according to an embodiment of the present application. As shown in Figure 3, the outer packaging of the battery cell 100 includes a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet 121 and the isolation film can be formed into an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 100 may be one or more, and those skilled in the art can select according to specific actual needs.

[0143] In some embodiments, the battery cells 100 may be assembled into a battery module. The battery module may contain one or more battery cells 100. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0144] Figure 4 is a schematic diagram of a battery according to one embodiment of the present application, and Figure 5 is a schematic diagram of the structure of a battery according to one embodiment of the present application. Referring to Figures 4 and 5, a battery 400 may include a battery box and a plurality of battery cells 100 disposed within the battery box. The battery box includes an upper box body 401 and a lower box body 402. The upper box body 401 can be placed over the lower box body 402 to form an enclosed space for accommodating the battery cells 100. The plurality of battery cells 100 can be arranged in any manner within the battery box.

[0145] In addition, the present application also provides an electrical device, which includes at least one of the negative electrode plate 121, battery cell 100, or battery 400 provided in the present application. The negative electrode plate 121, battery cell 100, or battery 400 can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0146] For example, FIG6 is a schematic structural diagram of an electric device according to an embodiment of the present application. As shown in FIG6 , the electric device is a vehicle 1. Vehicle 1 may be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor 500, a controller 600 and a battery 400 may be provided inside the vehicle 1. The controller 600 is used to control the battery 400 to supply power to the motor 500. For example, a battery 400 may be provided at the bottom, front or rear of the vehicle 1. The battery 400 may be used to power the vehicle 1. For example, the battery 400 may be used as an operating power source for the vehicle 1, for the circuit system of the vehicle 1, for example, for the working power requirements during the start-up, navigation and operation of the vehicle 1. In another embodiment of the present application, the battery 400 may not only serve as an operating power source for the vehicle 1, but may also serve as a driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0147] As the electrical device, the negative electrode sheet 121 , the battery cell 100 or the battery 400 may be selected according to its usage requirements.

[0148] The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of the battery, a battery cell 100 or a battery 400 may be used.

[0149] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use the battery cell 100 as a power source.

[0150] [Example]

[0151] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0152] [Example 1]

[0153] 1.) Preparation of lithium-ion batteries

[0154] 1.1) Preparation of negative electrode sheet:

[0155] 1.11) Preparation of silicon-carbon materials: This includes providing a gas containing a silicon precursor to carbon-based particles having a carbon skeleton, and generating silicon nanoparticles attached to the carbon skeleton from the silicon precursor through chemical vapor deposition to obtain a carbon-silicon composite material (hereinafter referred to as silicon-carbon material).

[0156] 1.12) Preparation of the binder: A portion of an emulsifier, a portion of an acrylate monomer, and a portion of a styrene monomer are mixed with water to prepare a pre-emulsion; another portion of an emulsifier, another portion of an acrylate monomer, and another portion of a styrene monomer are mixed with water, and an initiator is added to initiate polymerization to prepare a seed emulsion; the pre-emulsion is dropwise added to the seed emulsion, and an initiator is added to initiate polymerization to produce a styrene-acrylic emulsion having a latex sphere Dv50 particle size of 100 nm to 900 nm; wherein the total mass of the emulsifier is 0.7% to 5%, and optionally 1% to 4.5%, of the total mass of the monomers to be prepared; the monomers to be prepared include acrylate monomers and styrene monomers. Based on the total mass of the monomers to be prepared, the styrene-acrylic emulsion comprises, by mass percentage, 30% to 80% of styrene monomer, 20% to 70% of acrylate monomer, and 0% to 10% of functional monomer; the functional monomer methacrylic acid is added during the steps of preparing the pre-emulsion and / or the seed emulsion.

[0157] 1.13) Preparation of negative electrode sheets: A first active material, artificial graphite, a second active material, a silicon-carbon material, a conductive agent, acetylene black, a conductive agent, single-walled CNT, a binder, styrene acrylic emulsion, and a thickener, CMC-Na, are mixed thoroughly in a suitable amount of deionized water solvent system at a weight ratio of 64.4%:30%:1%:0.1%:3.5%:1% to obtain a negative electrode active material. The negative electrode active material is coated on a Cu foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet. The binder, styrene acrylic emulsion, contains a functional group, carboxyl, has a weight of 3.5 parts by weight, a volume average particle size Dv50 of 0.45 μm, a crosslinking degree of 80, a swelling ratio of 25%, a glass transition temperature of 20°C, and an elongation of 100%.

[0158] 1.2) Preparation of positive electrode sheet: The positive electrode active material lithium nickel cobalt manganese oxide (LiNi 0.6 Co 0.2 Mn 0.2 O2), conductive agent carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) are dissolved in a solvent N-methylpyrrolidone (NMP) in a weight ratio of 96%:2%:2%, and the mixture is fully stirred and mixed to obtain a positive electrode active material. The positive electrode active material is coated on an Al foil, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0159] 1.3) Preparation of diaphragm: PE porous polymer film is used as the isolation membrane.

[0160] 1.4) Electrolyte: Dissolve EC / EMC / DMC in 1M LiPF6 at a volume ratio of 1:1:1 and stir evenly.

[0161] 1.5) Assembly: The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide separation. Winding is done to form an electrode assembly, and electrolyte is added. The lithium-ion battery is then hot-pressed at 100°C and 250 MPa for 2 minutes.

[0162] [Example 2]

[0163] The preparation method of the lithium-ion battery of Example 2 is substantially the same as that of Example 1, except that the volume average particle size Dv50 of the binder in the negative electrode sheet in Example 2 is 0.3 μm.

[0164] [Example 3]

[0165] The preparation method of the lithium-ion battery of Example 3 is substantially the same as that of Example 1, except that the volume average particle size Dv50 of the binder in the negative electrode sheet in Example 3 is 0.35 μm.

[0166] [Example 4]

[0167] The preparation method of the lithium-ion battery of Example 4 is substantially the same as that of Example 1, except that the volume average particle size Dv50 of the binder in the negative electrode sheet in Example 4 is 0.5 μm.

[0168] [Example 5]

[0169] The preparation method of the lithium-ion battery of Example 5 is substantially the same as that of Example 1, except that the volume average particle size Dv50 of the binder in the negative electrode sheet in Example 5 is 0.7 μm.

[0170] [Example 6]

[0171] The preparation method of the lithium-ion battery of Example 6 is substantially the same as that of Example 1, except that the crosslinking degree of the binder in the negative electrode plate of Example 6 is 50.

[0172] [Example 7]

[0173] The preparation method of the lithium-ion battery of Example 7 is substantially the same as that of Example 1, except that the crosslinking degree of the binder in the negative electrode plate of Example 7 is 85.

[0174] [Example 8]

[0175] The preparation method of the lithium-ion battery of Example 8 is basically the same as that of Example 1, except that the crosslinking degree of the binder in the negative electrode plate in Example 8 is 98.

[0176] [Example 9]

[0177] The preparation method of the lithium-ion battery of Example 9 is substantially the same as that of Example 1, except that the crosslinking degree of the binder in the negative electrode plate of Example 9 is 100.

[0178] [Example 10]

[0179] The preparation method of the lithium-ion battery of Example 10 is substantially the same as that of Example 1, except that the swelling rate of the binder in the negative electrode sheet in Example 10 is 5%.

[0180] [Example 11]

[0181] The preparation method of the lithium-ion battery of Example 11 is substantially the same as that of Example 1, except that the swelling rate of the binder in the negative electrode plate in Example 11 is 10%.

[0182] [Example 12]

[0183] The preparation method of the lithium-ion battery of Example 12 is substantially the same as that of Example 1, except that the swelling rate of the binder in the negative electrode plate in Example 12 is 50%.

[0184] [Example 13]

[0185] The preparation method of the lithium-ion battery of Example 13 is substantially the same as that of Example 1, except that the swelling rate of the binder in the negative electrode plate in Example 13 is 80%.

[0186] [Example 14]

[0187] The preparation method of the lithium-ion battery of Example 14 is basically the same as that of Example 1, except that the glass transition temperature of the binder in the negative electrode plate in Example 14 is -20°C.

[0188] [Example 15]

[0189] The preparation method of the lithium-ion battery of Example 15 is basically the same as that of Example 1, except that the elongation of the binder in the negative electrode plate in Example 15 is 60°C.

[0190] [Example 16]

[0191] The preparation method of the lithium-ion battery of Example 16 is basically the same as that of Example 1, except that the glass transition temperature of the binder in the negative electrode plate in Example 16 is 200%.

[0192] [Example 17]

[0193] The preparation method of the lithium-ion battery of Example 17 is basically the same as that of Example 1, except that the glass transition temperature of the binder in the negative electrode plate in Example 17 is 50%.

[0194] [Example 18]

[0195] The preparation method of the lithium-ion battery of Example 18 is basically the same as that of Example 1, except that the glass transition temperature of the binder in the negative electrode plate in Example 18 is 400%.

[0196] [Example 19]

[0197] The preparation method of the lithium-ion battery of Example 19 is basically the same as that of Example 1, except that the weight portion of the binder in the negative electrode plate in Example 19 is 1 weight portion, that is, the mass ratio of the first active material artificial graphite and the second active material silicon-carbon material, the conductive agent acetylene black, the conductive agent single-wall CNT, the binder styrene acrylic emulsion (SAR), and the thickener CMC-Na is 66.9%:30%:1%:0.1%:1%:1%.

[0198] [Example 20]

[0199] The preparation method of the lithium-ion battery of Example 20 is basically the same as that of Example 1, except that the weight ratio of the binder in the negative electrode plate in Example 20 is 2 weight parts, that is, the mass ratio of the first active material artificial graphite and the second active material silicon-carbon material, the conductive agent acetylene black, the conductive agent single-wall CNT, the binder styrene acrylic emulsion (SAR), and the thickener CMC-Na is 65.9%:30%:1%:0.1%:2%:1%.

[0200] [Example 21]

[0201] The preparation method of the lithium-ion battery of Example 21 is basically the same as that of Example 1, except that the weight ratio of the binder in the negative electrode plate in Example 21 is 6 weight parts, that is, the mass ratio of the first active material artificial graphite and the second active material silicon-carbon material, the conductive agent acetylene black, the conductive agent single-wall CNT, the binder styrene acrylic emulsion (SAR), and the thickener CMC-Na is 61.9%:30%:1%:0.1%:6%:1%.

[0202] [Example 22]

[0203] The preparation method of the lithium-ion battery of Example 22 is basically the same as that of Example 1, except that the weight ratio of the binder in the negative electrode plate in Example 22 is 8 weight parts, that is, the mass ratio of the first active material artificial graphite and the second active material silicon-carbon material, the conductive agent acetylene black, the conductive agent single-wall CNT, the binder styrene acrylic emulsion (SAR), and the thickener CMC-Na is 59.9%:30%:1%:0.1%:8%:1%.

[0204] [Example 23]

[0205] The preparation method of the lithium-ion battery of Example 23 is basically the same as that of Example 1, except that the binder in the negative electrode plate in Example 23 is polyurethane emulsion.

[0206] [Example 24]

[0207] The preparation method of the lithium-ion battery of Example 24 is basically the same as that of Example 1, except that the binder in the negative electrode plate in Example 24 is nitrile rubber emulsion.

[0208] [Example 25]

[0209] The preparation method of the lithium-ion battery of Example 25 is basically the same as that of Example 1, except that the binder in the negative electrode plate in Example 25 contains hydroxyl groups.

[0210] [Example 26]

[0211] The preparation method of the lithium-ion battery of Example 26 is basically the same as that of Example 1, except that the binder in the negative electrode plate in Example 26 contains amino groups.

[0212] [Example 27]

[0213] The preparation method of the lithium-ion battery of Example 27 is basically the same as that of Example 1, except that the binder in the negative electrode plate in Example 27 contains cyano group.

[0214] [Example 28]

[0215] The preparation method of the lithium-ion battery of Example 28 is basically the same as that of Example 1, except that the volume average particle size Dv50 of the binder in the negative electrode plate in Example 28 is 1 μm.

[0216] [Example 29]

[0217] The preparation method of the lithium-ion battery of Example 29 is basically the same as that of Example 1, except that the volume average particle size Dv50 of the binder in the negative electrode plate in Example 29 is 0.1 μm.

[0218] [Example 30]

[0219] The preparation method of the lithium-ion battery of Example 30 is basically the same as that of Example 1, except that the volume average particle size Dv50 of the binder in the negative electrode plate in Example 30 is 0.8 μm.

[0220] [Comparative Example 1]

[0221] The preparation method of the lithium-ion battery of Comparative Example 1 is substantially the same as that of Example 1, except that no functional group is introduced into the binder in the negative electrode sheet of Comparative Example 1.

[0222] [Comparative Example 2]

[0223] The preparation method of the lithium-ion battery of Comparative Example 2 is substantially the same as that of Example 1, except that the binder in the negative electrode sheet of Comparative Example 2 contains hydroxyl groups.

[0224] [Comparative Example 3]

[0225] The preparation method of the lithium-ion battery of Comparative Example 3 is substantially the same as that of Example 1, except that the volume average particle size Dv50 of the binder in the negative electrode sheet in Comparative Example 3 is 1 μm.

[0226] [Comparative Example 4]

[0227] The preparation method of the lithium-ion battery of Comparative Example 4 is substantially the same as that of Example 1, except that the volume average particle size Dv50 of the binder in the negative electrode sheet in Comparative Example 4 is 5 μm.

[0228] [Comparative Example 5]

[0229] The preparation method of the lithium-ion battery of Comparative Example 5 is substantially the same as that of Example 1, except that the volume average particle size Dv50 of the binder in the negative electrode sheet in Comparative Example 5 is 0.2 μm.

[0230] 2) Performance characterization of lithium-ion battery negative electrode

[0231] 2.1) Measurement of volume average particle size Dv50: Particle size distribution by laser diffraction method according to GB / T 19077-2016 can be measured using a laser particle size analyzer (e.g., Master Size 3000).

[0232] 2.2) Degree of cross-linking: This can be done according to GB / T 36965-2018 or IEC 60811-507-2012.

[0233] 2.3) Swelling rate measurement: Place 20g of sample into a polytetrafluoroethylene petri dish and dry in a 100°C oven to constant weight. Cut the dry film into 20×80mm and weigh the sample W0. Place the dry film into a plastic bottle containing electrolyte and soak at a constant temperature of 60°C. Measure the mass W1, W2, W3, W4, W5, and W6 at intervals of 12h, 24h, 36h, 48h, 60h, and 72h, respectively. Calculate the swelling rate at different time intervals using the following formula: (Wn-W0) / W0×100%.

[0234] 2.4) Measurement of glass transition temperature: According to the standard ISO 11357-2:1999, determination of glass transition temperature, a differential scanning calorimeter can be used for testing.

[0235] 2.5) Measurement of elongation

[0236] 2.51) Film preparation:

[0237] 1. Pretreatment: Pour the sample into a 1L water cup, seal it with plastic wrap, and let it sit for more than 24 hours to eliminate bubbles. 2. Scrape coating: Pour the adhesive into a 280mm×160mm×3mm acrylic tank and apply it by scraping. Let it sit at room temperature for 30 minutes (to eliminate bubbles). 3. Oven drying: Place the sample in a vacuum oven at 60°C (use a spirit level to calibrate the tray in the oven). Bake for 12 hours to form a film. 4. Demolding: After film formation, place the tank in an environment with a humidity of ≤60% for more than 12 hours to dilute it. The film can then be removed.

[0238] 2.52) Film stretching:

[0239] 1. Film sample preparation: Cut the film into strips of 150mm x 20mm;

[0240] 2. Sample selection: Select film strips with uniform thickness (cov < 3.0%) and no bubbles within 50mm in the longitudinal direction;

[0241] 3. Tensile test: Use a tensile testing device to stretch the prepared film at a speed of 10 mm / min until it breaks; calculate the elongation from the stretched displacement;

[0242] 2.6) Measurement of compacted density: Refer to GB / T 24533-2009 for details. Place a certain amount of powder in a compaction mold. Place the mold on a compaction density instrument. Weigh the powder (m) and set the pressure to 400 kN. The instrument reads the thickness (after unloading) and volume (v) of the powder. Calculate the compacted density using the equation ρ = m / v.

[0243] 2.7) Detection of functional groups: can be characterized by infrared spectroscopy, please refer to GB / T 6040-2019 for details.

[0244] Table 1 Specific binder parameters of Examples 1-30 and Comparative Examples 1-5

[0245] 3). Lithium-ion battery performance characterization

[0246] 3.1) Cycling performance test: At 45°C, maintain the battery charge and discharge voltage range between 2.5-4.35V, cycle at a current density of 1C, and record the battery capacity retention rate after 200 cycles. The test results are shown in Table 2.

[0247] 3.2) Test of the bonding strength of the negative electrode sheet: Measure the negative electrode sheet to be tested in the direction perpendicular to the machine direction (TD), cut a sample with a width of 20mm and a length of 100-160mm, and stick a special double-sided tape on the steel plate. The tape is 20mm wide and 90-150mm long. After sticking the cut electrode sample on the double-sided tape, use a 2Kg hand roller to roll it three times in the same direction, and use a tensile tester to test the bonding strength of the electrode sheet. The greater the bonding strength between the negative electrode film layer and the negative electrode current collector in the negative electrode sheet, the stronger the interaction between the active material in the negative electrode film layer and the current collector. Conversely, the weaker the interaction between the active material in the negative electrode film layer and the current collector.

[0248] 3.3) Negative electrode cohesion test: Cut a negative electrode sample with a width of 20mm and a length of 100mm. Attach the sample to double-sided tape, then attach green tape to the sample. The green tape should be 20mm wide and 120mm long. The green tape on the non-contacting electrode should be attached to a 20mm wide and 60mm long piece of paper, with the paper and green tape aligned. The joint between the green tape and the paper should be bonded with wrinkle adhesive. Before testing, the green tape and the contacting electrode should be evenly compacted. The cohesion of the electrode should be tested using a tensile test machine. A greater force between the active particles in the negative electrode film indicates a stronger interaction between the active materials in the negative electrode. Conversely, a weaker force indicates a weaker interaction between the active materials in the electrode.

[0249] Table 2 Performance tests of Examples 1-30 and Comparative Examples 1-5

[0250] In the embodiment of the present application, the bonding force is used to represent the bonding degree between the negative electrode film layer and the negative electrode current collector. The larger the bonding force value, the stronger the interaction force between the negative electrode film layer and the negative electrode current collector, the better the bonding, and the lower the probability of the negative electrode film layer being demolded. The cohesion is used to represent the bonding force between the active materials in the negative electrode film layer. The greater the cohesion, the tighter the connection between the active materials in the negative electrode film layer, and the less likely it is to fall off. The 45°C cycle capacity retention rate is used to represent the cycle performance of the battery. The higher the capacity retention rate value, the better the cycle performance of the battery.

[0251] According to Examples 1-30 and Comparative Examples 1-5, when the binder includes at least one functional group selected from hydroxyl, carboxyl, amino, acrylamide, and cyano, the negative electrode sheet can have both good adhesion and cohesion, thereby improving the cycle performance of the battery.

[0252] According to Examples 1-30 and Comparative Examples 3-5, adding a binder with a volume average particle size Dv50 of 0.1 μm-0.8 μm to the negative electrode film layer can make the negative electrode sheet have better bonding and cohesion, and improve the cycle performance of the battery.

[0253] Furthermore, according to Examples 1-5 and 28-30, adding a binder with a volume average particle size Dv50 of 0.3 μm-0.7 μm, especially a binder with a volume average particle size of 0.35 μm-0.45 μm, to the negative electrode film layer can help further improve the bonding strength, cohesion of the negative electrode sheet and the cycle performance of the battery.

[0254] According to Examples 1, 6-9, adding a binder to the negative electrode film layer and having a cross-linking degree of not less than 50 can give the negative electrode sheet better adhesion and cohesion, thereby reducing demolding and powder loss of the negative electrode sheet and enabling the battery to have better cycle performance; further, maintaining the cross-linking degree of the binder at 80-98 helps to further improve the adhesion and cohesion of the negative electrode sheet and the cycle performance of the battery.

[0255] According to Examples 1, 10-13, by maintaining the swelling rate of the binder added to the negative electrode film layer at 5%-80%, the negative electrode sheet has both good bonding and cohesion, and the cycle performance of the battery is improved; further, by maintaining the swelling rate of the binder at 10%-50%, the bonding and cohesion of the negative electrode sheet and the cycle performance of the battery can be further improved.

[0256] According to Examples 1, 14-15, the glass transition temperature of the binder added to the negative electrode film layer is -20°C-60°C, the negative electrode sheet has good adhesion and cohesion, and the cycle performance of the battery is improved.

[0257] According to Examples 1, 16-18, the elongation of the binder added to the negative electrode film layer is 50%-400%, especially 100%-200%, which can improve the bonding strength and cohesion of the negative electrode sheet and the cycle performance of the battery.

[0258] According to Examples 1 and 19-22, by making the weight portion of the binder in the negative electrode film layer not less than 1 weight portion, especially 2-8 weight portions, the bonding strength and cohesion of the negative electrode sheet, as well as the cycle performance of the battery can be improved.

[0259] It can be seen from Examples 1, 23 and 24 that a variety of adhesives can be applied to the technical solution of this application.

[0260] According to Examples 1 and 25-27, various functional groups are applicable to the technical solutions of this application.

[0261] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode plate, characterized in that: include: A negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector; The negative electrode film layer comprises a negative electrode active material and a binder, wherein the negative electrode active material comprises a silicon-based material; Wherein, the binder includes at least one of the following functional groups: hydroxyl, carboxyl, amino, cyano, lipid, and vinyl.

2. The negative electrode sheet according to claim 1, characterized in that: The volume average particle size Dv50 of the binder is 0.1 μm-0.8 μm.

3. The negative electrode sheet according to claim 1, characterized in that: The volume average particle size Dv50 of the binder is 0.3 μm-0.7 μm.

4. The negative electrode sheet according to claim 1, characterized in that: The volume average particle size Dv50 of the binder is 0.35 μm-0.45 μm.

5. The negative electrode sheet according to claim 1, characterized in that: The volume average particle size Dv50 of the binder is 0.5 μm-0.7 μm.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The crosslinking degree of the binder is 50-100.

7. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The crosslinking degree of the binder is 80-98.

8. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The swelling rate of the binder is 5%-80%.

9. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The swelling rate of the binder is 10%-50%.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that: The glass transition temperature of the binder is -20°C to 60°C.

11. The negative electrode sheet according to any one of claims 1 to 9, characterized in that: The glass transition temperature of the binder is -10°C to 40°C.

12. The negative electrode sheet according to any one of claims 1 to 11, characterized in that: The elongation of the adhesive is 50%-400%.

13. The negative electrode sheet according to any one of claims 1 to 11, characterized in that: The elongation of the adhesive is 100%-200%.

14. The negative electrode sheet according to any one of claims 1 to 13, characterized in that: Based on 100 parts by weight of the negative electrode film layer, the weight part of the binder is 1 part by weight to 10 parts by weight.

15. The negative electrode sheet according to any one of claims 1 to 14, characterized in that: The binder comprises at least one of styrene-butadiene and its modified products, styrene-acrylic and its modified products, polyurethane and its modified products, polyvinylidene fluoride and its modified products, and acrylate and its modified products.

16. The negative electrode sheet according to any one of claims 1 to 15, characterized in that: The silicon-based material includes at least one of a silicon-oxygen material and a silicon-carbon material.

17. The negative electrode sheet according to any one of claims 1 to 16, characterized in that: The negative electrode active material also includes graphite; Wherein, based on 100 parts by weight of the negative electrode film layer, the weight of the graphite is 45 parts by weight to 70 parts by weight.

18. The negative electrode sheet according to any one of claims 1 to 17, characterized in that: The compaction density of the negative electrode plate is 1.0 g / cm 3 -2.5g / cm 3 .

19. The negative electrode sheet according to any one of claims 1 to 18, characterized in that: The thickness of the negative electrode plate is 60 μm-150 μm.

20. A battery cell, characterized in that: A negative electrode sheet comprising the negative electrode sheet according to any one of claims 1 to 19.

21. The battery cell according to claim 20, characterized in that: The battery cell further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material.

22. The battery cell according to claim 21, characterized in that: The positive electrode active material includes Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y , wherein M includes at least one of Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, 0.2<x≤1.2, 0.5≤a<1.0, 0≤b<0.5, 0≤c<1, 0≤d<1, and 0≤y<0.

02.

23. A battery, characterized in that: Comprising the battery cell according to any one of claims 20 to 22.

24. An electrical device, characterized in that: Comprising a battery as claimed in claim 23.

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