Safety coating and use thereof, electrode sheet and lithium-ion battery

Abstract

The present invention relates to the technical field of secondary battery materials. Disclosed are a safety coating and the use thereof, an electrode sheet and a lithium-ion battery. By limiting the particle size of an inorganic filler in the safety coating, particle size grading is achieved, which enables the safety coating to have a compact structure, thereby reducing the probability of contact between positive and negative electrodes and thus improving the safety performance of a battery cell. Moreover, the amount of the binder in the safety coating is optimized to promote the electrolyte absorption of the safety coating, which can improve the rate capability, the low-temperature discharge performance and the cycle performance of a battery cell. Ultimately, in the present invention, by limiting the particle size of the inorganic filler and selecting the binder, the rate capability, low-temperature discharge performance and cycle performance of a battery cell can be improved while the safety performance of the battery cell is enhanced.

Description

A safety coating and its application, electrode sheet and lithium-ion battery Technical Field

[0001] This invention relates to the field of secondary battery materials technology, and in particular to a safety coating and its application, electrode sheets, and lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used in products such as 3C products, electric vehicles, and power tools due to their advantages such as high energy density, no memory effect, long cycle life, environmental friendliness, and adaptability to various environments.

[0003] In practical applications, the requirements for the safety and cycle performance of lithium batteries are becoming increasingly stringent. To improve battery safety, introducing safety coatings into the battery electrodes is a common industry practice. These coatings typically contain a certain proportion of inorganic fillers, conductive agents, and binders. However, conventional safety coating structures are relatively porous, failing to effectively improve cell safety and increasing internal resistance, leading to increased cell polarization and deterioration in low-temperature performance, rate performance, and cycle performance. Furthermore, lithium-ion batteries are prone to lithium plating due to kinetic limitations, resulting in reduced cycle and rate performance. When lithium plating occurs, increased side reactions lead to electrolyte consumption, and the formation of a new solid electrolyte interphase (SEI) during cycling further depletes the electrolyte, accelerating cycle performance degradation. In addition, during mechanical abuse tests such as nail penetration, short circuits and thermal runaway may occur at the positive and negative electrodes, leading to test failure.

[0004] Therefore, it is of great significance to solve the problem that current safety coatings cannot effectively improve the rate performance and cycle performance of battery cells, and to provide a safety coating that can improve the rate performance, low-temperature discharge performance and cycle performance of battery cells while improving their safety performance. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a safety coating and its application, electrode sheets, and a lithium-ion battery, aiming to address the problem that current safety coatings cannot effectively improve the low-temperature performance, rate performance, and cycle performance of the battery cell.

[0006] In a first aspect, the present invention provides a safety coating, the raw materials of which include an inorganic filler and a first binder; the non-uniformity coefficient C of the inorganic filler is... u Satisfying 2≤C u ≤18, curvature coefficient C c Satisfying 0.5≤C c ≤3.1; The mass fraction w of the first adhesive in the safety coating satisfies w=k×(C u )0.5 / D v50 And 0.2≤k≤2, where k is a constant;

[0007] Wherein, the non-uniformity coefficient C u The calculation formula is: C u =D v90 / D v10 The curvature coefficient C c The calculation formula is: C c =D v50 ×D v50 / (D v10 ×D v90 );

[0008] D v10 D v50 D v90 These represent the particle sizes corresponding to the cumulative volume distribution of inorganic fillers reaching 10%, 50%, and 90%, respectively.

[0009] The safety coating according to embodiments of the present invention has at least the following beneficial effects: The safety coating provided by the present invention comprises inorganic fillers and binders. By limiting the particle size of the inorganic fillers and selecting the binder, the rate performance, low-temperature discharge performance, and cycle performance of the battery cell can be improved while enhancing the safety performance of the battery cell. Specifically, the particle size D of the inorganic fillers... v10 D v50 D v90 It should satisfy 2≤Cu=D v90 / D v10 ≤18, 0.5≤C c =D v50 ×D v50 / (D v10 ×D v90 )≤3.1, C u and C c These are the non-uniformity coefficient and curvature coefficient of the inorganic packing, respectively, D. v10 D v50 D v90 These represent the particle sizes corresponding to cumulative volume distribution values ​​of inorganic fillers reaching 10%, 50%, and 90%, respectively. When the particle size of the inorganic filler satisfies the above relationship, its gradation curve exhibits good continuity, with a good gradation of fine and coarse particles. This allows the safety coating to have a relatively dense structure, thereby reducing the probability of short circuits between the positive and negative electrodes and improving the safety performance of the battery cell. The mass fraction w of the first binder should satisfy w = k × (C u ) 0.5 / D v50When k is within the range of 0.2 ≤ k ≤ 2, the binder not only provides sufficient adhesion and reduces cell polarization, but also promotes the absorption of electrolyte by the safety coating, improving the cell's rate performance, low-temperature discharge performance, and cycle performance. Ultimately, the safety coating provided by this invention, by limiting the particle size of the inorganic filler, achieves a particle size distribution, resulting in a denser structure that reduces the probability of positive and negative electrode contact, thereby improving the cell's safety performance. Simultaneously, optimizing the amount of binder in the safety coating promotes electrolyte absorption, further enhancing the cell's rate performance, low-temperature discharge performance, and cycle performance.

[0010] In this invention, the non-uniformity coefficient C of the inorganic filler particle size is... u =D v90 / D v10 It should satisfy: 2≤C u =D v90 / D v10 ≤18. Coefficient of non-uniformity (C) u C is an important parameter describing the particle size distribution of inorganic fillers, reflecting the degree of non-uniformity in particle size. u When C is greater than 18, it indicates that the particle size distribution of the inorganic filler is wide, with some particles having particularly large sizes. This may lead to missed areas during the application of the safety coating, thus adversely affecting the safety performance of the battery cell. u When the value is less than 2, the particle size distribution range of the inorganic filler is narrow, with most particles having similar sizes. There are not enough fine particles to fill the gaps between larger particles, resulting in poor gradation. At this point, the density of the safety coating is low, negatively impacting the safety performance and energy density of the battery cell. When the value is within the above range, the safety coating can have a denser structure, and it is less prone to missed areas during application, resulting in superior overall performance.

[0011] In this invention, the curvature coefficient C of the inorganic filler c =D v50 ×D v50 / (D v10 ×D v90 It should satisfy: 0.5≤C c =D v50 ×D v50 / (D v10 ×D v90 )≤3.1. Curvature coefficient (C) c ) is a parameter describing the shape of the particle size distribution curve. When C cWhen the value of C is 1, the particle size distribution of the inorganic filler is ideal; the particle size distribution is continuous, without obvious particle size jumps or gaps, and the shape of the particle size distribution curve is uniform, meaning the transition from fine to coarse particles is smooth. When C... c When C is not equal to 1, it indicates that the particle size distribution of the inorganic filler deviates from the ideal state. c When C is greater than 1, it indicates that the particle size distribution curve is convex on the logarithmic particle size diagram, meaning that the particle size distribution in the fine particle portion is more concentrated than that in the coarse particle portion. Conversely, when C... c When the value is less than 1, it indicates that the particle size distribution curve is concave, meaning that the particle size distribution of the coarse particles is more concentrated than that of the fine particles. However, the particle size distribution of inorganic fillers often deviates from the ideal state. The vast majority of inorganic fillers are fine or coarse particles, resulting in a discontinuous overall shape of the gradation curve, leading to higher porosity and lower density of the safety coating. This invention uses C... c The range of values ​​is limited to the above values, which can ensure good continuity of the gradation curve, thereby helping to improve the density of the safety coating.

[0012] In this invention, the amount w of the first adhesive should satisfy w = k × (C u ) 0.5 / D v50 0.2≤k≤2, where k is a constant related to the density of the inorganic filler. Generally, given a fixed particle shape and pore structure, the D of the particles... v50 The smaller the value, the larger its specific surface area, and the larger the contact area with the adhesive. Consequently, the amount of adhesive needed needs to be increased. u This indicates the distribution of particles, C u A smaller value means that all particle sizes tend to be D. v50 A smaller number of fine particles in the system results in a smaller overall specific surface area, thus reducing the amount of binder required. The k value indicates the level of binder usage in the safety coating. When k < 0.2, the adhesion between the safety coating and the current collector is poor, posing a risk of detachment. When k > 2, it leads to increased cell polarization, resulting in deterioration of the cell's rate performance, low-temperature discharge performance, and cycle performance. When k is in the range of 0.2 to 2, not only is the adhesion sufficient and the cell polarization low, but it also promotes the absorption of electrolyte by the safety coating, improving the cell's rate performance, low-temperature discharge performance, and cycle performance.

[0013] In some embodiments of the present invention, the median particle size D of the inorganic filler is... v50 The range is 0.2–4 μm, and the specific surface area is 5–50 m². 2 / g. When the D of inorganic filler v50 Smaller than 0.2 μm, but with a specific surface area greater than 50 m². 2When the density of inorganic packing is / g, it is prone to agglomeration and difficult to disperse; when the density of inorganic packing is / g, it is prone to agglomeration and difficult to disperse. v50 Greater than 4μm, while specific surface area is less than 5m². 2 At a particle size of / g, the relatively large particle size makes it difficult to obtain a thin safety coating, thus affecting the energy density of the battery cell. Furthermore, undercoating is prone to occur during safety coating application, compromising battery cell safety. When the median particle size and specific surface area of ​​the inorganic filler are within the aforementioned range, a better balance can be achieved between the processability of the safety coating and the energy density of the battery cell.

[0014] In some embodiments of the present invention, the inorganic filler includes one or more of alumina, boehmite, aluminum hydroxide, magnesium hydroxide, silicon dioxide, titanium dioxide, lithium iron phosphate, lithium manganese iron phosphate, lithium titanium aluminum phosphate, lithium lanthanum titanate, or lithium lanthanum zirconium oxide, preferably boehmite. The inorganic filler used in the present invention can be inert inorganic fillers such as alumina, boehmite, aluminum hydroxide, magnesium hydroxide, silicon dioxide, and titanium dioxide; it can also be active materials with good thermal stability and a certain capacity, such as lithium iron phosphate and lithium manganese iron phosphate; or it can be solid electrolytes such as lithium titanium aluminum phosphate (LATP), lithium lanthanum titanate (LLTO), and lithium lanthanum zirconium oxide (LLZO). Boehmite is preferred because, compared to other inorganic fillers, boehmite is not only cheaper but also has a lower Rockwell hardness, resulting in less wear on the gravure roller, thereby reducing manufacturing costs.

[0015] In some embodiments of the present invention, the mass fraction of inorganic filler in the safety coating is 73.8% to 98.5%.

[0016] In some embodiments of the present invention, the first adhesive includes one or more of polyvinylidene fluoride (PVDF) adhesive, sodium carboxymethyl cellulose (CMC) adhesive, or polyacrylate (PAA) adhesive.

[0017] In some embodiments of the present invention, the mass fraction of the first binder in the safety coating is 1 wt% to 21.2 wt%, preferably 5 wt% to 15 wt%. When the amount of binder in the safety coating is less than 1%, the adhesion of the safety coating is insufficient, and it is prone to peeling off during later use; when the amount of binder is greater than 21.2%, it will cause difficulties in processing the safety coating during gravure printing, and will also worsen the internal resistance of the battery cell. In addition, the amount of binder is 1% to 21.2%, which can also adjust the pH of the paste to below 8.5, thereby reducing the corrosion of the current collector aluminum foil by the aqueous solution of the alkaline active material.

[0018] In some preferred embodiments of the present invention, the first adhesive is a polyacrylate adhesive, which can reduce the corrosion of aluminum foil by active substances, has good bonding performance, and is inexpensive. The solvent is deionized water, which is environmentally friendly.

[0019] In some embodiments of the present invention, the structural formula of the polyacrylate adhesive is as follows:

[0020] Each time R1 appears, it is independently selected from H, Li, or Na;

[0021] Each occurrence of R2 is independently selected from substituted or unsubstituted C1 to C2. 10 Alkyl groups;

[0022] And 5≤(x+z) / y≤20, 1.2≤z / x≤2, and x, y, and z are all not 0.

[0023] The polyacrylate binder provided by this invention achieves excellent bonding performance by limiting the content of cyano (-CN), ester (-COOR2), and carboxylate (-COOR1) groups in the binder molecular chain. Furthermore, the binder is water-soluble, using water as the solvent, eliminating the need for harmful organic solvents such as NMP, making it harmless to humans and environmentally friendly. It is also abundant and inexpensive, allowing for widespread application in industrial production. Introducing this binder as a raw material for an aqueous safety coating onto the electrode sheet, its excellent bonding properties enable the aqueous safety coating to adhere firmly to the current collector surface of the electrode sheet. This not only reduces surface contact resistance but also minimizes the formation of current collector burrs during cell safety testing, reducing short circuits between current collector burrs and unstable active materials in the charged state, thereby improving cell safety. Moreover, by limiting the molecular weight of the binder and the content of cyano, ester, and carboxylate groups in the molecular chain, the electrolyte absorption rate of the binder can be adjusted, significantly improving the rate performance and high / low temperature discharge performance of the cell, and enhancing battery safety and cycle performance.

[0024] The adhesive provided by this invention comprises a cyano group (-CN, the proportion of which in the total side chain groups is n1, n1 = z / (x+y+z)), a carboxylate group (-COOR1, R1 is independently selected from H, Li, and Na each time it appears, the proportion of which in the total side chain groups is n2, n2 = x / (x+y+z)) and an ester group (-COOR2, R2 is independently selected from substituted or unsubstituted C1 to C2 each time it appears). 10 The alkyl group has an alkyl group that accounts for n3% of all side chain groups, where n3 = y / (x+y+z)) and n1+n2+n3 = 1.

[0025] Among them, -CN is a strongly polar group with good electrolyte affinity and electrochemical stability, and can provide greater adhesion. However, this group is relatively rigid and cannot cope with the huge volume changes that occur when lithium ions are inserted into / extracted from the active material.

[0026] Among them, -COOR1 carries a negative charge and repels each other, which helps the adhesive molecules to stretch and promotes the uniform dispersion of the conductive agent. At the same time, it can also regulate the swelling degree of the adhesive in the electrolyte solvent, reduce the erosion of the adhesive by the electrolyte, and better maintain the adhesion and bonding effect.

[0027] Among them, -COOR2 has polarity and solubility parameters close to those of carbonate solvents in the electrolyte, which is conducive to the binder absorbing the electrolyte appropriately. The absorption of the electrolyte will plasticize the binder, making it elastic and flexible to adapt to the periodic volume changes of the electrode active material during charging and discharging as lithium ions are inserted and extracted. At the same time, the absorption of the electrolyte will also improve the ionic conductivity of the water-based safety coating and promote the improvement of the low-temperature discharge performance of the battery cell.

[0028] Binders are essential for maintaining electrode integrity and are crucial for improving battery performance, including specific capacity and cycle stability. Polyacrylic acid (PAA) is used as a binder for both positive and negative electrodes in lithium-ion batteries due to its numerous polar functional groups, water solubility, and good adhesion. However, the polar groups in PAA result in high chain rigidity due to hydrogen bonds formed between molecular chains, which is detrimental to maintaining electrode integrity during charge and discharge. Therefore, controlling the number and type of PAA functional groups and modifying the PAA molecular chain structure are essential for improving the electrical performance of lithium-ion batteries. This invention limits the content of cyano groups, ester groups, and carboxylate groups in the adhesive molecular chain: (1) Limiting 1.2≤z / x≤2, that is, n1 and n2 satisfy 1.2≤n1 / n2≤2; when n1 / n2<1.2, it is easy to cause insufficient adhesive force; while when n1 / n2>2, the molecular chain is in a coiled state, which is not conducive to the dispersion of conductive agent, and the adhesive is more susceptible to the effect of electrolyte swelling; (2) Limiting 5≤(x+z) / y≤20, that is, n1, n2, and n3 satisfy 5 The values ​​of -COOR2 and (n1+n2) / n3 are ≤20. When (n1+n2) / n3 < 5, the binder contains excessive -COOR2, which easily absorbs excessive electrolyte, causing a rapid decrease in adhesion, poor elasticity, and deterioration of cell performance. Conversely, when (n1+n2) / n3 > 20, the -COOR2 content in the binder is too low, resulting in insufficient elasticity, low ionic conductivity of the water-based safety coating, and a significant reduction in the cell's low-temperature and high-rate discharge performance. Ultimately, this invention achieves good adhesion of the binder and regulates the electrolyte absorption rate of the binder by controlling the content of cyano, ester, and carboxyl groups in the binder molecular chain, thereby improving the cell's rate and high / low temperature discharge performance.

[0029] In some embodiments of the present invention, each occurrence of R2 is independently selected from C1 to C2. 10 Straight-chain alkyl, branched alkyl, or cycloalkyl groups, preferably C1 to C2. 10The straight-chain alkyl group, more preferably a C1 to C4 alkyl group.

[0030] In some embodiments of the present invention, the electrolyte absorption rate c of the polyacrylate adhesive at 80°C is 10% to 50%, for example, it can be 10% to 20%, 20% to 30%, 30% to 40%, or 40% to 50%.

[0031] This invention achieves regulation of the electrolyte absorption rate of the binder by limiting the content of cyano, ester, and carboxyl groups in the binder molecular chain. The electrolyte absorption rate c of the binder at 80°C satisfies 10% ≤ c ≤ 50%. When c < 10%, the binder absorbs insufficient electrolyte, has poor elasticity, and cannot buffer the periodic volume changes caused by lithium ion insertion / extraction from the active material. Furthermore, the ionic conductivity of the water-based safety coating is low, leading to deterioration in the low-temperature discharge performance and rate discharge performance of the battery cell. When c > 50%, the binder absorbs excessive electrolyte, causing the water-based safety coating to expand, reducing adhesion, increasing internal resistance, and similarly leading to deterioration in battery cell performance.

[0032] In some embodiments of the present invention, the weight-average molecular weight M of the polyacrylate adhesive is... w The range is 200,000 to 500,000, for example, it can be 200,000, 250,000, 300,000, 350,000, 400,000, 450,000, or 500,000.

[0033] In some embodiments of the present invention, the number-average molecular weight M of the polyacrylate adhesive is... n The range is 100,000 to 400,000, for example, it can be 100,000, 150,000, 200,000, 250,000, 300,000, 350,000, or 400,000.

[0034] In some embodiments of the present invention, the weight-average molecular weight M of the polyacrylate adhesive is... w Number-average molecular weight M n The proportion satisfies M w / M n ≤3, preferred M w / M n The range is 1.5 to 1.9.

[0035] If the molecular weight of the adhesive is too low, not only will the bonding strength be too low, but the amount of adhesive required will also increase; if the molecular weight is too high, the viscosity will be too high, making processing difficult. M... w / M n >3 indicates that the molecular weight distribution of the binder is too dispersed, which deteriorates the performance of the water-based safety coating.

[0036] In some embodiments of the present invention, the mass fraction of the polyacrylate binder in the safety coating is 1 wt% to 21.2 wt%, preferably 5 wt% to 15 wt%. When the amount of binder in the safety coating is less than 1%, the adhesion of the safety coating is insufficient, and it is prone to peeling off during later use; when the amount of binder is greater than 21.2%, it will cause difficulties in processing the safety coating during gravure printing, and will also worsen the internal resistance of the battery cell. In addition, the amount of binder is 1% to 21.2%, which can also adjust the pH of the paste to below 8.5, thereby reducing the corrosion of the current collector aluminum foil by the alkaline aqueous solution of the active material.

[0037] The above-mentioned polyacrylate adhesives can be prepared using conventional methods in the art, such as emulsion polymerization, solution polymerization, bulk polymerization, and suspension polymerization.

[0038] In one specific embodiment, the present invention also provides a method for preparing the above-mentioned polyacrylate adhesive, comprising the steps of:

[0039] S1. Add dispersion medium to the reaction vessel and remove oxygen;

[0040] S2. According to the ratio of x, y, z, add a certain amount of acrylonitrile, monomer A providing -COOR1, and monomer B providing -COOR2 into the reaction vessel;

[0041] S3. Add an initiator and heat to initiate the reaction;

[0042] S4. After the reaction is complete, the product is filtered, dried, crushed and sieved to obtain a polyacrylate adhesive.

[0043] In some embodiments of the present invention, monomer A includes at least one of acrylic acid, lithium acrylate, and sodium acrylate, but is not limited thereto. The purpose of adding monomer A is to provide -COOR1, where R1 is selected from H, Li, or Na. Those skilled in the art can choose a suitable monomer A as needed, and all such modifications should be considered reasonable variations within the scope of the present invention.

[0044] In some embodiments of the present invention, monomer B includes at least one of methyl acrylate, ethyl acrylate, and butyl acrylate, but is not limited thereto, and may also be C1 to C2. 10 At least one of the acrylates. The purpose of adding monomer B is to provide -COOR2, where R2 is selected from substituted or unsubstituted C1 to C2. 10 The alkyl group, and those skilled in the art can choose a suitable monomer B as needed, all of which should be considered reasonable modifications within the scope of this invention.

[0045] In some embodiments of the present invention, in step S1, distilled water is added to the reaction vessel, stirring is started, and high-purity nitrogen gas is introduced to remove oxygen.

[0046] In some embodiments of the present invention, in step S2, after adding acrylonitrile, monomer A providing -COOR1, and monomer B providing -COOR2, the mixture is heated to 65°C under an inert atmosphere and kept at that temperature.

[0047] In some embodiments of the present invention, the initiator includes 20% ammonium persulfate, but is not limited thereto.

[0048] In some embodiments of the present invention, the raw material of the safety coating further includes a first conductive agent. The safety coating satisfies at least one of the following:

[0049] A1) The mass fraction of the first conductive agent in the safety coating is 0.5% to 5%;

[0050] A2) The mass ratio of the first conductive agent, the first binder, and the inorganic filler is (0.5~5):(1~21.2):(73.8~98.5);

[0051] A3) The raw materials for the safety coating also include heat-stabilized active substances;

[0052] A4) When A3) is included, the mass ratio of the first conductive agent, the first binder, the inorganic filler, and the thermally stable active substance is (0.5~5):(1~21.2):(1~97.5):(1~97.5);

[0053] A5) When A3) is included, the thermally stable active material includes one or both of lithium iron phosphate and lithium manganese iron phosphate.

[0054] In some embodiments of the present invention, the mass fraction of the first conductive agent in the safety coating is 0.5% to 5%, preferably 1% to 3.5%. Too low a conductive agent content will result in high resistance of the water-based safety coating film and poor cell cycle performance; too high a content will result in low resistance of the water-based safety coating film and poor cell safety. When the conductive agent content is between 0.5 wt% and 5 wt%, both safety and cycle performance can be balanced.

[0055] In some embodiments of the present invention, the first conductive agent includes at least one selected from acetylene black, graphene, graphylene, carbon nanotubes, carbon fibers, and conductive carbon black. The present invention does not have special requirements for the first conductive agent; conventional conductive agents in the art can be used, such as conductive carbon black or carbon nanotubes, and more specifically, super-dense high-conductivity carbon black SUPER P Li.

[0056] In some embodiments of the present invention, the mass ratio of the first conductive agent, the first binder, and the inorganic filler is (0.5–5):(1–21.2):(73.8–98.5). For example, by weight, the first conductive agent can be 0.5–5 parts, preferably 1.5–3 parts; the first binder can be 1–21.2 parts, preferably 5–15 parts; and the inorganic filler can be 73.8–98.5 parts.

[0057] In some embodiments of the present invention, the raw materials of the safety coating further include thermally stable active substances.

[0058] In some embodiments of the present invention, the mass ratio of the first conductive agent, the first binder, the inorganic filler, and the thermally stable active substance is (0.5-5):(1-21.2):(1-97.5):(1-97.5).

[0059] In some embodiments of the present invention, the raw materials of the safety coating include a first binder, a first conductive agent, an inorganic filler, and a heat-stabilizing active substance, wherein the mass ratio satisfies: first conductive agent: first binder: inorganic filler: heat-stabilizing active substance = (0.5-5):(1-21.2):(1-97.5):(1-97.5). For example, by weight, the first conductive agent can be 0.5-5 parts, the first binder can be 1-21.2 parts, the inorganic filler can be 1-97.5 parts, and the heat-stabilizing active substance can be 1-97.5 parts.

[0060] In some embodiments of the present invention, the thermally stable active material includes one or both of lithium iron phosphate and lithium manganese iron phosphate.

[0061] In a second aspect, the present invention provides an electrode sheet comprising: a current collector, an active material layer, and the aforementioned safety coating.

[0062] The electrode sheet according to embodiments of the present invention has at least the following beneficial effects: The present invention provides an electrode sheet comprising a safety coating. The safety coating comprises a binder and the aforementioned inorganic filler and conductive agent. By limiting the particle size of the inorganic filler and selecting the binder content, the rate performance, low-temperature discharge performance, and cycle performance of the battery cell can be improved while simultaneously enhancing the cell's safety performance. Introducing the aforementioned safety coating into the electrode sheet not only improves the battery's safety performance but also significantly enhances its rate performance, low-temperature discharge performance, and cycle performance.

[0063] In some embodiments of the present invention, the safety coating is applied to at least one side of the current collector, and the active material layer is applied to the side of the safety coating away from the current collector and / or to the side of the current collector away from the water-based safety coating.

[0064] Specifically, the electrode sheet is a positive electrode sheet, the safety coating is coated on at least one side of the current collector, and the active material layer is coated on the side of the safety coating away from the current collector and / or on the side of the current collector away from the water-based safety coating.

[0065] More specifically, the electrode sheet is a positive electrode sheet, the safety coating is coated on both sides of the current collector, and the active material layer is coated on the surface of the safety coating away from the current collector.

[0066] In other embodiments of the invention, the active material layer is coated on at least one side of the current collector, and the safety coating is coated on the side of the active material layer away from the current collector and / or on the side of the current collector away from the active material layer.

[0067] Specifically, the electrode sheet is a negative electrode sheet, the active material layer is coated on at least one side of the current collector, and the safety coating is coated on the side of the active material layer away from the current collector and / or on the side of the current collector away from the active material layer.

[0068] More specifically, the electrode sheet is a negative electrode sheet, the active material layer is coated on both sides of the current collector, and the safety coating is coated on the surface of the active material layer away from the current collector.

[0069] The electrode sheet provided by this invention can be used as a positive electrode sheet or a negative electrode sheet, preferably a positive electrode sheet. When used as a positive electrode sheet, the safety coating is closer to the current collector, and its structure is "current collector-safety coating-active material layer", as shown in Figure 1. The positive electrode sheet 01 includes the following structure: a current collector 022; a safety coating 023 disposed on at least one surface of the current collector 022; and an active material layer 011 disposed on the surface of the safety coating 023 away from the current collector 022. When used as a negative electrode sheet, the active material layer is closer to the current collector, and its structure is "current collector-active material layer-safety coating".

[0070] Internal short circuits in lithium-ion batteries can generally be categorized into several types: 1) short circuits between the positive and negative electrode current collectors; 2) short circuits between the positive and negative electrode active materials; 3) short circuits between the negative electrode active material and the positive electrode current collector; and 4) short circuits between the positive electrode active material and the negative electrode current collector. Among these, the short circuit between the negative electrode active material and the positive electrode current collector has the lowest impedance and the lowest trigger temperature for the exothermic reaction at the negative electrode. Therefore, the short circuit between the negative electrode active material and the Al foil is the most dangerous. This invention introduces a safety coating with high adhesion to the surface of the positive electrode current collector, reducing the probability of contact between the positive electrode current collector and the negative electrode active material, thereby effectively improving the safety performance of the battery cell.

[0071] In some embodiments of the present invention, the thickness of the safety coating is 1 to 20 μm, for example, it can be 1 to 7 μm, 7 to 14 μm, or 14 to 20 μm.

[0072] In some embodiments of the present invention, the surface density of the safety coating is 2–35 mg / 1540.25 mm. 2 For example, it can be 2-8 mg / 1540.25 mm. 2 8-15mg / 1540.25mm 2 14-21 mg / 1540.25 mm 2 20-28mg / 1540.25mm 2 28-35mg / 1540.25mm 2 .

[0073] There is a positive correlation between the coating density and thickness of the safety coating. If the thickness is too low, the safety performance of the battery cell will be poor; if the thickness is too high, it will reduce the energy density of the battery cell.

[0074] In some embodiments of the present invention, the diaphragm resistance of the safety coating at a pressure of 0.4t is 0.5–5Ω, for example, 0.5–2Ω, 2–3.5Ω, or 3.5–5Ω. The diaphragm resistance of the safety coating is a primary factor affecting the safety performance of the battery cell. If this value is too low, the safety performance of the battery cell will deteriorate, while if it is too high, the cycle performance of the battery cell will worsen. A value between 0.5–5Ω@0.4T can balance both safety performance and cycle performance.

[0075] In some embodiments of the present invention, the adhesion strength between the safety coating and the current collector is not less than 100 N / m. If the adhesion strength is less than 100 N / m, the water-based safety coating is at risk of detachment during subsequent use.

[0076] In some embodiments of the present invention, the raw materials of the active material layer include an active material, a second conductive agent, and a second binder.

[0077] In some embodiments of the present invention, the active substance accounts for 90% to 98% of the mass percentage of the active substance layer.

[0078] In some embodiments of the present invention, the second conductive agent accounts for 0.5% to 5% of the mass percentage of the active material layer, preferably 0.5% to 2%. If the content of the second conductive agent is too low, the cycle performance of the battery cell will be poor; if the content is too high, it will be beneficial to improve the cycle performance, but it will lead to poor battery cell safety performance.

[0079] In some embodiments of the present invention, the second conductive agent includes at least one selected from acetylene black, graphene, graphylene, carbon nanotubes, carbon fibers, and conductive carbon black. The present invention does not have special requirements for the second conductive agent; conventional conductive agents in the art can be used, such as conductive carbon black or carbon nanotubes, and more specifically, ultra-dense high-conductivity carbon black SUPER P Li.

[0080] In some embodiments of the present invention, the second adhesive accounts for 0.5% to 5% of the mass percentage of the active material layer. If the amount of the second adhesive is too small, the adhesion of the active material layer will be insufficient, and it will easily fall off during later use; if the amount of the second adhesive is too large, it will make the active material layer difficult to process and will also worsen the internal resistance of the cell.

[0081] In some embodiments of the present invention, the second adhesive includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and PAA-type adhesives. The present invention does not have special requirements for the second adhesive; conventional adhesives in the art can be used.

[0082] In one specific embodiment, the active material layer may be a positive electrode active material layer, and the raw materials of the positive electrode active material layer include a positive electrode active material, a second conductive agent, and a second binder.

[0083] The positive electrode active material is not limited and can be one or more of common lithium cobalt oxide, lithium iron phosphate, and ternary materials, with an amount of 90wt% to 98wt% of the total weight of the active material layer. While ensuring that the active material has a certain conductivity and binding force, the higher the content of the active material, the better, thereby giving the battery cell a higher energy density.

[0084] The second binder is not limited and can be a common cathode binder, including polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), and PAA-type binders, with a dosage of 0.5 wt% to 5 wt% of the total weight of the active material layer. If the amount of the second binder is too small, the adhesion of the active material layer will be insufficient, making it prone to detachment during later use; if the amount of the second binder is too large, it will make the active material layer difficult to process and will also worsen the internal resistance of the cell. Considering that it does not directly contact the current collector, its upper limit can be appropriately reduced to ensure that the positive electrode active material does not detach during cell use. At the same time, a lower dosage can also improve the cycle performance of the cell, increase the amount of positive electrode active material, and improve the energy density of the cell.

[0085] In one specific embodiment, the active material layer may be a negative electrode active material layer, and the raw materials of the negative electrode active material layer include a negative electrode active material, a second conductive agent, and a second binder.

[0086] The negative electrode active material is not limited and can be one or more of the common artificial graphite, natural graphite, modified graphite, silicon oxide compounds, silicon-carbon composites and other silicon negative electrode materials, and the amount used is 90wt% to 98wt% of the total weight of the active material layer.

[0087] In some embodiments of the present invention, the electrode sheet further includes a current collector. The current collector is not limited and can be any common current collector. For example, when the electrode sheet is a positive electrode sheet, the current collector can be aluminum foil or composite aluminum foil; when the electrode sheet is a negative electrode sheet, the current collector can be copper foil or composite copper foil.

[0088] In some preferred embodiments of the present invention, the dyne value of the current collector is ≥30 dyn / cm, preferably ≥38 dyn / cm.

[0089] In some embodiments of the present invention, the safety coating is applied to both sides of the current collector.

[0090] The safety coating satisfies at least one of the following:

[0091] B1) The thickness of the safety coating on both sides is 1–20 μm;

[0092] B2) The double-sided coating surface density of the safety coating is 2–35 mg / 1540.25 mm². 2 ;

[0093] B3) The double-sided diaphragm resistance of the safety coating tested under 0.4t pressure is 0.5~5Ω;

[0094] B4) The double-sided thickness d of the safety coating and the value of the double-sided diaphragm resistance R under a pressure of 0.4t satisfy the condition: 2≤R×d≤50;

[0095] B5) Along the unwinding direction perpendicular to the current collector, the distance W between the left edge of the safety coating on surface A of the current collector and the left edge of the current collector. A1 The range is 2mm to 30mm, and the distance W between the right edge and the right edge of the current collector is... A2 The range is 3mm to 30mm; the distance W between the left edge of the safety coating on the B side of the current collector and the left edge of the current collector. B1 The range is 2mm to 30mm, and the distance W between the right edge and the right edge of the current collector is... B2 The range is 3mm to 30mm; and W B1 -W A1 ≥1mm, W B2 -W A2 ≥1mm.

[0096] In some embodiments of the present invention, the double-sided thickness d of the safety coating (i.e., the sum of the thicknesses of the safety coatings applied to both sides of the current collector surface) is 1 to 20 μm, for example, it can be 1 to 7 μm, 7 to 14 μm, or 14 to 20 μm.

[0097] In some embodiments of the present invention, the areal density of the safety coating (i.e., the sum of the areal densities of the safety coatings applied to both sides of the current collector surface) is 2–35 mg / 1540.25 mm. 2 For example, it can be 2-8 mg / 1540.25 mm. 2 8-15mg / 1540.25mm 2 14-21 mg / 1540.25 mm 2 20-28mg / 1540.25mm 2 28-35mg / 1540.25mm 2 .

[0098] There is a positive correlation between the coating density and thickness of the safety coating. If the thickness is too low, the safety performance of the battery cell will be poor; if the thickness is too high, it will reduce the energy density of the battery cell.

[0099] In some embodiments of the present invention, the double-sided diaphragm resistance R (i.e., the sum of the diaphragm resistances of the safety coating on both sides of the current collector surface) of the safety coating under a pressure of 0.4t is 0.5 to 5Ω, for example, it can be 0.5 to 2Ω, 2 to 3.5Ω, or 3.5 to 5Ω. The diaphragm resistance of the safety coating is the primary factor affecting the safety performance of the battery cell. If this value is too small, the safety performance of the battery cell will deteriorate, while if it is too large, the cycle performance of the battery cell will be worse. A value between 0.5 and 5Ω@0.4T can balance both safety performance and cycle performance.

[0100] In some embodiments of the present invention, the double-sided thickness d (in μm) of the safety coating and the double-sided film resistance R (in Ω) under a pressure of 0.4t satisfy the condition: 2 ≤ R × d ≤ 50. Generally, parameters R and d are positively correlated with the safety of the battery cell and negatively correlated with its cycle performance. When the relationship 2 ≤ R × d ≤ 50 is satisfied, a better balance can be achieved between the safety performance and electrochemical performance of the battery cell.

[0101] In some embodiments of the present invention, the adhesion strength between the safety coating and the current collector is not less than 100 N / m. If the adhesion strength is less than 100 N / m, the safety coating is at risk of detaching during subsequent use.

[0102] In one specific embodiment, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material layer, a safety coating, and a positive electrode current collector. The safety coating is made of inorganic fillers and a first binder; the non-uniformity coefficient C of the inorganic fillers is... u Satisfying 2≤C u ≤18, curvature coefficient C c Satisfying 0.5≤C c ≤3.1; The mass fraction w of the first adhesive in the safety coating satisfies w=k×(C u ) 0.5 / D v50 And 0.2≤k≤2; wherein, the non-uniformity coefficient C u The calculation formula is: C u =D v90 / D v10 The curvature coefficient C c The calculation formula is: C c =D v50 ×D v50 / (D v10 ×D v90 );D v10 D v50 D v90 , , represent the particle sizes corresponding to the cumulative volume distribution of inorganic fillers reaching 10%, 50%, and 90%, respectively; k is a constant related to the density of the inorganic filler.

[0103] The positive electrode sheet provided by this invention incorporates a safety coating comprising inorganic fillers and a binder. By limiting the particle size of the inorganic fillers, a particle size distribution is achieved, resulting in a denser structure for the safety coating. This reduces the probability of contact between the positive and negative electrodes, thereby improving the safety performance of the battery cell. Simultaneously, optimizing the amount of binder in the safety coating promotes electrolyte absorption, enhancing the rate performance, low-temperature discharge performance, and cycle performance of the battery cell.

[0104] A third aspect of the present invention provides a method for preparing the above-described electrode sheet, comprising the steps of:

[0105] S100. Mix the first adhesive with water and apply it to obtain an adhesive solution;

[0106] S200. Mix the first conductive agent and inorganic filler with the adhesive solution evenly, or mix the first conductive agent, thermally stable active material and inorganic filler with the adhesive solution evenly to obtain a safety coating slurry.

[0107] S300. The water-based safety coating slurry is coated onto one or both sides of the current collector, or onto the surface of the active material layer away from the current collector, to obtain the electrode sheet.

[0108] The electrode sheet preparation method according to embodiments of the present invention has at least the following beneficial effects: By introducing a safety coating into the electrode sheet and limiting the particle size of the inorganic filler and the content of the binder in the safety coating, the present invention can improve the safety performance of the battery cell while simultaneously improving the rate performance, low-temperature discharge performance, and cycle performance of the battery cell, without changing the original process. This method is not only simple in process but also has undemanding reaction conditions, is compatible with existing preparation processes, and has the potential for large-scale application.

[0109] In some embodiments of the present invention, the method for preparing the electrode sheet includes at least one of the following:

[0110] C1) The mass ratio of the first conductive agent, the first binder, and the inorganic filler is (0.5~5):(1~21.2):(73.8~98.5);

[0111] C2) The solid content of the adhesive solution is 10% to 30%;

[0112] C3) The viscosity of the adhesive solution is 1×10 3 ~3×10 4 mPa·s;

[0113] C4) The solid content of the safety coating slurry is ≥10%;

[0114] C5) The viscosity of the safety coating slurry is ≥50 mPa·s;

[0115] C6) The dyne value of the current collector is ≥30 dyn / cm;

[0116] C7) The safety coating slurry is applied to one or both sides of the current collector surface, or the surface of the active material layer away from the current collector surface, by gravure printing.

[0117] C8) When C7) is included, the oven temperature for gravure printing is 90-110℃ and the printing speed is 10-50m / min.

[0118] [Correction 27.12.2024 according to Rule 91] C9) The mass ratio of the first conductive agent, the first binder, the inorganic filler, and the heat-stabilized active substance is (0.5~5):(1~21.2):(1~97.5):(1~97.5).

[0119] In some embodiments of the present invention, the mass ratio of the first conductive agent, the first binder, and the inorganic filler is (0.5–5):(1–21.2):(73.8–98.5). For example, by weight, the first conductive agent may be 0.5–5 parts, the binder may be 1–21.2 parts, and the inorganic filler may be 73.8–98.5 parts.

[0120] In some embodiments of the present invention, the solid content of the adhesive is 10% to 30%, for example, it can be 10% to 20%, 20% to 25%, or 25% to 30%.

[0121] In some embodiments of the present invention, the viscosity of the adhesive is 1 × 10⁻⁶. 3 ~3×10 4 mPa·s, preferably 1.5 × 10 mPa·s. 4 ~2.5×10 4 mPa·s, more preferably 1.6 × 10 mPa·s. 4 ~2.2×10 4 mPa·s, for example, can be 2×10 4 mPa·s.

[0122] If the solid content and viscosity of the adhesive solution are too low, it will not only reduce processing efficiency, but may also lead to insufficient adhesion of the water-based safe coating; while if the solid content and viscosity are too high, it may lead to difficulties in processing the water-based safe coating.

[0123] In some embodiments of the present invention, the raw materials of the safety coating further include a heat-stabilized active substance, the mass ratio of which satisfies: first conductive agent: first binder: inorganic filler: heat-stabilized active substance = (0.5-5):(1-21.2):(1-97.5):(1-97.5). For example, by weight, the first conductive agent can be 0.5-5 parts, the binder can be 1-21.2 parts, the inorganic filler can be 1-97.5 parts, and the heat-stabilized active substance can be 1-97.5 parts.

[0124] In some embodiments of the present invention, the solid content of the safety coating slurry is ≥10%, preferably 10% to 21%.

[0125] In some embodiments of the present invention, the viscosity of the safety coating slurry is ≥50 mPa·s.

[0126] The solid content of the safety coating paste should be no less than 10%, and the viscosity should be no less than 50 mPa·s. Too low a solid content will not only reduce production efficiency, but also make it difficult to obtain a water-based safety coating with the specified thickness and areal density, while too low a viscosity will be detrimental to the gravure printing process.

[0127] In some embodiments of the present invention, the dyne value of the current collector is ≥30 dyn / cm, preferably ≥38 dyn / cm. When the dyne value of the current collector is lower than 30 dyn / cm, on the one hand, it is not conducive to the wetting of the current collector by the safety coating slurry, resulting in missed coating of the primer; on the other hand, it reduces the adhesion between the safety coating and the current collector, causing the safety coating to easily fall off during subsequent use, which adversely affects the safety of the battery cell. A dyne value of not less than 38 dyn / cm for the current collector ensures that the primer has a good appearance and that the adhesion between the safety coating and the current collector is good.

[0128] In some embodiments of the present invention, the safety coating slurry is applied to one or both surfaces of the current collector, or to the surface of the active material layer away from the current collector, by gravure printing.

[0129] In some embodiments of the present invention, the temperature of the oven is 90-110°C during gravure printing; the printing speed is not less than 10 m / min, preferably 10-50 m / min.

[0130] When performing gravure printing, the oven temperature should be 90–110℃, and the printing speed should be 10–50 m / min. An oven temperature below 90℃ will reduce production efficiency, while a temperature above 110℃ may cause problems such as cracking and conductive agent migration to the surface. Too low a printing speed will also reduce production efficiency, while too high a speed may lead to incomplete application of the safety coating, negatively impacting the safety performance of the battery cell.

[0131] In one specific embodiment of the present invention, a method for preparing the above-mentioned electrode sheet is provided, comprising the following steps:

[0132] (1) Using deionized water as a solvent, the first binder, the first conductive agent, and the inorganic filler are mixed evenly to obtain a safety coating slurry;

[0133] (2) The safety coating slurry obtained in step (1) is transferred to one or both sides of the current collector surface, or the surface of the active material layer away from the current collector surface, by gravure printing, to obtain an electrode sheet with the safety coating area and the non-safety coating area spaced apart along the unwinding direction of the electrode sheet.

[0134] In some embodiments of the present invention, the total length of the electrode sheet containing the safety coating is L, the length of the safety coating area is L1, the length of the non-safety coating area is L2, and L1 > L2, L1 + L2 = L.

[0135] In some embodiments of the present invention, a safety coating can be applied to both sides (surface A and surface B) of the electrode sheet, wherein the length of the safety coating area on surface A is L. A1 The length of the non-safety coating area is L A2 And LA1 >L A2 L A1 +L A2 =L A The length of the B-side coating area is L. B1 The length of the non-safety coating area is L B2 And L B1 >L B2 L B1 +L B2 =L B .

[0136] In some preferred embodiments of the present invention, in order to improve production efficiency and reduce costs, both LA2 and LB2 can be set to 0, i.e., L A1 =L B1 =L A =L B .

[0137] In some embodiments of the present invention, when applying the safety coating, N1 slots for electrode tab welding need to be reserved in the safety coating area or non-safety coating area along the unwinding direction of the electrode sheet, where N1≥0.

[0138] In some embodiments of the present invention, when applying the safety coating, N2 slots for electrode tab welding are reserved in the safety coating area or non-safety coating area perpendicular to the electrode sheet unwinding direction, where N2≥0.

[0139] In some embodiments of the present invention, when applying the safety coating, N3 safety coatings can also be applied simultaneously along the unwinding direction of the electrode sheet, where N3 ≥ 1.

[0140] In some embodiments of the present invention, if both sides of the electrode sheet are coated with a safety coating, when reserving slots for electrode tab welding, the slots on the A / B sides must be kept opposite each other, and the misalignment distance ΔW in both the lateral and longitudinal directions shall not exceed 2mm.

[0141] In some embodiments of the present invention, if both sides of the electrode sheet are coated with a safety coating, then along the unwinding direction perpendicular to the current collector, the distance from the left edge of the water-based safety layer on surface A to the left edge of the current collector is W. A1 (i.e., the blank space on the left side of side A is W) A1 The right side of side A is left blank as W. A2 The blank space on the left side of side B is W. B1 The right side of side B is left blank as W. B2 Satisfying 2mm≤W A1 W A2 W B1 W B2 ≤30mm, and W B1 -W A1≥1mm, W B2 -W A2 ≥1mm.

[0142] In some embodiments of the present invention, the electrode sheet is a positive electrode sheet, and the method for preparing the positive electrode sheet includes the following steps:

[0143] (10) Using deionized water as a solvent, add binder to make a glue solution with appropriate viscosity and solid content, then add the first conductive agent and inorganic filler to the glue solution and mix evenly, or mix the first conductive agent, heat-stabilized active material and inorganic filler with the glue solution evenly to obtain a water-based safe coating slurry.

[0144] (20) The safety coating slurry obtained in step (10) is transferred to one or both sides of the current collector by gravure printing to obtain a positive electrode sheet with the safety coating area and the non-safety coating area spaced apart along the unwinding direction of the current collector.

[0145] The non-safety coating area corresponds to the head and / or tail of the positive electrode sheet of the battery cell. Typically, one side is active material, and the other side is empty foil, or a separate ceramic layer. This ceramic layer usually contains only inorganic fillers and binders, which can reduce the generation of burrs on the positive electrode current collector during battery cell testing and lower the probability of the positive electrode current collector coming into contact with the negative electrode active material, thereby improving the battery cell's safety performance. However, this ceramic layer requires an additional coating process after the safety coating is applied, which not only reduces production efficiency but also increases production costs.

[0146] In some embodiments of the present invention, the total length of the positive electrode sheet containing the safety coating is L, the length of the safety coating area is L1, the length of the non-aqueous safety coating area is L2, and L1 > L2, L1 + L2 = L.

[0147] In some embodiments of the present invention, a safety coating can be applied to both sides (surface A and surface B) of the positive electrode, wherein the length of the safety coating area on surface A is L. A1 The length of the non-safety coating area is L A2 And L A1 >L A2 L A1 +L A2 =L A The length of the safety coating area on side B is L. B1 The length of the non-safety coating area is L B2 And L B1 >L B2 L B1 +L B2 =L B .

[0148] In some preferred embodiments of the present invention, to improve production efficiency and reduce costs, the function of the ceramic layer can be assumed by a safety coating, that is, a safety coating can also be provided in the non-safety coating areas. A2 and L B2 All are set to 0, that is, L A1 =L B1 =L A =L B .

[0149] Figure 2 shows a cross-sectional view of the current collector coated with a safety coating along the unwinding direction in one specific embodiment of the present invention. In the figure, 02-positive electrode sheet; 021-reserved slot; 022-current collector; 023-safety coating area; 024-non-safety coating area. The safety coating area and non-safety coating area on side A and side B of the positive electrode sheet can be arranged opposite each other, as shown in Figure (a); alternatively, one side can be a non-safety coating area and the other side a safety coating area, as shown in Figure (b). The total length of the current collector containing the safety coating is L, and the length of the safety coating area on side B is L. B1 The length of the non-safety coating area is L B2 And L B1 >L B2 L B1 +L B2 =L B =L A1 =L A =L; A safety coating can also be applied to areas that are not normally covered by a safety coating, L A2 and L B2 All are set to 0, that is, L A1 =L B1 =L A =L B As shown in Figure (c).

[0150] In some embodiments of the present invention, when applying the safety coating, Z slots for electrode tab welding need to be reserved in the safety coating area or non-safety coating area along the unwinding direction of the current collector, where Z≥0.

[0151] In some embodiments of the present invention, when applying the safety coating, X slots for electrode tab welding need to be reserved in the safety coating area or non-safety coating area perpendicular to the unwinding direction of the current collector, where X ≥ 0.

[0152] In some embodiments of the present invention, when applying the safety coating, Y safety coatings can also be applied simultaneously along the unwinding direction of the current collector, where Y ≥ 1.

[0153] When applying the safety coating, the present invention may or may not reserve slots for electrode tab welding as needed, as shown in Figure 3.

[0154] In some embodiments of the present invention, if both sides of the current collector are coated with a safety coating, the slots reserved for electrode welding must be kept so that the slots on the A and B sides are opposite each other, and the misalignment ΔW in the lateral and longitudinal directions does not exceed 2mm.

[0155] In some embodiments of the present invention, the safety coating is applied to both sides of the current collector, and along the unwinding direction perpendicular to the current collector, the distance W between the left edge of the safety coating on side A of the current collector and the left edge of the current collector is... A1 The range is 2mm to 30mm, and the distance W between the right edge and the right edge of the current collector is... A2 The range is 2mm to 30mm; the distance W between the left edge of the safety coating on the B side of the current collector and the left edge of the current collector. B1 The range is 2mm to 30mm, and the distance W between the right edge and the right edge of the current collector is... B2 The range is 2mm to 30mm; and W B1 -W A1 ≥1mm, W B2 -W A2 ≥1mm. That is, if both sides of the current collector are coated with a safety coating, then along the unwinding direction perpendicular to the current collector, the distance from the left edge of the safety coating on side A to the left edge of the current collector is W. A1 (i.e., the blank space on the left side of side A is W) A1 The right side of side A is left blank as W. A2 The blank space on the left side of side B is W. B1 The right side of side B is left blank as W. B2 Satisfying 2mm≤W A1 W A2 ≤30mm, 3mm≤W B1 W B2 ≤30mm, and W B1 -W A1 ≥1mm, W B2 -W A2 ≥1mm. Figure 4 shows a cross-sectional view of the safety coating perpendicular to the unwinding direction in a specific embodiment of the present invention. In the figure, 021-reserved slot; 022-current collector; 023-safety coating area; this setting allows the width of the safety coating on side A to be more than 2mm wider than that on side B, thereby reducing the bulging of the edge when the primer is wound up.

[0156] In a fourth aspect, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode; wherein the positive electrode and / or the negative electrode is an electrode sheet as described above or an electrode sheet obtained by the preparation method described above.

[0157] Since the lithium-ion battery adopts all the technical solutions of the electrode sheets in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions in the above embodiments. Specifically, by introducing a safety coating into the electrode sheets and limiting the particle size of the inorganic filler in the safety coating to achieve particle size distribution, the lithium-ion battery can achieve a denser structure in the safety coating, reducing the probability of contact between the positive and negative electrodes, thereby improving the safety performance of the cell. Simultaneously, optimizing the amount of binder in the safety coating promotes the absorption of electrolyte by the safety coating, improving the rate performance, low-temperature discharge performance, and cycle performance of the cell.

[0158] In some embodiments of the present invention, the positive electrode sheet is an electrode sheet as described above. The positive electrode sheet includes a positive current collector containing a safety coating and a positive active material layer coated on at least one surface of the positive current collector. The positive current collector is a commonly used positive current collector in the art, such as aluminum foil, but is not limited thereto. The positive active material layer includes a positive active material, which is a commonly used positive active material in lithium-ion batteries, including but not limited to chemical formulas such as Li. x Ni h Co y M z O 2-d N d (where 0.95≤x≤1.2, h>0, y≥0, z≥0, and h+y+z=1, 0≤d≤1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The positive electrode active material can be one or more combinations thereof, including O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2. The positive electrode active material can also be modified. Methods for modifying the positive electrode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the positive electrode active material. The materials used for modification can be one or more combinations thereof, including but not limited to Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W.

[0159] In some embodiments of the present invention, the negative electrode sheet is an electrode sheet as described above. The negative electrode sheet includes a negative current collector containing a safety coating and a negative active material layer coated on at least one surface of the negative current collector. The negative current collector has no special requirements and can be copper foil commonly used in the industry. The negative active material layer includes a negative active material, which includes silicon-based materials, selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys, or a mixture of silicon negative electrode materials and other commonly used negative active materials. These other negative active materials include, but are not limited to, graphite, soft carbon, hard carbon, carbon fibers, mesophase carbon microspheres, tin-based materials, lithium titanate, or other metals capable of forming alloys with lithium. The graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0160] In some embodiments of the present invention, the separator can be any material suitable for lithium-ion battery separators in the art, such as, but not limited to, one or more combinations of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers. In actual production, the material and structure of the separator are not strictly limited. For example, it can be a multilayer structure formed by stacking the above materials, a single-layer structure formed by mixing the above materials, or a single-layer structure formed by a single material; as long as it can perform the basic function of a separator, it is acceptable.

[0161] In some embodiments of the present invention, the lithium battery further includes an electrolyte that wets the positive electrode, negative electrode, and separator. The electrolyte includes an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or it can be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DEC, DMC, or EMC; or it can be a carboxylic acid ester, including PP, MA, EA, EP, etc. The additives include, but are not limited to, at least one of the following: film-forming additives, conductive additives, flame-retardant additives, overcharge prevention additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and water-based safety additives.

[0162] This invention also proposes a secondary battery, comprising a positive electrode, a negative electrode, and a separator spaced between the positive and negative electrode; the positive electrode and / or the negative electrode is an electrode sheet as described above or an electrode sheet obtained by the preparation method described above. The electrode sheet proposed in this invention can be applied not only to the aforementioned lithium-ion battery but also to other secondary batteries, including sodium-ion batteries, potassium-ion batteries, etc., without any limitations.

[0163] In a fifth aspect, the present invention provides an application of the above-described lithium-ion battery in an energy storage device, an electrical appliance, or an electronic device. Attached Figure Description

[0164] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0165] Figure 1 is a schematic diagram of the structure of the positive electrode sheet containing a safety coating provided by the present invention, wherein, 01-positive electrode sheet; 011-active material layer; 022-current collector; 023-safety coating;

[0166] Figure 2 is a schematic cross-sectional view of the current collector containing a safety coating provided by the present invention along the unwinding direction, wherein 02-positive current collector containing safety coating; 021-reserved slot; 022-current collector; 023-safety coating; 024-non-safety coating area;

[0167] Figure 3 is a top view of the current collector (unstripped state) containing a safety coating provided by the present invention;

[0168] Figure 4 is a schematic cross-sectional view of the current collector containing a safety coating provided by the present invention along the unwinding direction, wherein 021-reserved slot; 022-current collector; 023-safety coating. Detailed Implementation

[0169] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0170] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0171] In the description of this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. Unless otherwise stated, the various reaction or operation steps may be performed sequentially or not. Preferably, the reaction methods in this invention are performed sequentially.

[0172] Unless otherwise specified in the following examples, the techniques or conditions described in the literature in this field or in accordance with the product instructions shall apply. All reagents or instruments without a specified manufacturer are commercially available conventional products.

[0173] Example 1

[0174] This embodiment provides a lithium-ion battery, the positive electrode of which contains a safety coating, the safety coating comprising a first binder, a first conductive agent Super P Li and an inorganic filler boehmite;

[0175] The structural formula of the first adhesive is:

[0176] (1) Preparation of the first adhesive:

[0177] a) Add 1000 parts by weight of distilled water to the reaction vessel, start stirring, purge with high-purity nitrogen to remove oxygen for 1 hour, then add 50 parts by weight of acrylonitrile, 35 parts by weight of lithium acrylate and 15 parts by weight of methyl acrylate, heat to 65°C under an inert atmosphere and keep the temperature constant.

[0178] b) Then add 5 parts by weight of 20% ammonium persulfate solution as an initiator to initiate the reaction, and react for 5 hours;

[0179] c) After the reaction is complete, the mixture is filtered, dried, pulverized, and sieved to obtain the binder. The binder contains 50% -CN (n1), 35% -COOLi (n2), and 15% -COOCH3 (n3), with a weight-average molecular weight M... w 3.6×10 5 Number average molecular weight M w 2.0×10 5M w / M n =1.8, electrolyte absorption rate c =22.7%.

[0180] (2) Preparation of positive electrode current collector with safety coating:

[0181] [Corrected according to Rule 91, December 27, 2024] Using deionized water as a solvent, add 10 parts of the above-mentioned adhesive for bonding, adjusting the amount of deionized water until a solid content of 15% and a viscosity of 2.2 × 10⁻⁶ are obtained. 4 The adhesive solution was prepared at mPa·s; then 88 parts of the inorganic filler boehmite (D) were added. v10 D v50 D v90 The thicknesses are 0.2 μm, 0.4 μm, and 0.9 μm, respectively, and C u =4.5, C c =0.89, specific surface area is 9.5m² 2 (g) and 2 parts of the first conductive agent Super P Li were mixed evenly to obtain a safety coating slurry with a solid content of 20% and a viscosity of 750 mPa·s. The safety coating slurry was coated onto both sides of the aluminum foil by gravure printing. During coating, L A2 and L B2 All are set to 0, that is, L A1 =L B1 =L A =L B =L, Z=Y=1, X=4. Furthermore, the oven temperature during printing needs to be set to 95℃, and the printing speed to 30m / min, ultimately obtaining a positive current collector with a double-sided safety coating. The double-sided coating surface density of the safety coating is 10.3mg / 1540.25mm². 2 The double-sided thickness is 5.3μm, the double-sided film resistance is 3.1Ω@0.4T, and the adhesion between the safety coating and the current collector is 1356N / m.

[0182] (3) Preparation of positive electrode sheet:

[0183] A positive electrode slurry with a solid content of 75% and a viscosity of 7000 mPa·s is prepared by uniformly mixing positive electrode active material, conductive agent (a mixture of conductive carbon black and carbon nanotubes, with a mass ratio of 6:5), PVDF binder, and NMP at a mass ratio of 97.6:1.1:1.3:35. The positive electrode slurry is coated onto one side of the current collector aluminum foil containing the safety coating, dried and wound at 85°C, and then coated and dried on the other side of the current collector aluminum foil using the same method. The positive electrode sheet with positive electrode active material layers on both sides is then cold-pressed; subsequently, it is trimmed and slit to produce a lithium-ion battery positive electrode sheet (film resistance of 0.8Ω@0.4t).

[0184] (4) Preparation of negative electrode sheet:

[0185] Using water as a solvent, graphite, thickener, and SBR binder were mixed evenly at a mass ratio of 97.7:1.1:1.2 to prepare a lithium-ion battery negative electrode slurry with a solid content of 50% and a viscosity of 5000 mPa·s. The slurry was coated on one side of the current collector copper foil and dried and rolled up at 80°C. Then, the negative electrode slurry was coated and dried on the other side of the copper foil in the same way to obtain a negative electrode sheet with active material coated on both sides.

[0186] (5) Preparation of electrolyte:

[0187] Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent of dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (mass ratio of DMC, EC, and EMC was 3:5:2) to obtain the electrolyte.

[0188] (6) Battery fabrication:

[0189] The prepared positive electrode, negative electrode, and separator are wound into a battery cell with a capacity of approximately 5Ah. The separator is located between adjacent positive and negative electrode sheets. The positive electrode is led out by spot welding with aluminum tabs, and the negative electrode is led out by spot welding with nickel tabs. The battery cell is then placed in an aluminum-plastic packaging bag, baked, and then injected with the electrolyte. After encapsulation, formation, and capacity testing, a lithium-ion battery is finally produced.

[0190] Example 2

[0191] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 96.94 parts (D). v10 D v50 D v90 The thicknesses are 0.2 μm, 0.4 μm, and 0.9 μm, respectively, and C u =4.5, C c =0.89), the number of parts of the first adhesive is 1.06 parts (the mass fraction w of the first adhesive in the safety coating satisfies w = k × (C u ) 0.5 / D v50 (k = 0.2), the first conductive agent Super P Li is in 2 parts.

[0192] The rest is the same as in Example 1, and will not be repeated here.

[0193] Example 3

[0194] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 87.39 parts (D). v10 D v50 D v90The thicknesses are 0.2 μm, 0.4 μm, and 0.9 μm, respectively, and C u =4.5, C c =0.89), the number of parts of the first adhesive is 10.61 parts (the mass fraction w of the first adhesive in the safety coating satisfies w = k × (C u ) 0.5 / D v50 (k=2), the first conductive agent Super P Li is in 2 parts.

[0195] The rest is the same as in Example 1, and will not be repeated here.

[0196] Example 4

[0197] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 76.79 parts (D). v10 D v50 D v90 The thicknesses are 0.1 μm, 0.4 μm, and 1.8 μm, respectively, and C u =18, C c =0.89), the number of parts of the first adhesive is 21.21 parts (the mass fraction w of the first adhesive in the safety coating satisfies w = k × (C u ) 0.5 / D v50 (k=2), the first conductive agent Super P Li is in 2 parts.

[0198] The rest is the same as in Example 1, and will not be repeated here.

[0199] Example 5

[0200] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 77.95 parts (D). v10 D v50 D v90 The thicknesses are 0.1 μm, 0.4 μm, and 1.8 μm, respectively, and C u =18, C c =0.89), the number of parts of the first adhesive is 20.05 parts (the mass fraction of the first adhesive in the safety coating, w, satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0201] The rest is the same as in Example 1, and will not be repeated here.

[0202] Example 6

[0203] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 84.64 parts (D).v10 D v50 D v90 The thicknesses are 0.15 μm, 0.4 μm, and 1.2 μm, respectively, and C u =8, C c =0.89), the number of parts of the first adhesive is 13.36 parts (the mass fraction of the first adhesive in the safety coating, w, satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0204] The rest is the same as in Example 1, and will not be repeated here.

[0205] Example 7

[0206] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 91.32 parts (D). v10 D v50 D v90 The thicknesses are 0.3 μm, 0.4 μm, and 0.6 μm, respectively, and C u =2, C c =0.89), the number of parts of the first adhesive is 6.68 parts (the mass fraction of the first adhesive in the safety coating, w, satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0207] The rest is the same as in Example 1, and will not be repeated here.

[0208] Example 8

[0209] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 84.64 parts (D). v10 D v50 D v90 The thicknesses are 0.2 μm, 0.3 μm, and 0.9 μm, respectively, and C u =4.5, C c =0.5), the number of parts of the first adhesive is 13.36 parts (the mass fraction of the first adhesive in the safety coating w satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0210] The rest is the same as in Example 1, and will not be repeated here.

[0211] Example 9

[0212] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 91.32 parts (D). v10 D v50 D v90 The thicknesses are 0.2 μm, 0.6 μm, and 0.9 μm, respectively, and C u =4.5, C c =2), the number of parts of the first adhesive is 6.68 parts (the mass fraction of the first adhesive in the safety coating w satisfies w = w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0213] The rest is the same as in Example 1, and will not be repeated here.

[0214] Example 10

[0215] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 92.58 parts (D). v10 D v50 D v90 The thicknesses are 0.2 μm, 0.74 μm, and 0.9 μm, respectively, and C u =4.5, C c =3.04), the number of parts of the first adhesive is 5.42 parts (the mass fraction of the first adhesive in the safety coating, w, satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0216] The rest is the same as in Example 1, and will not be repeated here.

[0217] Example 11

[0218] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 77.95 parts (D). v10 D v50 D v90 The thicknesses are 0.1 μm, 0.2 μm, and 0.45 μm, respectively, and C u =4.5, C c =0.89), the number of parts of the first adhesive is 20.05 parts (the mass fraction of the first adhesive in the safety coating, w, satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0219] The rest is the same as in Example 1, and will not be repeated here.

[0220] Example 12

[0221] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 97 parts (D). v10 D v50 D v90 They are 2μm, 4μm, and 9μm respectively, C u =4.5, C c =0.89), the number of parts of the first adhesive is 1 part (the mass fraction w of the first adhesive in the safety coating satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0222] The rest is the same as in Example 1, and will not be repeated here.

[0223] Example 13

[0224] The difference from Example 1 is that the first adhesive is replaced with PVDF adhesive, and the solvent is replaced with NMP (N-methylpyrrolidone) instead of deionized water.

[0225] The rest is the same as in Example 1, and will not be repeated here.

[0226] Example 14

[0227] The difference from Example 1 is that: during coating, a separate ceramic layer is provided in the non-water-based safety coating area on surface B, i.e., L B2 ≠0, as shown in Figure 3, the total length of the current collector containing the water-based safety coating is L, and the length of the water-based safety coating area on surface B is L. B1 The length of the non-water-based safety coating area is L. B2 And L B1 >L B2 L B1 +L B2 =L B =L A1 =L A =L.

[0228] The rest is the same as in Example 1, and will not be repeated here.

[0229] Comparative Example 1

[0230] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 72.94 parts (D). v10 D v50 D v90 The thicknesses are 0.08 μm, 0.4 μm, and 2.25 μm, respectively, and C u=28.1, C c =0.89), the number of parts of the first adhesive is 25.06 parts (the mass fraction of the first adhesive in the safety coating w satisfies w = w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0231] The rest is the same as in Example 1, and will not be repeated here.

[0232] Comparative Example 2

[0233] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 92.24 parts (D). v10 D v50 D v90 The thicknesses are 0.35 μm, 0.4 μm, and 0.52 μm, respectively, and C u =1.5, C c =0.88), the number of parts of the first adhesive is 5.76 parts (the mass fraction of the first adhesive in the safety coating, w, satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0234] The rest is the same as in Example 1, and will not be repeated here.

[0235] Comparative Example 3

[0236] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 83.15 parts (D). v10 D v50 D v90 The thicknesses are 0.2 μm, 0.27 μm, and 0.9 μm, respectively, and C u =4.5, C c =0.41), the number of parts of the first adhesive is 14.85 parts (the mass fraction of the first adhesive in the safety coating, w, satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0237] The rest is the same as in Example 1, and will not be repeated here.

[0238] Comparative Example 4

[0239] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 93 parts (D). v10 D v50 Dv90 The thicknesses are 0.2 μm, 0.8 μm, and 0.9 μm, respectively, and C u =4.5, C c =3.56), the number of parts of the first adhesive is 5 (the mass fraction w of the first adhesive in the safety coating satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0240] The rest is the same as in Example 1, and will not be repeated here.

[0241] Comparative Example 5

[0242] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 85.47 parts (D). v10 D v50 D v90 The thicknesses are 0.08 μm, 0.8 μm, and 2.25 μm, respectively, and C u =28.1, C c =3.56), the number of parts of the first adhesive is 12.53 parts (the mass fraction of the first adhesive in the safety coating, w, satisfies w = k × (C u ) 0.5 / D v50 (k = 1.89), the first conductive agent Super P Li is in 2 parts.

[0243] The rest is the same as in Example 1, and will not be repeated here.

[0244] Comparative Example 6

[0245] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 97.47 parts (D). v10 D v50 D v90 The thicknesses are 0.2 μm, 0.4 μm, and 0.9 μm, respectively, and C u =4.5, C c =0.89), the number of parts of the first adhesive is 0.53 parts (the mass fraction of the first adhesive in the safety coating, w, satisfies w = k × (C u ) 0.5 / D v50 (k=0.1), the first conductive agent Super P Li is 2 parts.

[0246] The rest is the same as in Example 1, and will not be repeated here.

[0247] Comparative Example 7

[0248] The difference from Example 1 is that the proportion of the inorganic filler boehmite is 74.14 parts (D). v10 D v50 D v90 The thicknesses are 0.2 μm, 0.4 μm, and 0.9 μm, respectively, and C u =4.5, C c =0.89), the number of parts of the first adhesive is 23.86 parts (the mass fraction of the first adhesive in the safety coating, w, satisfies w = k × (C u ) 0.5 / D v50 (k=4.5), the first conductive agent Super P Li is 2 parts.

[0249] The rest is the same as in Example 1, and will not be repeated here.

[0250] Comparative Example 8

[0251] The difference from Example 1 is that the surface of the positive current collector is not coated with a safety coating.

[0252] The rest is the same as in Example 1, and will not be repeated here.

[0253] Test case

[0254] To verify the effect of the safety coating introduced in this invention on the performance of the battery cell, the particle size of the inorganic filler, the electrolyte absorption rate c of the binder, the double-sided film resistance of the safety coating, as well as the needle penetration, low-temperature discharge performance, rate performance and cycle performance of the battery cell were tested.

[0255] Particle size testing method: Inorganic fillers were dispersed with water as a dispersant, and the particle size of inorganic fillers was tested using a laser particle size analyzer (Malvin, Mastersizer3000).

[0256] Electrolyte absorption rate (c) test method: The adhesive solution is poured into a polytetrafluoroethylene (PTFE) pan and baked to evaporate the deionized water, thus obtaining an adhesive polymer film with a thickness controlled at 100 μm. The film is then cut into sheets 50 mm long × 50 mm wide. After vacuum drying for 24 hours, the film is weighed. The completely dried film is then immersed in an electrolyte solution at 80°C for 12 hours. After removing the film and wiping off the electrolyte adhering to its surface, the weight of the film after absorbing the electrolyte is measured. The percentage increase in weight of the film before and after immersion in the electrolyte is the electrolyte absorption rate of the adhesive at 80°C.

[0257] Diaphragm resistance test method: The instrument used for diaphragm resistance testing is the ACCFILM diaphragm resistance testing system (model TT-ACCF-G2A) from Hangzhou Chuanyuan Technology Co., Ltd. The pressure during testing is 0.4t, and the pressure holding time is 10s.

[0258] Needle penetration test method: Charge the battery cell to 4.45V at a constant current and constant voltage of 1.0C at room temperature, with a cutoff rate of 0.05C. Then, perform a needle penetration test on the fully charged cell with the pitted side of the cell facing upwards. Use a steel nail with a diameter of 4.0mm to completely pierce the cell in one go at a speed of 40mm / s. The nail should be placed at the left, center, and right positions of the largest surface of the cell (5 cells at each position). Keep the test for 1 hour. If the cell does not catch fire or explode, it passes the test.

[0259] Low-temperature discharge performance test method: Discharge to 3V with a constant current of 1C and rest for 5 minutes; set the temperature chamber to 25℃ and rest for 60 minutes; charge to 4.45V with a constant current and constant voltage of 1.0C and a cutoff rate of 0.02C; rest for 5 minutes; discharge to 3V with a constant current of 0.2C and record the capacity at 3V at 0.2C as the initial capacity C0; set the temperature chamber to 25℃ and rest for 60 minutes; charge to 4.45V with a constant current and constant voltage of 1.0C and a cutoff rate of 0.02C; rest for 5 minutes; set the temperature chamber to -10℃ and rest for 120 minutes; then discharge the cell to 3.0V with a constant current of 0.2C and record the capacities C1 and C2 at 3.4V and 3.0V respectively. The ratio of C1 to C0 is the capacity retention rate at -10℃ to 3.4V.

[0260] Rate discharge performance test method: Discharge to 3V at 1C constant current and rest for 5 minutes; charge to 4.45V at 1.0C constant current and constant voltage, cut off rate at 0.02C, and rest for 5 minutes; discharge to 3V at 0.2C constant current and record the capacity at 3V at 0.2C as the initial capacity C3; charge to 4.45V at 1.0C constant current and constant voltage, cut off rate at 0.02C, and rest for 5 minutes; then discharge the cell to 3.0V at 0.2C and record the capacities C4 and C5 at 3.4V and 3.0V respectively. The ratio of C4 to C3 is the capacity retention rate when discharging to 3.4V at 2C.

[0261] Cyclic performance test method: Under an ambient temperature of 25±2℃, the cell is discharged to 3.0V at a constant current of 0.2C, and then charged to 4.45V at a constant current and constant voltage of 3C, with a cutoff rate of 0.05C. The voltage, internal resistance, capacity, and thickness (600g PPG for thickness measurement) of the cell at the first full charge are recorded. The cycling process is performed according to the following HFC standard: discharge to 3V at a constant current of 0.2C; charge to 4.25V at a constant current of 3.0C; charge to 4.25V at a constant current of 2.5C; charge to 4.45V at a constant current of 2.0C; charge to 4.50V at a constant current and constant voltage of 1.4C, with a cutoff rate of 0.3C; charge to 4.45V at a constant current and constant voltage of 2A, with a cutoff rate of 0.05C; discharge to 3V at a constant current of 1.0C. Completing the above steps constitutes one cycle. After 49 cycles, perform low-current recovery as follows: charge at a constant current of 3.0C to 4.25V; charge at a constant current of 2.5C to 4.25V; charge at a constant current of 2.0C to 4.45V; charge at a constant current and voltage of 1.4C to 4.50V, with a cutoff rate of 0.3C; charge at a constant current and voltage of 2A to 4.45V, with a cutoff rate of 0.05C; discharge at a constant current of 0.2C to 3V; charge at a constant current and voltage of 3.0C to 4.45V, with a cutoff rate of 0.05C. Record the fully charged cell voltage, internal resistance, and thickness (thickness measurement using 600g PPG) every 100 cycles.

[0262] The parameter settings and test results of Examples 1-14 and Comparative Examples 1-8 are shown in Table 1 below:

[0263] Table 1

[0264] As can be seen from the comparison of the test results in the table above, compared with Comparative Examples 1-8, the particle size D of the inorganic filler in the safety coating in Examples 1-14 is... v10 D v50 D v90 Satisfying 2≤Cu=D v90 / D v10 ≤18, 0.5≤C c =D v50 ×D v50 / (D v10 ×D v90 If )≤3.1, the amount of adhesive w satisfies: w=k×(C u ) 0.5 / D v50 0.2≤k≤2, where k is a constant related to the density of inorganic filler, which significantly improves the safety performance of the battery cell, increases the needle penetration test pass rate from 0% to 100%, and significantly improves the low temperature discharge performance, rate discharge performance and cycle performance.

[0265] In summary, the safety coating provided by this invention, by limiting the particle size of the inorganic filler and selecting the appropriate binder, can improve the safety performance of the battery cell while simultaneously enhancing its rate performance, low-temperature discharge performance, and cycle performance. Specifically, the particle size D of the inorganic filler... v10 D v50 D v90 It should satisfy 2≤Cu=D v90 / D v10 ≤18, 0.5≤C c =D v50 ×D v50 / (D v10 ×D v90 )≤3.1, C u and C c These are the non-uniformity coefficient and curvature coefficient of the inorganic packing, respectively, D. v10 D v50 D v90 These represent the particle sizes corresponding to cumulative volume distribution values ​​of inorganic fillers reaching 10%, 50%, and 90%, respectively. When the particle size of the inorganic filler satisfies the above relationship, its gradation curve exhibits good continuity, with a good gradation of fine and coarse particles. This allows the safety coating to have a relatively dense structure, thereby reducing the probability of short circuits between the positive and negative electrodes and improving the safety performance of the battery cell. The mass fraction w of the first binder should satisfy w = k × (C u ) 0.5 / D v50 For a given condition 0.2 ≤ k ≤ 2, when k is within the above range, the binder not only provides sufficient adhesion and reduces cell polarization, but also promotes the absorption of electrolyte by the safety coating, improving the cell's rate performance, low-temperature discharge performance, and cycle performance. Ultimately, the safety coating provided by this invention, by limiting the particle size of the inorganic filler, achieves a particle size distribution, resulting in a denser structure that reduces the probability of positive and negative electrode contact, thereby improving the cell's safety performance. Simultaneously, optimizing the amount of binder in the safety coating promotes electrolyte absorption, further enhancing the cell's rate performance, low-temperature discharge performance, and cycle performance. The cell provided by this invention, when satisfying the above relationships, can achieve a 100% needle penetration pass rate, a capacity retention rate of no less than 88% after 800 cycles at 25°C, a discharge capacity of no less than 70%@3.4V at -10°C, and a discharge capacity of no less than 70%@3.4V at 2.0C.

[0266] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A safety coating, characterized in that, The raw materials for the safety coating include inorganic fillers and a first binder; The non-uniformity coefficient C of the inorganic filler u Satisfying 2≤C u ≤18, curvature coefficient C c Satisfying 0.5≤C c ≤3.1; The mass fraction w of the first adhesive in the safety coating satisfies w = k × (C u ) 0.5 / D v50 And 0.2≤k≤2, where k is a constant; Wherein, the non-uniformity coefficient C u The calculation formula is: C u =D v90 / D v10 The curvature coefficient C c The calculation formula is: C c =D v50 ×D v50 / (D v10 ×D v90 ); D v10 D v50 D v90 These represent the particle sizes corresponding to the cumulative volume distribution of inorganic fillers reaching 10%, 50%, and 90%, respectively.

2. The safety coating according to claim 1, characterized in that, The median particle size D of the inorganic filler v50 The range is 0.2–4 μm, and the specific surface area is 5–50 m². 2 / g; And / or, the inorganic filler includes one or more of alumina, boehmite, aluminum hydroxide, magnesium hydroxide, silicon dioxide, titanium dioxide, lithium iron phosphate, lithium manganese iron phosphate, lithium titanium aluminum phosphate, lithium lanthanum titanate, or lithium lanthanum zirconium oxide. And / or, the mass fraction of inorganic filler in the safety coating is 73.8% to 98.5%.

3. The safety coating according to claim 1, characterized in that, The first adhesive includes one or more of polyvinylidene fluoride adhesive, sodium carboxymethyl cellulose adhesive, or polyacrylate adhesive; And / or, the mass fraction of the first binder in the safety coating is 1% to 21.2%.

4. The safety coating according to claim 3, characterized in that, The first adhesive is a polyacrylate adhesive, and the structural formula of the polyacrylate adhesive is as follows: Each time R1 appears, it is independently selected from H, Li, or Na; Each occurrence of R2 is independently selected from substituted or unsubstituted C1 to C2. 10 Alkyl groups; And 5≤(x+z) / y≤20, 1.2≤z / x≤2, and x, y, and z are all not 0; And / or, the weight-average molecular weight M of the polyacrylate adhesive w The range is 200,000 to 500,000, with a number-average molecular weight M. n The range is 100,000 to 400,000; And / or, the weight-average molecular weight M of the polyacrylate adhesive w Number-average molecular weight M n The proportion M w / M n ≤3; And / or, the polyacrylate adhesive has an electrolyte absorption rate of 10% to 50% at 80°C.

5. The safety coating according to any one of claims 1-4, characterized in that, The raw material of the safety coating also includes a first conductive agent; the safety coating satisfies at least one of the following: A1) The mass fraction of the first conductive agent in the safety coating is 0.5% to 5%; A2) The mass ratio of the first conductive agent, the first binder, and the inorganic filler is (0.5~5):(1~21.2):(73.8~98.5); A3) The raw materials for the safety coating also include heat-stabilized active substances; A4) When A3) is included, the mass ratio of the first conductive agent, the first binder, the inorganic filler, and the thermally stable active substance is (0.5~5):(1~21.2):(1~97.5):(1~97.5); A5) When A3) is included, the thermally stable active material includes one or both of lithium iron phosphate and lithium manganese iron phosphate.

6. An electrode sheet, characterized in that, include: current collector; Active material layer; The safety coating as described in any one of claims 1-5.

7. The electrode sheet according to claim 6, characterized in that, The safety coating is applied to at least one side of the current collector, and the active material layer is applied to the side of the safety coating away from the current collector and / or to the side of the current collector away from the safety coating; Alternatively, the active material layer is coated on at least one side of the current collector, and the safety coating is coated on the side of the active material layer away from the current collector and / or on the side of the current collector away from the active material layer.

8. The electrode sheet according to claim 7, characterized in that, The safety coating is applied to both surfaces of the current collector; the safety coating satisfies at least one of the following: B1) The thickness of the safety coating on both sides is 1–20 μm; B2) The double-sided coating surface density of the safety coating is 2–35 mg / 1540.25 mm². 2 ; B3) The double-sided diaphragm resistance of the safety coating tested under 0.4t pressure is 0.5~5Ω; B4) The double-sided thickness d of the safety coating and the value of the double-sided diaphragm resistance R under a pressure of 0.4t satisfy the condition: 2≤R×d≤50; B5) Along the unwinding direction perpendicular to the current collector, the distance W between the left edge of the safety coating on surface A of the current collector and the left edge of the current collector. A1 The range is 2mm to 30mm, and the distance W between the right edge and the right edge of the current collector is... A2 The range is 3mm to 30mm; the distance W between the left edge of the safety coating on the B side of the current collector and the left edge of the current collector. B1 The range is 2mm to 30mm, and the distance W between the right edge and the right edge of the current collector is... B2 The range is 3mm to 30mm; and W B1 -W A1 ≥1mm, W B2 -W A2 ≥1mm.

9. A method for preparing an electrode sheet as described in any one of claims 6-8, characterized in that, Including the following steps: The first adhesive is mixed with water and then applied to obtain an adhesive solution. The first conductive agent and inorganic filler are mixed evenly with the adhesive solution, or the first conductive agent, thermally stable active material and inorganic filler are mixed evenly with the adhesive solution to obtain a safety coating slurry. The safety coating slurry is applied to one or both sides of the current collector, or to the surface of the active material layer away from the current collector, to obtain the electrode sheet.

10. [Correction 27.12.2024 according to Rule 91] The method for preparing the electrode sheet according to claim 9 is characterized in that, Includes at least one of the following: C1) The mass ratio of the first conductive agent, the first binder, and the inorganic filler is (0.5~5):(1~21.2):(73.8~98.5); C2) The solid content of the adhesive solution is 10% to 30%; C3) The viscosity of the adhesive solution is 1×10 3 ~3×10 4 mPa·s; C4) The solid content of the safety coating slurry is ≥10%; C5) The viscosity of the safety coating slurry is ≥50 mPa·s; C6) The dyne value of the current collector is ≥30 dyn / cm; C7) The safety coating slurry is applied to one or both sides of the current collector surface, or the surface of the active material layer away from the current collector surface, by gravure printing. C8) When C7) is included, the oven temperature for gravure printing is 90-110℃ and the printing speed is 10-50m / min. C9) The mass ratio of the first conductive agent, the first binder, the inorganic filler, and the heat-stabilized active substance is (0.5~5):(1~21.2):(1~97.5):(1~97.5).

11. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode; the positive electrode and / or the negative electrode is an electrode sheet as described in any one of claims 6-8 or an electrode sheet obtained by the preparation method as described in any one of claims 9-10.

12. The application of the lithium-ion battery as described in claim 11 in an energy storage device, an electrical device, or an electronic device.

Images