Battery cell and preparation method therefor, and lithium-ion battery

Abstract

A battery cell and a preparation method therefor, and a lithium-ion battery, which relate to the technical field of secondary battery materials. In the provided battery cell, a safety coating is introduced into a positive electrode sheet, and the capacity contributed by a first active material in the safety coating is defined. The first active material not only reduces the possibility of contact between a positive electrode and a negative electrode and improves the mechanical safety performance of the battery cell, but also contributes a certain capacity, such that the N / P ratio (the ratio of a negative electrode capacity to a positive electrode capacity) of the battery cell is reduced, the potential of the positive electrode at a fully charged state is lowered, and the thermal abuse performance and cycling performance of the battery are improved. Finally, by means of defining relevant parameters, a battery cell, which has mechanical safety performance, hot box performance and cycling performance, and can improve the low-temperature discharge performance and the rate discharge performance, is provided without changing an original process.

Description

A battery cell and its preparation method, a lithium-ion battery Technical Field

[0001] This invention relates to the field of secondary battery materials technology, and in particular to a battery cell and its preparation method, and a lithium-ion battery. 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 mechanical safety tests such as needle penetration and thermal abuse safety tests such as hot box tests for lithium batteries are becoming increasingly stringent. To improve the mechanical safety performance of battery cells, the industry mostly adopts the method of coating a safety coating on the positive electrode current collector. This safety coating typically contains a certain proportion of inorganic fillers, conductive agents, and binders. However, conventional safety coatings are not very effective in improving the thermal abuse safety performance of battery cells. To further improve the thermal abuse safety performance of battery cells, most methods involve doping and coating the positive and negative electrode active materials, or developing electrolytes with high thermal stability. However, these methods suffer from drawbacks such as long development cycles and high development costs.

[0004] Therefore, it is of great significance to address the problem that current conventional improvement measures cannot simultaneously and effectively improve the mechanical safety performance and thermal abuse safety performance of battery cells, and to provide a battery cell that can take into account mechanical safety performance, thermal box performance and cycle performance without changing the original process, while improving low temperature discharge performance and rate discharge 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 battery cell and its preparation method, as well as a lithium-ion battery, aiming to address the problem that current conventional improvement measures cannot simultaneously and effectively improve the mechanical safety performance and thermal abuse safety performance of the battery cell.

[0006] In a first aspect, the present invention provides a battery cell comprising: a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprising a safety coating and a positive active material layer, the safety coating comprising a first active material and a dispersant, the positive active material layer comprising a positive active material; the negative electrode sheet comprising a negative active material layer, the negative active material layer comprising a negative active material.

[0007] The first capacity ratio NP1 of the battery cell satisfies 1.019≤NP1≤1.089, and the relative capacity ratio ΔNP satisfies 0.002≤ΔNP≤0.04;

[0008] The formula for calculating the first capacity ratio NP1 is: NP1=C0 / C2-ΔNP, and the formula for calculating the relative capacity ratio ΔNP is: ΔNP=C0×C1 / (C2×(C1+C2))-0.05;

[0009] C1 is the capacity of the first active substance in a unit area of ​​the safety coating. The formula for calculating C1 is: C1 = k × c w ×a, 0<k<1, 0<a≤300, c w denoted as the areal density of the single-sided coating of the safety coating, a is the theoretical specific capacity of the first active material, and k is a constant;

[0010] C2 represents the capacity exerted by the positive electrode active material per unit area of ​​the positive electrode active material layer;

[0011] C0 represents the capacity exerted by the negative electrode active material per unit area of ​​the negative electrode active material layer.

[0012] The battery cell according to the embodiments of the present invention has at least the following beneficial effects: The battery cell provided by the present invention introduces a safety coating in the positive electrode and limits the capacity of the first active material in the safety coating. It can take into account the mechanical safety performance, thermal performance and cycle performance of the battery cell without changing the original process, and improve the low temperature discharge performance and rate discharge performance.

[0013] In this invention, C1 is defined as the capacity of the first active substance in a unit area of ​​the safety coating, and the formula for calculating C1 is: C1 = k × c w ×a, 0<k<1, 0<a≤300, c wLet 'a' be the single-sided coating density of the safety coating, 'a' be the theoretical specific capacity of the first active material, and 'k' be a constant related to the cell system and depth of discharge. Generally, the larger 'a' is, the worse the stability of the active material. This invention limits it to 0 < a ≤ 300. At this value, the first active material has good thermal stability, is less prone to structural collapse or deformation, and is less likely to decompose during mechanical abuse tests such as needle penetration, reducing the risk of thermal runaway and improving battery safety. Furthermore, the first active material not only reduces the possibility of contact between the positive and negative electrodes, improving the mechanical safety performance of the cell, but also provides a certain capacity, thereby reducing the N / P ratio (the ratio of negative electrode capacity to positive electrode capacity), lowering the potential of the positive electrode at full charge, and improving the battery's thermal abuse and cycle performance. Let C2 be the capacity provided by the positive active material per unit area of ​​the positive active material layer, and C0 be the capacity provided by the negative active material per unit area of ​​the negative active material layer. This invention defines the ratio of C0 to C2 as the N / P ratio (the ratio of negative electrode capacity to positive electrode capacity, N / P ratio = C0 / C2). The change in NP value due to the introduction of the safety coating is defined as ΔNP (relative capacity ratio). The formula for calculating ΔNP is: ΔNP = C0 × C1 / (C2 × (C1 + C2)) - 0.05. The corresponding cell capacity ratio is NP1, calculated as: NP1 = C0 / C2 - ΔNP. This invention limits the range of ΔNP to 0.002 to 0.04. When ΔNP is below 0.002, the corresponding C... w When the value is relatively small, processing becomes more difficult, the adjustment of the NP value is not significant, and the safety coating is thinner, which can negatively impact the mechanical safety performance of the battery cell. When ΔNP is greater than 0.04, the corresponding c... w A relatively large value for NP1 can negatively impact the energy density of the battery cell. This invention also limits the range of NP1 values. When NP1 is less than 1.019, it indicates that the capacity of the negative electrode is lower than that of the positive electrode, posing a risk of lithium plating in the cell. When the value is greater than 1.089, it indicates that the negative electrode has sufficient capacity, leading to greater irreversible lithium loss during formation, reducing the cell's initial efficiency. Simultaneously, the negative electrode is not fully utilized, resulting in a decrease in the cell's energy density. Furthermore, it deepens the charging depth of the positive electrode, increasing the potential of the fully charged positive electrode, thus deteriorating the cell's cycle performance and thermal performance. Considering the need to allow for a certain margin to cope with process fluctuations, this invention limits the range of NP1 values ​​to 1.019–1.089.

[0014] Ultimately, by limiting relevant parameters, this invention provides a battery cell with good mechanical safety performance, thermal performance, and cycle performance, while also improving low-temperature discharge performance and cycle performance.

[0015] In this invention, C1 represents the capacity exerted by the first active material per unit area of ​​the safety coating, C2 represents the capacity exerted by the positive active material per unit area of ​​the positive active material layer, and C0 represents the capacity exerted by the negative active material per unit area of ​​the negative active material layer. "Unit area" can refer to "per square meter," "per square centimeter," "per square millimeter," or other suitable units, as long as C1, C2, and C0 are in the same unit. Since the formula for calculating the relative capacity ratio ΔNP is: ΔNP = C0 × C1 / (C2 × (C1 + C2)) - 0.05, and the formula for calculating the first capacity ratio NP1 is: NP1 = C0 / C2 - ΔNP, it can be seen that the units of C1, C2, and C0 do not affect the value of ΔNP or NP1.

[0016] In some embodiments of the present invention, the first capacity ratio NP1 of the battery cell satisfies 1.028≤NP1≤1.053.

[0017] In some embodiments of the present invention, C1 is calculated as follows: C1 = k × c w ×a, 0<k<1, 0<a≤300, c w Here, 'a' represents the single-sided coating density of the safety coating, 'a' represents the theoretical specific capacity (constant) of the first active material, and 'k' is a constant related to the cell system and depth of discharge. Preferably, 100 ≤ a ≤ 200. When 'a' is greater than 200, the stability of the active material is poor; when 'a' is less than 100, reducing the N / P ratio by the same amount requires an additional increase in the amount of the first active material.

[0018] In some embodiments of the present invention, c w The value range is 3mg / 1540.25mm. 2 ~18mg / 1540.25mm 2 This invention discovers that when c w Less than 3mg / 1540.25mm 2 When c is present, it will not affect the NP value of the system, but the processing is more difficult, the safety coating is thinner, and it will also have an adverse effect on the mechanical safety performance of the battery cell; while when c w Above 18mg / 1540.25mm 2 At this point, there is no improvement in the safety performance of the battery cell (the pass rate of the battery cell needle penetration test has reached 100% below this value), and on the contrary, it will have an adverse effect on the energy density of the battery cell. Based on the above considerations, this invention c w The value range is 3mg / 1540.25mm. 2 ~18mg / 1540.25mm 2 .

[0019] In some embodiments of the present invention, the first active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, and ternary materials, preferably one or more of active materials with good thermal stability such as lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate. Active materials with good thermal stability have a very stable olivine-type crystal structure, which is not prone to structural collapse or deformation, and is also not prone to decomposition during mechanical abuse tests such as needle penetration, reducing the risk of thermal runaway and improving battery safety. Furthermore, the first active material can also provide a certain capacity, thereby reducing the N / P ratio (the ratio of negative electrode capacity to positive electrode capacity) of the battery cell, lowering the potential of the positive electrode when fully charged, and improving the battery's thermal abuse performance and cycle performance.

[0020] In some embodiments of the present invention, the median particle size D of the first active substance is... v50 The surface area ranges from 0.1 to 15 μm, and the specific surface area ranges from 2 to 50 m². 2 / g. Median particle size D of the first active substance. v50 Less than 0.1 μm, or with a specific surface area greater than 50 m² 2 / g, is highly prone to agglomeration during slurry mixing, while when D v50 Greater than 15 μm, or when the specific surface area is less than 2 m² 2 When the particle size is large, it is difficult to obtain a thin safety coating, which affects the energy density of the battery cell. Furthermore, during the application of the safety coating, it is easy for the base coat to be missed, which affects the safety of the battery cell.

[0021] In some embodiments of the present invention, the battery cell includes at least one of the following:

[0022] A1) The first active material is a ternary material, and the ternary material includes at least one of nickel-cobalt-manganese ternary material and nickel-cobalt-aluminum ternary material;

[0023] A2) When A1) is included, the nickel-cobalt-manganese ternary material includes at least one of NCM333, NCM523, NCM613, NCM622 and NCM811;

[0024] A3) The surface of the first active substance is coated with an inorganic ceramic material;

[0025] A4) When A3) is included, the inorganic ceramic material includes silicon dioxide, aluminum oxide or titanium oxide.

[0026] In some embodiments of the present invention, the ternary material includes at least one of nickel-cobalt-manganese ternary material (NCM) and nickel-cobalt-aluminum (NCA) ternary material. The ternary material used in the present invention can be any ternary material commonly used in the art, and no limitation is made herein. For example, the nickel-cobalt-manganese ternary material may include at least one of NCM333, NCM523, NCM613, NCM622, and NCM811.

[0027] In some embodiments of the present invention, the surface of the first active material is coated with an inorganic ceramic material.

[0028] In some embodiments of the present invention, the inorganic ceramic material includes silicon dioxide, aluminum oxide, or titanium oxide.

[0029] The first active material can be coated with an inorganic ceramic material such as silica, alumina, or titanium dioxide onto its particle surface. These ceramic materials can inhibit the migration of free lithium ions from the surface of the first active material into the solution, reduce the pH of the coating slurry, and decrease the corrosion of the current collector aluminum foil.

[0030] In some embodiments of the present invention, the dispersant includes one or more of ionic dispersants, nonionic dispersants, amphoteric dispersants, and fluorosurfactants.

[0031] In some embodiments of the present invention, the ionic dispersant includes one or more of polyacrylic acid and its salts, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and polyethyleneimine.

[0032] In some embodiments of the present invention, the nonionic dispersant includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, polyoxyethylene, and carboxymethyl cellulose.

[0033] In some embodiments of the present invention, the amphoteric dispersant includes betaine.

[0034] Because the primary active material is insoluble in water, has small particles, and a large specific surface area, it is prone to agglomeration during stirring and dispersion. Therefore, a dispersant must be added. Dispersants improve the dispersion of the poorly dispersed primary active material in the slurry. They can be one or more of the following: ionic dispersants, such as polyacrylic acid (PAA) and its salts, sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), and polyethyleneimine (PEI); nonionic dispersants, such as polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyoxyethylene (POE), and carboxymethyl cellulose (CMC); amphoteric dispersants, such as betaine; and fluorosurfactants. Dispersants reduce the mutual attraction between inorganic filler particles, thereby improving the dispersibility of the particles in the adhesive. Good dispersibility ensures uniform distribution of inorganic filler particles, reduces agglomeration, lowers slurry viscosity, improves coating uniformity, and helps improve the electrochemical performance of the battery cell. Preferably, the dispersant is selected from polyacrylic acid (PAA) and its salts, or polyvinylpyrrolidone (PVP).

[0035] In some embodiments of the present invention, the safety coating further includes a first conductive agent, a first binder, and an inorganic filler.

[0036] In some embodiments of the present invention, the safety coating satisfies at least one of the following:

[0037] B1) The mass ratio of the first conductive agent, the first binder, the inorganic filler, the first active substance, and the dispersant is (0.5~5):(1~21.2):(1~50):(1~95):(0.01~1);

[0038] B2) The median particle size D of the inorganic filler v50 The surface area ranges from 0.1 to 5 μm, and the specific surface area ranges from 8 to 15 m². 2 / g;

[0039] B3) The inorganic filler includes one or more of alumina, boehmite, aluminum hydroxide, magnesium hydroxide, silicon dioxide, or titanium dioxide;

[0040] B4) The first adhesive includes one or more of polyvinylidene fluoride adhesive, sodium carboxymethyl cellulose adhesive, or polyacrylate adhesive.

[0041] In some embodiments of the present invention, the mass ratio of the first conductive agent, the first binder, the inorganic filler, the first active substance, and the dispersant is (0.5–5):(1–21.2):(1–50):(1–95):(0.01–1). 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; the inorganic filler can be 1–50 parts; the first active substance can be 1–95 parts; and the dispersant can be 0.01–1 parts.

[0042] In some embodiments of the present invention, the median particle size D of the inorganic filler is... v50 The surface area ranges from 0.1 to 5 μm, and the specific surface area ranges from 8 to 15 m². 2 / g. When the D of inorganic filler v50 Smaller than 0.1 μm, but with a specific surface area greater than 15 m². 2 When 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 5μm, while specific surface area is less than 8m². 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.

[0043] In some embodiments of the present invention, the inorganic filler includes one or more of alumina, boehmite, aluminum hydroxide, magnesium hydroxide, silicon dioxide, or titanium dioxide. Boehmite is preferred because it is not only cheaper than other inorganic fillers, but also has a lower Rockwell hardness, resulting in less wear on the gravure roller and thus reducing manufacturing costs.

[0044] In some embodiments of the present invention, the mass fraction of inorganic filler in the safety coating is 1% to 50%.

[0045] 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.

[0046] 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.

[0047] In some embodiments of the present invention, the structural formula of the polyacrylate adhesive is as follows:

[0048] Each time R1 appears, it is independently selected from H, Li, or Na;

[0049] Each occurrence of R2 is independently selected from substituted or unsubstituted C1 to C2. 10 Alkyl groups;

[0050] And 5≤(x+z) / y≤20, 1.2≤z / x≤2, and x, y, and z are all not 0.

[0051] 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 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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%.

[0059] This invention achieves regulation of the electrolyte absorption rate of the binder by limiting the content of cyano groups, ester groups, 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.

[0060] 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.

[0061] 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.

[0062] 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, M is preferred w / M n The range is 1.5 to 1.9.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] In one specific embodiment, the present invention also provides a method for preparing the above-mentioned polyacrylate adhesive, comprising the steps of:

[0067] S1. Add dispersion medium to the reaction vessel and remove oxygen;

[0068] 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;

[0069] S3. Add an initiator and heat to initiate the reaction;

[0070] S4. After the reaction is complete, the product is filtered, dried, crushed and sieved to obtain a polyacrylate adhesive.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] In some embodiments of the present invention, the initiator includes 20% ammonium persulfate, but is not limited thereto.

[0076] 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.

[0077] 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.

[0078] In some embodiments of the present invention, the positive electrode sheet further includes a positive current collector, the safety coating is coated on at least one side surface of the positive current collector, and the positive active material layer is coated on the side surface of the safety coating away from the positive current collector and / or the side surface of the positive current collector away from the safety coating.

[0079] In some embodiments of the present invention, the negative electrode sheet further includes a negative electrode current collector, and the negative electrode active material layer is coated on at least one side surface of the negative electrode current collector.

[0080] The positive electrode sheet provided by the present invention has a safety coating 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: current collector 022; safety coating 023, disposed on at least one surface of the current collector 022; and positive electrode active material layer 011, disposed on the surface of the safety coating 023 away from the current collector 022.

[0081] 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.

[0082] In some embodiments of the present invention, the single-sided coating surface density of the safety coating is 3 mg / 1540.25 mm. 2 ~18mg / 1540.25mm 2 For example, it can be 3-6 mg / 1540.25 mm. 2 6-9 mg / 1540.25 mm 2 9-12 mg / 1540.25 mm 2 12-15mg / 1540.25mm 2 15-18mg / 1540.25mm 2 When below 3mg / 1540.25mm 2 While this won't affect the NP value of the system, it makes processing more difficult, and the thinner safety coating can negatively impact the mechanical safety performance of the battery cell; and while values ​​above 18mg / 1540.25mm... 2 At this point, there is no improvement in the safety performance of the battery cell (the pass rate of the battery cell needle penetration test has reached 100% below this value), and on the contrary, it will have an adverse effect on the energy density of the battery cell. Based on the above considerations, the single-sided coating surface density of the safety coating of this invention is 3mg / 1540.25mm². 2 ~18mg / 1540.25mm 2 .

[0083] In some embodiments of the present invention, the safety coating is applied to both surfaces of the current collector. The safety coating satisfies at least one of the following:

[0084] C1) The thickness of the safety coating on both sides is 1–20 μm;

[0085] C2) The double-sided diaphragm resistance of the safety coating tested under 0.4t pressure is 0.5~5Ω;

[0086] C3) The double-sided thickness d of the safety coating and the value of the double-sided diaphragm resistance R under 0.4t pressure satisfy the condition: 2≤R×d≤50;

[0087] C4) Along the unwinding direction perpendicular to the positive electrode current collector, the distance W between the left edge of the safety coating on side A of the positive electrode current collector and the left edge of the positive electrode current collector. A1 The range is 2mm to 30mm, and the distance W between the right edge and the right edge of the positive 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 positive electrode current collector and the left edge of the positive electrode current collector. B1 The range is 3mm to 30mm, and the distance W between the right edge and the right edge of the positive current collector is... B2 The range is 3mm to 30mm; and W B1 -W A1 ≥1mm, W B2 -W A2 ≥1mm.

[0088] In some embodiments of the present invention, the double-sided thickness d (i.e., the sum of the thicknesses of the safety coatings applied to both sides of the current collector surface) 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.

[0089] 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 0.5–5Ω, for example, it can be 0.5–2Ω, 2–3.5Ω, or 3.5–5Ω. 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 0.5–5Ω@0.4t can balance both safety performance and cycle performance.

[0090] 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.

[0091] 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.

[0092] In some embodiments of the present invention, the raw materials of the positive electrode active material layer include a positive electrode active material, a second conductive agent, and a second binder.

[0093] In some embodiments of the present invention, the positive electrode active material accounts for 90% to 98% of the mass percentage of the positive electrode active material layer.

[0094] 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.

[0095] In some embodiments of the present invention, the second conductive agent accounts for 0.5% to 5% of the mass percentage of the positive electrode active material layer, preferably 0.5% to 2%. If the content of the second conductive agent is too low, the cycle performance of the 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 cell safety performance.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] In some embodiments of the present invention, the positive electrode sheet further includes a positive current collector. The positive current collector is not limited and can be a common positive current collector, such as aluminum foil or composite aluminum foil.

[0101] In some embodiments of the present invention, the dyne value of the positive current collector is not less than 30 dyn / cm, preferably not less than 38 dyn / cm. When the dyne value of the current collector is less than 30 dyn / cm, 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. When the dyne value of the current collector is not less than 38 dyn / cm, it can ensure that the primer has a good appearance and that the adhesion between the safety coating and the current collector is good.

[0102] In some embodiments of the present invention, the raw materials of the negative electrode active material layer include a negative electrode active material, a third conductive agent, and a third binder.

[0103] In some embodiments of the present invention, the negative electrode active material accounts for 90% to 98% of the mass percentage of the negative electrode active material layer.

[0104] 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 negative electrode active material layer.

[0105] In some embodiments of the present invention, the third conductive agent accounts for 0.5% to 5% of the mass percentage of the negative electrode active material layer, preferably 0.5% to 2%. If the content of the third conductive agent is too low, the cycle performance of the 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 cell safety performance.

[0106] In some embodiments of the present invention, the third conductive agent includes at least one selected from acetylene black, graphene, graphyne, carbon nanotubes, carbon fibers, and conductive carbon black. The present invention does not have special requirements for the third 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.

[0107] In some embodiments of the present invention, the third binder accounts for 0.5% to 5% of the mass percentage of the negative electrode active material layer. If the amount of the third binder 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 third binder is too large, it will make the active material layer difficult to process and will also worsen the internal resistance of the cell.

[0108] In some embodiments of the present invention, the third adhesive includes at least one selected from 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 third adhesive; conventional adhesives in the art can be used.

[0109] In some embodiments of the present invention, the negative electrode sheet further includes a negative electrode current collector. The negative electrode current collector is not limited and can be a common negative electrode current collector, such as copper foil or composite copper foil.

[0110] In some embodiments of the present invention, the dyne value of the negative electrode current collector is not less than 30 dyn / cm, preferably not less than 38 dyn / cm. When the dyne value of the current collector is less than 30 dyn / cm, 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. When the dyne value of the current collector is not less than 38 dyn / cm, it can ensure that the primer has a good appearance and that the adhesion between the safety coating and the current collector is good.

[0111] In some embodiments of the present invention, the battery cell further includes a separator spaced between the positive electrode and the negative electrode.

[0112] A second aspect of the present invention provides a method for preparing the above-mentioned battery cell, comprising the steps of:

[0113] S100. Mix the raw materials for preparing the safety coating evenly in a solvent to obtain a safety coating slurry;

[0114] S200: The safety coating slurry is coated onto at least one side surface of the positive electrode current collector to obtain a positive electrode current collector containing a safety coating;

[0115] S300: A positive electrode active material layer is coated on the surface of the safety coating away from the positive electrode current collector or on the surface of the positive electrode current collector away from the safety coating to obtain a positive electrode sheet;

[0116] S400. A negative electrode active material layer is coated on the negative electrode current collector to obtain a negative electrode sheet.

[0117] S500: Assemble the positive and negative electrode plates to obtain a battery cell.

[0118] The method for preparing a battery cell according to embodiments of the present invention has at least the following beneficial effects: By introducing a safety coating into the positive electrode and limiting the capacity of the active material in the safety coating, the present invention can balance the mechanical safety performance, thermal performance, and cycle performance of the battery cell, while improving low-temperature discharge performance and rate discharge performance, 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.

[0119] In some embodiments of the present invention, the safety coating includes at least one of the following:

[0120] D1) The solid content of the safety coating slurry is ≥10%;

[0121] D2) The viscosity of the safety coating slurry is ≥50 mPa·s;

[0122] D3) The dyne value of the positive current collector is ≥30 dyn / cm;

[0123] D4) The safety coating slurry is applied to one or both surfaces of the positive electrode current collector by gravure printing;

[0124] D5) When D4) is included, the oven temperature for gravure printing is 90-110℃ and the printing speed is 10-50m / min.

[0125] In some embodiments of the present invention, the raw materials of the safety coating include a first conductive agent, a first binder, an inorganic filler, a first active substance, a dispersant, and a cosolvent.

[0126] In some embodiments of the present invention, the mass ratio of the first conductive agent, the first binder, the inorganic filler, the first active substance, the dispersant, and the co-solvent is (0.5–5):(1–21.2):(1–50):(1–95):(0.01–1):(1–20). 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; the inorganic filler can be 1–50 parts; the first active substance can be 1–95 parts; the dispersant can be 0.01–1 part; and the co-solvent can be 1–20 parts.

[0127] In some embodiments of the present invention, the co-solvent includes one or more of isopropanol, ethanol, ethylene glycol, acetone, and ethyl acetate. The co-solvent can optimize the slurry performance and can be one or more of isopropanol (IPA), ethanol, ethylene glycol, acetone, and ethyl acetate. The co-solvent can reduce the viscosity of the slurry, improve the wettability of the slurry to the current collector, ensure that the slurry can uniformly cover the surface of the current collector, and form a more uniform and dense safety coating, thereby improving the coating quality. Furthermore, during the production of the safety coating, the evaporation rate of the co-solvent is generally faster than that of the main solvent, which helps to quickly form a uniform coating and reduce coating defects. Preferably, the co-solvent is selected from isopropanol (IPA), a commonly used co-solvent with good solubility and volatility, which can effectively improve the performance of the slurry.

[0128] In some embodiments of the present invention, the solid content of the safety coating slurry is ≥10%, preferably 10% to 21%.

[0129] In some embodiments of the present invention, the viscosity of the safety coating slurry is ≥50 mPa·s.

[0130] 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.

[0131] In some embodiments of the present invention, the dyne value of the positive electrode current collector and / or the negative electrode current collector is ≥30 dyn / cm, preferably ≥38 dyn / cm. When the dyne value of the current collector is less than 30 dyn / cm, 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.

[0132] In some embodiments of the present invention, the safety coating slurry is applied to one or both surfaces of the positive current collector by gravure printing.

[0133] 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.

[0134] 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 can lead to incomplete application of the safety coating, negatively impacting the safety performance of the battery cell.

[0135] In some embodiments of the present invention, the method for preparing the positive electrode includes the following steps:

[0136] (10) The first adhesive is mixed with the solvent and then applied to obtain the adhesive solution;

[0137] (20) The adhesive, the first conductive agent, the inorganic filler, the first active substance, the dispersant, and the co-solvent are mixed evenly to obtain a safety coating slurry;

[0138] (30) The safety coating slurry obtained in step (20) 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.

[0139] 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.

[0140] In some embodiments of the present invention, the first adhesive is a polyacrylate adhesive.

[0141] 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%.

[0142] 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.

[0143] 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 safety coating; while if the solid content and viscosity are too high, it may lead to difficulties in processing the safety coating.

[0144] In some embodiments of the present invention, the total length of the positive current collector 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.

[0145] In some embodiments of the present invention, a safety coating can be applied to both sides (surface A and surface B) of the positive current collector, 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 .

[0146] In some preferred embodiments of the present invention, to improve production efficiency and reduce costs, a ceramic layer may be applied only to the non-safety coating area on side B, while a safety coating may also be applied to the non-safety coating area on side A, i.e., a single-sided continuous coating structure may be provided. A2 It is 0, that is, L B1 +L B2 =L B =L A1 =L A =L.

[0147] 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 current collector with safety coating; 021 - reserved slot; 022 - current collector; 023 - safety coating; 024 - non-safety coating area. The safety coating area and the 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 with 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 LB1 +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).

[0148] 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 current collector, where N1 ≥ 0.

[0149] In some embodiments of the present invention, when applying the safety coating, N2 slots for electrode tab welding should be reserved in the safety coating area or non-safety coating area perpendicular to the unwinding direction of the current collector, where N2 ≥ 0.

[0150] 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 current collector, where N3 ≥ 1.

[0151] 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.

[0152] 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 tab welding must be kept so that the slots on the A / B sides are opposite each other, and the misalignment ΔW in the lateral and longitudinal directions does not exceed 2mm.

[0153] In some embodiments of the present invention, the safety coating is applied to both sides of the positive current collector, and along the unwinding direction perpendicular to the positive current collector, the distance W between the left edge of the safety coating on side A of the positive current collector and the left edge of the positive current collector is... A1 The range is 2mm to 30mm, and the distance W between the right edge and the right edge of the positive 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 positive electrode current collector and the left edge of the positive electrode current collector. B1 The range is 3mm to 30mm, and the distance W between the right edge and the right edge of the positive current collector is... B2 The range is 3mm to 30mm; and W B1 -W A1 ≥1mm, W B2 -W A2≥1mm. That is, if both sides of the positive current collector are coated with a safety coating, then along the unwinding direction perpendicular to the positive 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; 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.

[0154] In a third aspect, the present invention provides a lithium-ion battery comprising a cell as described above or a cell prepared by the method described above.

[0155] Since the lithium-ion battery adopts all the technical solutions of the cell in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments. That is, by introducing a safety coating into the electrode sheet and limiting the capacity of the first active material in the safety coating, the lithium-ion battery can balance the mechanical safety performance, thermal performance, and cycle performance of the cell, and improve the low-temperature discharge performance and rate discharge performance without changing the original process.

[0156] In some embodiments of the present invention, the battery cell includes: a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode.

[0157] 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-dN 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.

[0158] 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.

[0159] 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.

[0160] In some embodiments of the present invention, the lithium-ion 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.

[0161] This invention also proposes a secondary battery, comprising a cell as described above or a cell prepared by the method described above. The cell proposed in this invention can be applied not only to the aforementioned lithium-ion batteries, but also to other secondary batteries, including sodium-ion batteries, potassium-ion batteries, etc., without any limitations.

[0162] In a fourth 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

[0163] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0164] 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-positive electrode active material layer; 022-current collector; 023-safety coating;

[0165] 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;

[0166] Figure 3 is a top view of the current collector (unstripped state) containing a safety coating provided by the present invention;

[0167] 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

[0168] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] Example 1

[0173] This embodiment provides a lithium-ion battery, the positive electrode of which contains a safety coating. The safety coating includes a first active material lithium iron phosphate (LFP), a first binder, a first conductive agent Super P Li, and an inorganic filler boehmite.

[0174] The structural formula of the first adhesive is:

[0175] (1) Preparation of the first adhesive:

[0176] 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.

[0177] b) Then add 5 parts by weight of 20% ammonium persulfate solution as an initiator to initiate the reaction, and react for 5 hours;

[0178] 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 3.5×10 5 Number average molecular weight M w 1.8×10 5 M w / M n =1.94, electrolyte absorption rate c = 23%.

[0179] (2) Preparation of positive electrode current collector with safety coating:

[0180] 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 2.0 × 10⁻⁶ are obtained. 4 A gel solution of mPa·s was then added; subsequently, 58 parts of the first active material, lithium iron phosphate (median particle size D), were added. v50 Its diameter is 0.9 μm, and its specific surface area is 10.9 m². 2 / g), 30 parts of inorganic filler boehmite (median particle size D) v50 Its thickness is 0.4 μm, and its specific surface area is 9.5 m². 2 The following ingredients were mixed uniformly: 1.8 parts of the first conductive agent Super P Li, 0.2 parts of the dispersant polyvinylpyrrolidone (PVP), and 10% of the total weight of the slurry co-solvent isopropanol (IPA) to obtain a safety coating slurry with a solid content of 28% and a viscosity of 50–400 mPa·s. The safety coating slurry was then coated onto both sides of an aluminum foil using gravure printing. During coating, L... A2Set to 0, that is, L A1 =L A =L, N1=N3=1, N2=4. Safety coating surface density c (single-sided coating density). w It is 9mg / 1540.25mm 2 In addition, the oven temperature needs to be set to 95℃ and the printing speed to 30m / min during printing. The final double-sided coating surface density is 18mg / 1540.25mm. 2 A primer with a double-sided thickness of 10μm, a double-sided film resistance of 1.1Ω@0.4T, and an adhesion strength of 225N / m between the safety coating and the current collector. The capacity exerted by lithium iron phosphate per square meter of safety coating is C1=k×c w ×a, k is 0.306, a is 170, c w It is 9mg / 1540.25mm 2 Therefore, C1 is 468mAh.

[0181] (3) Preparation of positive electrode sheet:

[0182] A positive electrode slurry with a solid content of 75% and a viscosity of 7000 mPa·s was prepared by uniformly mixing lithium cobalt oxide (the positive electrode active material), a second 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 was then coated onto one side of the current collector aluminum foil containing the safety coating, with a coating areal density of 214 mg / 1540.25 mm². 2 After drying and winding at 85°C, the positive electrode slurry is coated and dried on the other side of the current collector aluminum foil containing the safety coating in the same way as described above. Then, the positive electrode sheet coated with positive electrode active material layer on both sides is cold-pressed. After that, it is cut and slit to make lithium-ion battery positive electrode sheet. The capacity C2 of lithium cobalt oxide in each square meter of positive electrode sheet is 24409mAh.

[0183] (4) Preparation of negative electrode sheet:

[0184] Using water as a solvent, graphite, thickener, and SBR binder were mixed uniformly 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. This slurry was then coated onto one side of a copper current collector foil, with a coating surface density of 115 mg / 1540.25 mm². 2 The copper foil is dried and rolled up at 80°C. Then, the negative electrode slurry is coated and dried on the other side of the copper foil according to the above method to obtain a negative electrode sheet with active material coated on both sides. The capacity C0 of graphite in the negative electrode sheet per square meter is 25750mAh.

[0185] (5) Preparation of electrolyte:

[0186] 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.

[0187] (6) Battery fabrication:

[0188] 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.

[0189] Example 2

[0190] The difference from Example 1 is that the areal density of the positive electrode slurry coating during positive electrode preparation is 218 mg / 1540.25 mm. 2 The capacity C2 of lithium cobalt oxide per square meter of positive electrode is 24865mAh.

[0191] The rest is the same as in Example 1, and will not be repeated here.

[0192] Example 3

[0193] The difference from Example 1 is that the areal density of the positive electrode slurry coating during positive electrode preparation is 208.5 mg / 1540.25 mm. 2 The capacity C2 of lithium cobalt oxide per square meter of positive electrode is 23781mAh.

[0194] The rest is the same as in Example 1, and will not be repeated here.

[0195] Example 4

[0196] The difference from Example 1 is that during the preparation of the positive electrode, the surface density c of the safety coating on one side is increased. w It is 18mg / 1540.25mm 2 The capacity (C1) of lithium iron phosphate per square meter of safety coating is 936 mAh; the areal density of the positive electrode slurry coating is 200 mg / 1540.25 mm². 2 The capacity C2 of lithium cobalt oxide per square meter of positive electrode is 22812mAh.

[0197] The rest is the same as in Example 1, and will not be repeated here.

[0198] Example 5

[0199] The difference from Example 1 is that during the preparation of the positive electrode, the surface density c of the safety coating on one side is increased. w 3mg / 1540.25mm 2 The capacity (C1) of lithium iron phosphate per square meter of safety coating is 156 mAh.

[0200] The rest is the same as in Example 1, and will not be repeated here.

[0201] Example 6

[0202] The difference from Example 1 is that during the preparation of the positive electrode, the surface density c of the safety coating on one side is increased. w It is 6mg / 1540.25mm 2 The capacity (C1) of lithium iron phosphate per square meter of safety coating is 312 mAh.

[0203] The rest is the same as in Example 1, and will not be repeated here.

[0204] Example 7

[0205] The difference from Example 1 is that during the preparation of the positive electrode, the surface density c of the safety coating on one side is increased. w It is 12mg / 1540.25mm 2 The capacity (C1) of lithium iron phosphate per square meter of safety coating is 624 mAh.

[0206] The rest is the same as in Example 1, and will not be repeated here.

[0207] Example 8

[0208] The difference from Example 1 is that during the preparation of the positive electrode, the surface density c of the safety coating on one side is increased. w It is 18mg / 1540.25mm 2 The capacity (C1) of lithium iron phosphate per square meter of safety coating is 936 mAh.

[0209] The rest is the same as in Example 1, and will not be repeated here.

[0210] Example 9

[0211] The difference from Example 1 is that the first active material is replaced by lithium iron phosphate (LFP) with lithium manganese iron phosphate (LMFP), while the rest remains unchanged. The capacity of lithium manganese iron phosphate per square meter of safety coating is C1 = k × c. w ×a, k is 0.306, a is 170, c w It is 9mg / 1540.25mm 2 Therefore, C1 is 468mAh.

[0212] The rest is the same as in Example 1, and will not be repeated here.

[0213] Example 10

[0214] The difference from Example 1 is that the first active material is replaced by lithium iron phosphate (LFP) with lithium cobalt oxide (LCO), while the rest remains unchanged. The capacity of lithium cobalt oxide per square meter of safety coating is C1 = k × c. w ×a, k is 0.399, a is 274, c w It is 9mg / 1540.25mm 2 Therefore, C1 is 984mAh.

[0215] The rest is the same as in Example 1, and will not be repeated here.

[0216] Example 11

[0217] The difference from Example 1 is that the proportion of -CN in the first adhesive is 55% (n1), 30% (n2) of -COOLi, and 15% (n3) of -COOCH3, with a weight-average molecular weight M. w 3.6×10 5 Number average molecular weight M w 2.1×10 5 M w / M n =1.7, electrolyte absorption rate c = 22%.

[0218] The rest is the same as in Example 1, and will not be repeated here.

[0219] Example 12

[0220] The difference from Example 1 is that the proportion of -CN in the first adhesive is 53% (n1), 37% (n2) of -COOLi, and 10% (n3) of -COOCH3, with a weight-average molecular weight M. w 3.4×10 5 Number average molecular weight M w 2.0×10 5 M w / M n =1.7, electrolyte absorption rate c =17%.

[0221] The rest is the same as in Example 1, and will not be repeated here.

[0222] Example 13

[0223] The difference from Example 1 is that the median particle size D of the first active material, lithium iron phosphate (LFP), is... v50 It is 2μm.

[0224] The rest is the same as in Example 1, and will not be repeated here.

[0225] Example 14

[0226] The difference from Example 1 is that the median particle size D of the first active material, lithium iron phosphate (LFP), is... v50 It is 15μm.

[0227] The rest is the same as in Example 1, and will not be repeated here.

[0228] Example 15

[0229] 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.

[0230] The rest is the same as in Example 1, and will not be repeated here.

[0231] Comparative Example 1

[0232] The difference from Example 1 is that during the preparation of the positive electrode, the surface density c of the safety coating on one side is increased. w 30mg / 1540.25mm 2 The capacity (C1) of lithium iron phosphate per square meter of safety coating is 1561 mAh; the areal density of the positive electrode slurry coating is 200 mg / 1540.25 mm². 2 The capacity C2 of lithium cobalt oxide per square meter of positive electrode is 22812mAh.

[0233] The rest is the same as in Example 1, and will not be repeated here.

[0234] Comparative Example 2

[0235] The difference from Example 1 is that during the preparation of the positive electrode, the surface density c of the safety coating on one side is increased. w It is 2.5mg / 1540.25mm 2 The capacity (C1) of lithium iron phosphate per square meter of safety coating is 130 mAh.

[0236] The rest is the same as in Example 1, and will not be repeated here.

[0237] Comparative Example 3

[0238] The difference from Example 1 is that during the preparation of the positive electrode, the surface density c of the safety coating on one side is increased. w It is 18mg / 1540.25mm 2 The capacity (C1) of lithium iron phosphate per square meter of safety coating is 936 mAh; the areal density of the positive electrode slurry coating is 218 mg / 1540.25 mm². 2The capacity C2 of lithium cobalt oxide per square meter of positive electrode is 24865mAh.

[0239] The rest is the same as in Example 1, and will not be repeated here.

[0240] Comparative Example 4

[0241] The difference from Example 1 is that the areal density of the positive electrode slurry coating during positive electrode preparation is 202.5 mg / 1540.25 mm. 2 The capacity C2 of lithium cobalt oxide per square meter of positive electrode is 23097mAh.

[0242] The rest is the same as in Example 1, and will not be repeated here.

[0243] Comparative Example 5

[0244] The difference from Example 1 is that the safety coating does not contain the first active material during the preparation of the positive electrode.

[0245] The rest is the same as in Example 1, and will not be repeated here.

[0246] Comparative Example 6

[0247] The difference from Example 1 is that the safety coating does not contain a dispersant during the preparation of the positive electrode.

[0248] The rest is the same as in Example 1, and will not be repeated here.

[0249] Comparative Example 7

[0250] The difference from Example 1 is that the surface of the positive current collector is not coated with a safety coating.

[0251] The rest is the same as in Example 1, and will not be repeated here.

[0252] Test case

[0253] To verify the effect of the safety coating introduced in this invention on the performance of the battery cell, the electrolyte absorption rate c of the first adhesive, as well as the battery cell's needle penetration, 132℃ / 136℃ hot box, low temperature discharge performance, rate performance and cycle performance were tested.

[0254] 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.

[0255] 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.

[0256] 132℃ / 136℃ Hot Box Test Method: At room temperature, discharge to 3V with a constant current of 0.2C and let stand for 5 minutes; charge to 4.45V with a constant current and constant voltage of 1.0C and a cutoff rate of 0.05C. Then, conduct a hot box test on the fully charged cell. During the test, the cell is suspended in the oven, and the oven temperature is increased to 132℃ or 136℃ at a rate of 5±2℃ / min and maintained for 60 minutes before stopping. During the test, the cell surface temperature, ambient temperature and voltage need to be monitored. The cell passes the test if it does not catch fire or explode.

[0257] 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.

[0258] 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.

[0259] 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.

[0260] The parameter settings for Examples 1-15 and Comparative Examples 1-7 are shown in Table 1 below:

[0261] Table 1

[0262] The test results of Examples 1-15 and Comparative Examples 1-7 are shown in Table 2 below:

[0263] Table 2

[0264] As can be seen from the comparison of parameter settings in Table 1-2 and cell test results, compared with Comparative Examples 1-7, the safety coating in Examples 1-15 satisfies 0.002≤ΔNP≤0.04 and 1.019≤NP1≤1.089, which corresponds to a significant improvement in the needle penetration performance of the cell. The needle penetration test pass rate increased from 0% to over 80%, the temperature chamber temperature was increased by 4°C, and the low-temperature discharge performance, rate discharge performance and cycle performance were also improved. The capacity retention rate after 800 cycles at 25°C is not less than 90%, the discharge capacity at -10°C is not less than 70%@3.4V, and the discharge capacity at 2.0C is not less than 70%@3.4V.

[0265] As can be seen from Comparative Example 1, although the performance of the battery cell did not deteriorate significantly compared to Example 1, its ΔNP was 0.067, c w 30mg / 1540.25mm 2 This will lead to a decrease in its energy density and poor practicality.

[0266] As shown in Comparative Example 2, ΔNP is only 0.001, corresponding to c w It is 2.5mg / 1540.25mm 2 The coating process requires high precision, and the needle-punching performance deteriorates.

[0267] As shown in Comparative Example 3, NP1 is only 1.003, which is insufficient for the negative electrode capacity. During the cycle, lithium plating is very likely to occur, which will cause the cell to fail due to cycle drop.

[0268] As shown in Comparative Example 4, NP1 has a potential of 1.098 and a high potential at full charge, indicating that its thermal box and cycle performance have deteriorated.

[0269] Comparative Examples 5-7 show that the absence of a first active substance or dispersant in the safety coating, or the absence of a safety coating altogether, leads to a deterioration in cell performance.

[0270] In summary, the safety coating provided by this invention contains a first active material. By limiting the coating density and capacity of the first active material, the mechanical safety performance, thermal abuse performance, and cycle performance of the battery cell are improved, while simultaneously enhancing the low-temperature discharge performance and rate discharge performance of the battery. The battery cell provided by this invention, with a safety coating satisfying 0.002≤ΔNP≤0.04 and 1.019≤NP1≤1.089, can achieve a needle penetration pass rate greater than 80%, a 4°C increase in temperature, a capacity retention rate of not less than 90% after 800 cycles at 25°C, a discharge capacity of not less than 70%@3.4V at -10°C, and a discharge capacity of not less than 70%@3.4V at 2.0C.

[0271] 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. An electric cell, characterized by, include: A positive electrode sheet and a negative electrode sheet; the positive electrode sheet includes a safety coating and a positive electrode active material layer, the safety coating includes a first active material and a dispersant, and the positive electrode active material layer includes a positive electrode active material; The negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material; The first capacity ratio NP1 of the battery cell satisfies 1.019≤NP1≤1.089, and the relative capacity ratio ΔNP satisfies 0.002≤ΔNP≤0.04; The formula for calculating the first capacity ratio NP1 is: NP1=C0 / C2-ΔNP, and the formula for calculating the relative capacity ratio ΔNP is: ΔNP=C0×C1 / (C2×(C1+C2))-0.05; C1 is the capacity of the first active substance in a unit area of ​​the safety coating. The formula for calculating C1 is: C1 = k × c w ×a, 0<k<1, 0<a≤300, c w denoted as the areal density of the single-sided coating of the safety coating, a is the theoretical specific capacity of the first active material, and k is a constant; C2 represents the capacity exerted by the positive electrode active material per unit area of ​​the positive electrode active material layer; C0 represents the capacity exerted by the negative electrode active material per unit area of ​​the negative electrode active material layer.

2. The electric cell of claim 1, wherein, The first active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, and ternary materials; and / or the median particle size D50 of the first active substance is in the range of 0.1 to 15 μm v50 in the range of 0.1 to 15 μm, and the specific surface area is in the range of 2 to 50 m 2 / g.

3. The electric cell of claim 2, wherein, Includes at least one of the following: A1) The first active material is a ternary material, and the ternary material includes at least one of nickel-cobalt-manganese ternary material and nickel-cobalt-aluminum ternary material; A2) When A1) is included, the nickel-cobalt-manganese ternary material includes at least one of NCM333, NCM523, NCM613, NCM622 and NCM811; A3) The surface of the first active substance is coated with an inorganic ceramic material; A4) When A3) is included, the inorganic ceramic material includes silicon dioxide, aluminum oxide or titanium oxide.

4. The electric cell of claim 1, wherein, The dispersant includes one or more of ionic dispersants, nonionic dispersants, amphoteric dispersants, and fluorosurfactants.

5. The electric cell of claim 4, wherein, The ionic dispersant includes one or more of polyacrylic acid and its salts, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and polyethyleneimine; And / or, the nonionic dispersant includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, polyoxyethylene, and carboxymethyl cellulose; And / or, the amphoteric dispersant includes betaine.

6. The electric cell of claim 1, wherein, The safety coating further includes a first conductive agent, a first binder, and an inorganic filler; the safety coating satisfies at least one of the following: B1) The mass ratio of the first conductive agent, the first binder, the inorganic filler, the first active substance, and the dispersant is (0.5~5):(1~21.2):(1~50):(1~95):(0.01~1); B2) the inorganic filler has a median particle size D v50 in the range of 0.1 to 5 μm and a specific surface area of 8 to 15 m 2 / g; B3) The inorganic filler includes one or more of alumina, boehmite, aluminum hydroxide, magnesium hydroxide, silicon dioxide, or titanium dioxide; B4) The first adhesive includes one or more of polyvinylidene fluoride adhesive, sodium carboxymethyl cellulose adhesive, or polyacrylate adhesive.

7. The electric cell of claim 6, wherein, The first adhesive is a polyacrylate adhesive, and a structural formula of the polyacrylate adhesive is: 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 Mw of the polyacrylate-based adhesive is in the range of 200,000 to 500,000 w and the number average molecular weight Mn is in the range of 100,000 to 400,000 n and the number average molecular weight Mn is in the range of 100,000 to 400,000 and / or the weight average molecular weight M w of the polyacrylate-based adhesive is in the range of 100,000 to 1,000,000 g / mol n and the number average molecular weight M w of the polyacrylate-based adhesive is in the range of 50,000 to 500,000 g / mol n ≤ 3; And / or, the polyacrylate adhesive has an electrolyte absorption rate of 10% to 50% at 80°C; And / or, the mass fraction of the polyacrylate binder in the safety coating is 1% to 21.2%.

8. The electric cell of claim 1, wherein, The positive electrode further includes a positive current collector, the safety coating is coated on at least one side surface of the positive current collector, and the positive active material layer is coated on the side surface of the safety coating away from the positive current collector or the side surface of the positive current collector away from the safety coating; the negative electrode further includes a negative current collector, and the negative active material layer is coated on at least one side surface of the negative current collector. and / or the single-side coating area density of the safety coating is 3 mg / 1540.25 mm 2 ~ 18 mg / 1540.25 mm 2 .

9. The electric cell of claim 8, wherein, The safety coating is applied to both surfaces of the positive electrode current collector; the safety coating satisfies at least one of the following: C1) The thickness of the safety coating on both sides is 1–20 μm; C2) The double-sided diaphragm resistance of the safety coating tested under 0.4t pressure is 0.5~5Ω; C3) The double-sided thickness d of the safety coating and the value of the double-sided diaphragm resistance R under 0.4t pressure satisfy the condition: 2≤R×d≤50; C4) Along the unwinding direction perpendicular to the positive electrode current collector, the distance W between the left edge of the safety coating on side A of the positive electrode current collector and the left edge of the positive electrode current collector. A1 The range is 2mm to 30mm, and the distance W between the right edge and the right edge of the positive 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 positive electrode current collector and the left edge of the positive electrode current collector. B1 The range is 3mm to 30mm, and the distance W between the right edge and the right edge of the positive current collector is... B2 The range is 3mm to 30mm; and W B1 -W A1 ≥1mm, W B2 -W A2 ≥1mm.

10. A method of producing an electric cell as claimed in any one of claims 1-9, characterized in that Including the following steps: The raw materials for preparing the safety coating are mixed evenly in a solvent to obtain a safety coating slurry; The safety coating slurry is applied to at least one side surface of the positive electrode current collector to obtain a positive electrode current collector with a safety coating. A positive electrode active material layer is coated on the surface of the safety coating away from the positive electrode current collector or on the surface of the positive electrode current collector away from the safety coating to obtain a positive electrode sheet; A negative electrode active material layer is coated onto the negative electrode current collector to obtain a negative electrode sheet; The positive and negative electrode plates are assembled to obtain a battery cell.

11. The method of claim 10, wherein the method further comprises, Includes at least one of the following: D1) The solid content of the safety coating slurry is ≥10%; D2) The viscosity of the safety coating slurry is ≥50 mPa·s; D3) The dyne value of the positive current collector is ≥30 dyn / cm; D4) The safety coating slurry is applied to one or both surfaces of the positive electrode current collector by gravure printing; D5) When D4) is included, the oven temperature for gravure printing is 90-110℃ and the printing speed is 10-50m / min.

12. A lithium-ion battery, characterized by, This includes the battery cell as described in any one of claims 1-9 or the battery cell obtained by the preparation method as described in any one of claims 10-11.

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

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