Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery. The battery comprises a positive plate, a diaphragm and an electrolyte, a coating of the diaphragm corresponds to a positive active layer of the positive plate, the coating comprises first particles and second particles, the first particles comprise one or more characteristic groups of a triazine ring, a pyrimidine ring and a phosphorus-oxygen double bond, the second particles comprise a polymer containing an ester group, and the electrolyte is a polymer containing an ester group. The second particles comprise primary particles, and in the 100 [mu] m * 100 [mu] m area of the first surface, far away from one side of the base material layer, in the coating, the number of the primary particles with the particle size smaller than or equal to 0.3 [mu] m accounts for 0.01%-4% of the number of the primary particles; the electrolyte comprises fluoroethylene carbonate, and the weight ratio of the fluoroethylene carbonate in the electrolyte is 13%-50%. According to the battery, the impedance of the CEI membrane can be reduced, the flexibility of the CEI membrane can be improved, and the cycling stability and the rate capability of the battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery. Background Art

[0002] With the widespread adoption of portable electronic devices and electric vehicles, lithium-ion batteries, as efficient energy storage solutions, have become a hot topic of research. However, as the number of charge and discharge cycles increases, the performance of the cathode active material gradually degrades, primarily manifesting as capacity fade and increased internal resistance. This not only impacts the battery's lifespan but also limits its further development in high-energy-density and high-power applications. Summary of the Invention

[0003] During the charge and discharge process of lithium-ion batteries, a solid electrolyte interface (CEI) film forms on the surface of the cathode active material. This film protects the cathode active material from electrolyte corrosion to a certain extent, and its performance has a crucial impact on the overall performance of the battery. Traditional CEI films often have some shortcomings, such as high impedance and poor mechanical properties. This can lead to significant polarization during battery cycling, which in turn accelerates battery performance degradation. Specifically, high-impedance CEI films increase the battery's internal resistance, reduce the battery's charge and discharge efficiency, and also lead to performance degradation at high charge and discharge rates. Meanwhile, CEI films with poor mechanical properties and lack of flexibility have difficulty adapting to the volume changes of the cathode active material during charge and discharge, which can easily lead to film rupture and continuous regeneration. This not only causes the CEI film to thicken and increase its impedance, but also increases interfacial side reactions, further exacerbating battery capacity degradation.

[0004] Therefore, in order to improve the cycle performance of the positive electrode active material, extend the service life of the battery, and improve its performance under high-rate charge and discharge conditions, it is urgent to optimize the CEI film on the surface of the positive electrode active material.

[0005] In light of this, the present invention provides a battery to address the high impedance and poor mechanical properties of conventional CEI membranes. This battery reduces the impedance and improves the flexibility of the CEI membrane, effectively lowering the battery's internal resistance and minimizing polarization. It also enhances the CEI membrane's protective effect on the positive electrode active material, enabling it to better adapt to the volume changes of the positive electrode material during charge and discharge, thereby significantly improving the battery's cycle stability and high-rate charge and discharge performance.

[0006] To achieve the above objectives, the present invention provides a battery, comprising a positive electrode sheet, a separator, and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on one or both surfaces of the positive electrode current collector, the separator comprises a substrate layer and a coating located on one or both surfaces of the substrate layer, the coating corresponding to the positive electrode active layer, the coating comprising first particles and second particles, the first particles comprising a first compound, the first compound comprising a characteristic group, the characteristic group comprising one or more of a triazine ring, a pyrimidine ring, and a phosphorus-oxygen double bond, the second particles comprising a first polymer, the first polymer being a polymer containing an ester group, the second particles comprising primary particles, the surface of the coating away from the substrate layer being the first surface, and within any 100 μm×100 μm area of ​​the first surface, the number of the primary particles having a particle size less than or equal to 0.3 μm accounts for 0.01%-4% of the total number of the primary particles; The electrolyte includes fluoroethylene carbonate, and the weight proportion of the fluoroethylene carbonate in the electrolyte is 13%-50%.

[0007] Through the above technical solution, the present invention has at least the following advantages compared with the prior art: The battery of the present invention can form an anion-derived interface rich in LiF and ester groups on the surface of the positive electrode sheet through the coordinated cooperation of the first particles and the second particles in the separator and the fluoroethylene carbonate in the electrolyte, so that the interface film on the surface of the positive electrode active material as a whole has low impedance and high flexibility, reducing the polarization phenomenon of the battery, reducing the cycle impedance of the battery, improving the cycle performance of the battery and improving the rate performance of the battery; at the same time, by controlling the number ratio of primary particles less than or equal to 0.3 μm in the primary particles of the second particles within an area of ​​100 μm×100 μm on the coating surface and the weight ratio of the fluoroethylene carbonate in the electrolyte, it can be ensured that the first particles dissolve an appropriate amount of substances containing electron-withdrawing groups and the second particles dissolve an appropriate amount of substances containing ester groups, thereby preventing the fluoroethylene carbonate in the electrolyte from excessively corroding the first and second particles.

[0008] Other features and advantages of the present invention will be described in detail in the following detailed description.

[0009] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Shown is one of the schematic cross-sectional views of the separator of the present invention.

[0011] Figure 2 Shown is the second cross-sectional schematic diagram of the diaphragm of the present invention.

[0012] Figure 3 Shown is a SEM image of the separator of the present invention. DETAILED DESCRIPTION

[0013] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention. In this article, unless otherwise specified, data ranges include endpoints.

[0014] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0015] The present invention provides a battery, comprising a positive electrode sheet, a separator, and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on one or both surfaces of the positive electrode current collector. The separator comprises a substrate layer and a coating located on one or both surfaces of the substrate layer, the coating corresponding to the positive electrode active layer. The coating comprises first particles and second particles. The first particles comprise a first compound, the first compound comprises a characteristic group, and the characteristic group comprises one or more of a triazine ring, a pyrimidine ring, and a phosphorus-oxygen double bond. The second particles comprise a first polymer, the first polymer being a polymer containing an ester group. The second particles comprise primary particles. The surface of the coating away from the substrate layer is the first surface. Within any 100 μm×100 μm area of ​​the first surface, the number of primary particles having a particle size of less than or equal to 0.3 μm accounts for 0.01% to 4% (for example, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%) of the total number of the primary particles. The electrolyte includes fluoroethylene carbonate, and the weight proportion of the fluoroethylene carbonate in the electrolyte is 13%-50% (for example, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48% or 50%).

[0016] like Figure 1 As shown, the diaphragm 1 includes a substrate layer 11 and a coating layer 12 located on one side of the substrate layer 11. In one embodiment, as shown in FIG. Figure 2As shown, the coating 12 can also be located on both sides of the substrate layer 11. In the present invention, when the coating is located on one side of the substrate layer, the positive electrode active layer corresponds to the coated side of the separator, and the negative electrode active layer corresponds to the other side of the separator; when the coating is located on both sides of the substrate layer, the positive electrode active layer corresponds to either coated side of the separator, and the negative electrode active layer corresponds to the other side of the separator.

[0017] In the present invention, the second particles may include primary particles. The percentage of primary particles having a particle size of less than or equal to 0.3 μm in the total number of primary particles within any 100 μm × 100 μm area on the surface of the coating refers to the percentage of single primary particles having a particle size of less than or equal to 0.3 μm in the total number of primary particles within any 100 μm × 100 μm area on the surface of the coating away from the carrier layer. Specifically, it can be tested by the following method: on the surface of the coating away from the carrier layer, arbitrarily select an area of ​​100μm×100μm containing the second particles. It should be understood that when the second particles (second coating) are discontinuously coated, an area of ​​100μm×100μm of the coating area should be selected. On the scanning image of the SEM, combined with graphic analysis software (for example, ImageJ, NanoMeasurer, Matlab, etc.), measurement and statistical processing are performed to obtain the particle size of all second particles, and the total number of primary particles in the second particles in the area is counted as M, wherein the number of single primary particles with a particle size of less than or equal to 0.3μm is N. Then, within the area of ​​100μm×100μm on the surface of the coating, the number of primary particles with a particle size of less than or equal to 0.3μm accounts for (N / M)×100% of the number of primary particles. Repeat the above operation 5 times, and take the average value as the final test result.

[0018] In the present invention, the characteristic group may include one or more of a triazine ring, a pyrimidine ring and a phosphorus-oxygen double bond. It is understood that the characteristic group is an electron-withdrawing group that can attract electron-carrying groups such as anions PF6-.

[0019] like Figure 3 As shown, the green circle is the first particle, and the red circle is the second particle. It can be understood that Figure 3 Only some of the first particles and some of the second particles are marked, and not all of the first particles and all of the second particles are marked.

[0020] The study found that a high content of fluoroethylene carbonate (FEC) in the electrolyte can slightly corrode the first and second particles in the diaphragm coating, causing the diaphragm coating surface to produce certain electron-withdrawing groups (i.e., characteristic groups, such as one or more of triazine rings, pyrimidine rings, and phosphorus-oxygen double bonds) and ester groups, thereby increasing the FEC and PF6 - and ester content, promoting anions (such as PF6 - ) Enter Li + The solvation layer forms an anion-derived interface rich in LiF and ester groups. The anion-derived interface rich in LiF and ester groups can reduce the impedance and flexibility of the interface film (including the CEI film) on the surface of the positive electrode active material as a whole, reduce the polarization phenomenon during the room temperature cycle of the battery, reduce the cycle impedance of the battery, improve the long cycle performance of the battery, and at the same time reduce the fast charging voltage drop, improve the charge and discharge performance of the battery at a large rate, and enhance the battery rate performance.

[0021] At the same time, in order to ensure the appropriate dissolution of the electron-withdrawing groups in the first particles and the ester groups in the second particles, and to prevent the fluoroethylene carbonate in the electrolyte from excessively corroding the first and second particles, the battery of the present invention simultaneously controls the proportion of primary particles less than or equal to 0.3 μm in the primary particles of the second particles per unit area of ​​the coating surface and the weight proportion of fluoroethylene carbonate in the electrolyte.

[0022] Primary particles with smaller particle sizes are more easily corroded by fluoroethylene carbonate. By controlling the proportion of primary particles with a particle size of 0.3 μm or less in the primary particles of the second particles per unit area of ​​the coating surface within the above range, it is possible to ensure that there are an appropriate amount of primary particles with smaller particle sizes in the coating, so that an appropriate amount of ester groups can be dissolved under the corrosion of fluoroethylene carbonate, thereby increasing the content of ester groups at the interface between the diaphragm and the positive electrode. At the same time, by controlling the weight proportion of fluoroethylene carbonate in the electrolyte within the above range, on the one hand, the ester groups in the first particles and the electron-withdrawing groups (characteristic groups) in the second particles can be dissolved in an appropriate amount, thereby avoiding excessive corrosion of the first and second particles by fluoroethylene carbonate, which affects the mechanical stability of the diaphragm. On the other hand, the FEC and PF6 at the interface between the diaphragm and the positive electrode can be improved. - and ester content, promoting anion PF6 - Enter Li +The solvent layer forms an anion-derived interface rich in LiF and ester groups, and fluoroethylene carbonate can form a CEI film rich in LiF and ester groups together with the ester group, reducing the impedance of the CEI film and improving the flexibility of the CEI film, so that the overall interface film on the surface of the positive electrode active material has low impedance and high flexibility, reducing the polarization phenomenon during the normal temperature cycle of the battery, reducing the cycle impedance of the battery, and improving the long cycle performance of the battery. At the same time, it reduces the fast charging voltage drop, improves the charge and discharge performance of the battery at a high rate, and improves the battery rate performance. In addition, the proportion of primary particles with a particle size of less than or equal to 0.3μm in the primary particles of the second particles per unit area of ​​the coating surface is controlled within the above range, which can also ensure that there are more primary particles with larger particle sizes in the coating. Primary particles with larger particle sizes are not easily corroded by fluoroethylene carbonate, which can ensure the overall structural stability of the second particles and avoid excessive dissolution of characteristic groups.

[0023] When the number of the primary particles with a particle size less than or equal to 0.3 μm accounts for less than 0.01% of the number of the primary particles in the area of ​​100 μm×100 μm of the first surface, the number of primary particles less than or equal to 0.3 μm in the primary particles of the second particles accounts for too low a proportion, and fluoroethylene carbonate is difficult to corrode the second particles with larger particle sizes, causing the ester groups to be difficult to dissolve or not dissolve. The content of ester groups at the interface between the diaphragm and the positive electrode is low, which is not conducive to the formation of a CEI film rich in LiF and ester groups. The impedance of the CEI is still high and the flexibility is poor, the capacity decay of the battery is aggravated, and the high-rate charge and discharge performance is poor. When the number of the primary particles with a particle size less than or equal to 0.3 μm accounts for more than 4% of the number of the primary particles within an area of ​​100 μm×100 μm of the first surface, the number of primary particles with a particle size less than or equal to 0.3 μm in the primary particles of the second particles accounts for too high a proportion, the degree of corrosion of the second particles by fluoroethylene carbonate is relatively large, which is not conducive to maintaining the overall structural stability of the second particles, the mechanical stability of the diaphragm is poor, and the interface stability between the diaphragm and the positive electrode is poor, which increases the interface impedance and reduces the cycle stability and rate performance of the battery.

[0024] When the weight proportion of the fluoroethylene carbonate in the electrolyte is less than 13%, the degree of corrosion of the first and second particles by the fluoroethylene carbonate is low, which is not conducive to the dissolution of characteristic groups and ester groups, and is not conducive to the formation of anion-derived interfaces. It is impossible to effectively reduce the impedance of the CEI membrane and improve the flexibility of the CEI membrane. The cycle stability of the battery is low, and the charge and discharge performance at high rates is reduced. When the weight proportion of the fluoroethylene carbonate in the electrolyte is greater than 50%, the degree of corrosion of the first and second particles by the fluoroethylene carbonate is too great, which is not conducive to maintaining the overall mechanical stability of the diaphragm. Delamination is likely to occur between the diaphragm and the battery, and the interface stability between the diaphragm and the positive electrode is poor, which increases the interface impedance and reduces the cycle stability and rate performance of the battery.

[0025] It can be understood that, in the present invention, the corrosion of the first particles and the second particles by fluoroethylene carbonate does not mean that the particle state of all the first particles and the second particles disappears or that all the first particles and the second particles are completely dissolved, but that the particle state of a single first particle and / or the particle state of a single second particle disappears completely or partially. It can also be that some groups in a single first particle and / or a single second particle are dissolved, and the particle state of a single first particle and a single second particle can still be retained.

[0026] In the present invention, the characteristic groups dissolved from the first particles and the ester groups dissolved from the second particles do not exist in the form of groups, but are substances carrying the groups, which can be one or more of small molecules, monomers, oligomers, and ions.

[0027] In the present invention, by simultaneously controlling the percentage of primary particles with a particle size of less than or equal to 0.3 μm within the second particle size per unit area of ​​the coating surface and the weight percentage of fluoroethylene carbonate in the electrolyte, the battery's cycle impedance is reduced, and its long-cycle performance and rate capability are improved compared to the prior art. To further enhance this effect, one or more of these technical features may be further optimized.

[0028] In one example, within an area of ​​100 μm×100 μm of the first surface, the number of the primary particles having a particle size less than or equal to 0.3 μm accounts for 1%-3.5% of the total number of the primary particles.

[0029] In one example, the first compound includes one or more of 2-phenylpyrimidine-4-carboxaldehyde, 1,4,6-dihydroxy-2-phenylpyrimidine, 5,6-diamino-2-phenyl-pyrimidine-4-ol, 4,6-dimethyl-2-phenylpyrimidine, uracil, cytosine, 2,4-dimercaptopyrimidine, 2,4-dimercapto-5,6-diaminopyrimidine, ammonium polyphosphate, diethylaluminum hypophosphite, melamine cyanurate, melamine thiocyanate, thiocyanic acid and 2,4,6-tris(4-hydroxyphenyl)-1,3,5-triazine.

[0030] In one example, the weight proportion A of the characteristic groups in the first surface is 20%-40% (eg, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38% or 40%).

[0031] In one example, the weight ratio A of the characteristic groups in the first surface is 25%-30%.

[0032] In one example, the weight percentage B of the ester groups in the first surface is 1%-20% (eg, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18% or 20%).

[0033] In one example, the weight ratio B of the ester groups in the first surface is 1.5%-15%.

[0034] In one example, the Dv10 of the first particles is 0.01 μm-0.5 μm (eg, 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, or 0.5 μm).

[0035] In one example, the first particles have a Dv98 of 2 μm to 5 μm (eg, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm).

[0036] In one embodiment, the Dv10 of the first particles is 0.01 μm-0.5 μm, and the Dv98 of the first particles is 2 μm-5 μm. Controlling the Dv10 and Dv98 of the first particles can further ensure that the fluoroethylene carbonate corrodes the first particles while avoiding excessive corrosion, ensuring that the corrosion does not affect the stability of the diaphragm structure, further reducing the impedance of the CEI membrane, reducing the polarization phenomenon of the battery during room temperature cycling, reducing the voltage drop of the battery during fast charging, and improving the battery's charge and discharge performance and rate performance.

[0037] In the present invention, Dv10 is the particle size corresponding to the 10% cumulative particle size distribution in the volume particle size distribution of the first particles. Dv98 is the particle size corresponding to the 98% cumulative particle size distribution in the volume particle size distribution of the first particles. In the present invention, the volume particle size distribution of the first particles can be obtained by arbitrarily selecting 100 μm × 100 μm in the SEM image of the coating surface, and combining it with graphic analysis software (for example, ImageJ, NanoMeasurer, Matlab, etc.) for measurement and statistical processing to obtain Dv10 and Dv98. The Dv10 of the first particles and the Dv98 of the first particles can also be obtained by testing with a laser particle size analyzer. For example, before preparing the diaphragm, the first particles are measured with a laser particle size analyzer to obtain the Dv10 of the first particles and the Dv98 of the first particles.

[0038] In one example, the first polymer includes an acrylic polymer.

[0039] In one example, the monomers forming the first polymer include one or more of methyl methacrylate, butyl acrylate, n-propyl acrylate, octyl acrylate, ethyl methacrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate.

[0040] In one example, the first polymer includes at least one of polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer (e.g., methyl methacrylate-acrylonitrile copolymer), acrylate-ethylene copolymer, acrylate-acrylonitrile-ethylene copolymer, styrene-acrylic ester monomer-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, and ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate.

[0041] In one example, the weight percentage of the ester-containing monomer in the first polymer is 50%-100% (eg, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%).

[0042] In one example, the glass transition temperature of the first polymer is 40°C to 75°C (eg, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, or 75°C).

[0043] In one embodiment, the second particles are arranged in a stacked manner in the coating. It is understood that stacked arrangement means that in the thickness direction of the diaphragm, the second particles are arranged in only one layer or multiple layers in the coating, and no large particle agglomerates are formed. Figure 3 As shown, the red circle is the second particle. It can be understood that Figure 3 Only some of the second particles are marked, not all of them.

[0044] In one embodiment, the Dv95 of the second particles is 0.5 μm-5 μm (for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm). In the present invention, Dv95 is the particle size corresponding to the 95% cumulative particle size distribution in the volume particle size distribution of the second particles. In the present invention, the volume particle size distribution of the second particles can be obtained by arbitrarily selecting 100 μm × 100 μm in the SEM image of the coating surface, and measuring and statistically processing the Dv95 using graphic analysis software (for example, ImageJ, NanoMeasurer, Matlab, etc.). The Dv95 of the second particles can also be obtained by testing with a laser particle size analyzer. For example, before preparing the diaphragm, the second particles are measured with a laser particle size analyzer to obtain the Dv95 of the second particles.

[0045] In one embodiment, the battery satisfies the following relationship: 1≤A / B≤30 (e.g., 1, 3, 5, 8, 10, 13, 15, 18, 20, 23, 25, 28, or 30), wherein A is the weight ratio of the characteristic groups in the first surface, and B is the weight ratio of the ester groups in the first surface. It is understood that A refers to the weight ratio of the characteristic groups in all elements exposed on the first surface, and B refers to the weight ratio of the ester groups in all elements exposed on the first surface. A and B can be changed by regulating one or more factors including the particle size of the first particles, the particle size of the second particles, the type of the first particles, the type of the second particles, the coverage of the second coating on the surface of the first coating, and the ratio of the first particles in the second coating.

[0046] In one example, the battery satisfies the following relationship: 3≤A / B≤18.

[0047] According to a specific embodiment, A is 20%-40%, B is 1%-20%, and the battery satisfies the following relationship: 1≤A / B≤30.

[0048] According to a specific embodiment, A is 25%-30%, B is 1.5%-15%, and the battery satisfies the following relationship: 3≤A / B≤18.

[0049] In one embodiment, the coating comprises a third particle, wherein the composition of the third particle comprises a fluoropolymer. Figure 3 As shown, the yellow circle is the third particle. It can be understood that Figure 3 Only some of the third particles are marked, not all of them.

[0050] In one example, the monomers forming the fluorine-containing polymer include one or more of vinylidene fluoride, tetrafluoroethylene, hexafluoroethylene, and hexafluoropropylene.

[0051] In one example, the fluorine-containing polymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, ethylene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0052] In one example, the third particles include primary particles and secondary particles.

[0053] In one example, the average particle size d1 of the secondary particles in the third particles is 2 μm-15 μm (eg, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm).

[0054] In one example, the average particle size d1 of the secondary particles in the third particles is 3 μm-10 μm.

[0055] In one example, the average particle size of the primary particles in the third particles is 0.15 μm to 0.4 μm (eg, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, or 0.4 μm).

[0056] In the present invention, the secondary particles of the third particles are formed by the aggregation of the primary particles of the third particles, wherein the agglomerates formed by the aggregation of more than 4 primary particles are secondary particles. The average particle size of the primary particles and the average particle size of the secondary particles in the third particles can be tested and obtained by the following method: taking the "average particle size of the secondary particles in the third particles" as an example, on the scanning image of the sample coating surface obtained by SEM, a square or rectangle with the smallest area that completely surrounds the secondary particles of one third particle is depicted, that is, a square or rectangle that depicts the edge of the secondary particles of the third particle and is connected to the four sides of the square or rectangle, and the length of one side of the square or the length of the long side of the rectangle is the particle size of the secondary particles of the third particle. In an arbitrarily selected 10μm*10μm area on the coating surface, the particle size of any 100 secondary particles of the third particles is measured, and the number average is the average particle size; repeat the above operation 5 times, and the average value is the average particle size of the secondary particles. It should be noted that, when 100 secondary particles can be observed in the captured image, the number average of the particle sizes of any 100 secondary particles in the image is set as the average particle size of the secondary particles. When 100 secondary particles are not observed in the image, multiple images are captured and the number average of the particle sizes of a total of 100 secondary particles is set as the average particle size. The scanned image can be obtained by observing the surface of the coating using a scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.). The average particle size of the primary particles in the third particles can be obtained by referring to the test method for the average particle size of the secondary particles in the third particles.

[0057] In one embodiment, the separator satisfies the following relationship: 1 ≤ d1 / d2 ≤ 25 (e.g., 1, 3, 5, 8, 10, 13, 15, 18, 20, 23, or 25), where d1 is the average particle size of the secondary particles in the third particles, in μm, and d2 is the Dv95 of the second particles, in μm. Controlling the separator to satisfy this relationship ensures that the coating does not excessively swell at room temperature, improves the mechanical stability of the coating at room temperature, reduces the impedance of the battery during long-term cycling at room temperature, and improves the battery's long-term cycling performance at room temperature.

[0058] In one example, the separator satisfies the following relationship: 1.5≤d1 / d2≤20.

[0059] According to a specific embodiment, d1 is 2-15, d2 is 0.5-5, and the diaphragm satisfies the following relationship: 1≤d1 / d2≤25.

[0060] According to a specific embodiment, d1 is 3-10, d2 is 0.5-5, and the diaphragm satisfies the following relationship: 1.5≤d1 / d2≤20.

[0061] In one example, the coating layer includes a first coating layer and a second coating layer, wherein the first coating layer is located between the substrate layer and the second coating layer, the first coating layer includes first particles, and the second coating layer includes second particles and optionally ("optionally" means that it may or may not be present) third particles.

[0062] In one example, the first coating layer has a thickness of 0.2 μm to 4 μm (eg, 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, or 4 μm).

[0063] In one example, the first coating layer includes an adhesive.

[0064] In one embodiment, the adhesive includes polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene acrylic latex, polyacrylonitrile, polyethyl acrylate, polyvinyl acetate, polyacrylate, polyurethane polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylic acid or one or more copolymer systems derived from the above polymers.

[0065] In one example, based on the total weight of the first coating layer, the weight of the first particles is 90%-99% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%), and the weight of the adhesive is 1%-10% (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%).

[0066] In one example, the second coating layer has a thickness of 0.5 μm to 5 μm (eg, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm).

[0067] In one example, the coverage of the second coating on the surface of the first coating is 15%-50% (eg, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%).

[0068] In the present invention, the coverage of the second coating on the surface of the first coating refers to the ratio of the area of ​​the second coating projected on the first coating to the surface area of ​​the first coating. The coverage of the second coating on the surface of the first coating can be measured by the following method: using SEM to obtain a microscopic image of the diaphragm surface, randomly dividing an area of ​​10000µm in the image, and then measuring the coverage of the second coating on the surface of the first coating. 2Take an area (for example, 100µm×100µm) and divide this area into uniform 100*100 squares. If the coverage area of ​​the orthographic projection of the second coating in the square exceeds half of the square area, it means that the square is occupied by the second coating; otherwise, it means that the square is not occupied by the second coating. Count the number of squares occupied by the second coating and record the total number of squares occupied by the second coating as X. The coverage rate = (X / 100*100)*100%. Repeat the above operation 5 times and take the average of the 5 times as the coverage rate of the second coating on the surface of the first coating.

[0069] In one example, based on the total weight of the second coating layer, the weight proportion of the second particles is 10%-100% (for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%), and the weight proportion of the third particles is 0%-90%.

[0070] According to a specific embodiment, Figure 2 As shown, the diaphragm 1 includes a substrate layer 11 and a coating layer 12, wherein the coating layer 12 is located on both sides of the substrate layer 11. The coating layer includes a first coating layer and a second coating layer, wherein the first coating layer is located between the substrate layer and the second coating layer.

[0071] In one example, Figure 1 As shown, when the coating layer 12 is located on one side of the substrate layer 11 , the diaphragm 1 further includes a third coating layer 13 , and the third coating layer 13 is located on the other side of the substrate layer 11 .

[0072] In one example, the diaphragm includes a substrate layer, a coating layer, and a third coating layer, wherein the coating layer is located on one surface of the substrate layer, and the third coating layer is located on the other surface of the substrate layer.

[0073] In one example, the coverage of the third coating on the surface of the substrate layer is 10%-50% (e.g., 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%). The coverage of the third coating on the surface of the substrate layer can be tested by referring to the test method for the coverage of the second coating on the surface of the first coating.

[0074] In one example, the third coating layer includes fourth particles, the fourth particles are arranged in a stacked manner in the third coating layer, and the fourth particles are composed of a second polymer, wherein the second polymer includes a polymer containing an ester group.

[0075] In the present invention, the fourth particles are arranged in layers in the third coating layer, which means that in the thickness direction of the diaphragm, the fourth particles are only one layer or multiple layers in the third coating layer, and no large-particle agglomerates appear.

[0076] In one example, the second polymer includes an acrylic polymer.

[0077] In one example, the monomers forming the second polymer include one or more of methyl methacrylate, butyl acrylate, n-propyl acrylate, octyl acrylate, ethyl methacrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate.

[0078] In one example, the second polymer includes at least one of polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer (e.g., methyl methacrylate-acrylonitrile copolymer), acrylate-acrylonitrile-ethylene copolymer, styrene-acrylic ester monomer-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, and ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate.

[0079] In the present invention, the first polymer and the second polymer may be the same or different.

[0080] In one example, the third coating layer is the same as or different from the second coating layer. Specifically, one or more of the following characteristics may be the same as or different from the thickness of the third coating layer and the thickness of the second coating layer, the particle size of the second particles and the particle size of the fourth particles, and the composition of the third coating layer and the composition of the second coating layer.

[0081] In one example, the coverage of the second coating layer on the surface of the first coating layer and the coverage of the third coating layer on the surface of the substrate layer may be the same as or different from each other.

[0082] In one example, the thickness of the substrate layer is 2 μm-10 μm (eg, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm).

[0083] In one example, the porosity of the substrate layer is 25%-70% (eg, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%).

[0084] In one example, the substrate layer comprises one or more of polyolefin (e.g., PE, PP), polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyethylene terephthalate, polybutylene terephthalate, poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), or derivatives of the foregoing polymers.

[0085] In one embodiment, the weight ratio of the fluoroethylene carbonate in the electrolyte is 15%-35%.

[0086] In one embodiment, the electrolyte includes a cyclic carbonate, which refers to a cyclic carbonate other than fluoroethylene carbonate.

[0087] In one example, the cyclic carbonate includes ethylene carbonate and / or propylene carbonate.

[0088] In one example, the weight percentage of the cyclic carbonate in the electrolyte is 5%-50% (eg, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%).

[0089] In one embodiment, the weight ratio of the cyclic carbonate in the electrolyte is 10%-25%.

[0090] In one embodiment, the weight ratio of the cyclic carbonate to the fluoroethylene carbonate is (0.2-1.5):1 (e.g., 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, or 1.5:1). Controlling the weight ratio of the cyclic carbonate to the fluoroethylene carbonate within the above range can further reduce the impedance of the CEI membrane and improve the flexibility of the CEI membrane while ensuring the mechanical stability of the membrane. When the weight ratio of the cyclic carbonate to the fluoroethylene carbonate is less than 0.2:1, the FEC content in the electrolyte is excessive or the cyclic carbonate content is too low, and the FEC tends to excessively corrode the coating, causing the coating's mechanical stability to be too poor, resulting in reduced mechanical strength of the diaphragm structure, which is not conducive to high-temperature bonding and the high-temperature voltage drop of the battery. When the weight ratio of the cyclic carbonate to the fluoroethylene carbonate is greater than 1.5:1, the FEC content in the electrolyte is too low or the carbonate content is too high, the FEC's corrosive effect on the coating is weakened, which is not conducive to reducing the impedance of the CEI membrane and improving the flexibility of the CEI membrane, and the fast charge voltage drop increases. In addition, the cyclic carbonate excessively swells the second particles, reducing the lithium ion permeability of the diaphragm, which is not conducive to improving the charge and discharge performance of the battery and reducing the battery rate performance.

[0091] In one example, the weight ratio of the cyclic carbonate to the fluoroethylene carbonate is (0.6-1.1):1.

[0092] According to a specific embodiment, the weight proportion of the fluoroethylene carbonate in the electrolyte is 13%-50%, the weight proportion of the cyclic carbonate in the electrolyte is 5%-50%, and the weight ratio of the cyclic carbonate to the weight of the fluoroethylene carbonate is (0.2-1.5):1.

[0093] According to a specific embodiment, the weight proportion of the fluoroethylene carbonate in the electrolyte is 15%-35%, the weight proportion of the cyclic carbonate in the electrolyte is 10%-25%, and the weight ratio of the cyclic carbonate to the weight of the fluoroethylene carbonate is (0.6-1.1):1.

[0094] In one example, the electrolyte includes lithium hexafluorophosphate, an organic solvent, and an additive.

[0095] In one example, the organic solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl formate (MF), methyl acetate (MA), methyl butyrate (MB), ethyl propionate (EP), propyl propionate (PP), ethyl butyrate, propyl acetate, and ethyl difluoroacetate.

[0096] In one embodiment, the additives include negative electrode surface film-forming additives, positive electrode surface film-forming additives, and positive and negative electrode current collector surface film-forming additives. They may also include additives that improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance. The additives may be one or more of dinitrile compounds, trinitrile compounds, and other nitrile compounds, lithium salt additives, fluorinated chain carbonates, fluorinated carboxylates, and sulfur-containing compounds.

[0097] Nitrile compounds include, but are not limited to, succinonitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 1,8-dicyanooctane, 1,9-dicyanononane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2,4-dimethylvaleronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,5-dicyanopentane, 2,6-dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 3,5-dioxa-heptanenitrile, 1,4-bis(cyanoethoxy)butane, ethylene glycol bis(2-cyanoethyl) ether, diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, One or more of tetraethylene glycol bis(2-cyanoethyl) ether, 3,6,9,12,15,18-hexaoxaeicosanoic acid dinitrile, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane, 1,5-bis(2-cyanoethoxy)pentane, ethylene glycol bis(4-cyanobutyl) ether, 1,4-dicyano-2-butene, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-2-methyl-3-hexene or 1,6-dicyano-2-methyl-5-methyl-3-hexene.

[0098] Trinitrile compounds include, but are not limited to, one or more of 1,3,5-pentanetricarboxylonitrile, 1,2,3-propanetricarboxylonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,6-tris(cyanoethoxy)hexane, or 1,2,5-tris(cyanoethoxy)pentane.

[0099] The lithium salt additives include, but are not limited to, one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt, lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, and lithium difluorobis(oxalatophosphate).

[0100] The sulfur-containing compound includes, but is not limited to, one or more of 1,3-propane sultone, vinyl sulfate, cyclic sulfate, chain sulfate, chain sulfonate, cyclic sulfonate, cyclic sulfonate, cyclic sulfite, chain sulfone, and cyclic sulfone.

[0101] The fluorinated chain carbonates include, but are not limited to, one or more of fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate.

[0102] In one example, based on the total weight of the electrolyte, the weight percentage of the lithium hexafluorophosphate is 5%-30% (e.g., 5%, 10%, 15%, 20%, 25%, or 30%), the weight percentage of the organic solvent is 0%-75% (e.g., 0, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%), and the weight percentage of the additive is 0%-20% (e.g., 0, 0.1%, 0.5%, 1%, 5%, 10%, 15%, or 20%). When the weight percentage of the organic solvent in the electrolyte is 0, it means that no organic solvent is present in the electrolyte. When the weight percentage of the additive in the electrolyte is 0%, it means that no additive is present in the electrolyte.

[0103] In one example, the positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium nickelate, lithium titanate, lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide.

[0104] In one example, the positive electrode active layer includes a positive electrode conductor and a positive electrode binder.

[0105] In one example, the positive electrode conductive agent includes one or more of conductive carbon black, carbon nanotubes, conductive graphite, and graphene.

[0106] In one example, the positive electrode binder includes one or more of polyvinylidene fluoride (PVDF), acrylic acid-modified PVDF, acrylic polymer, acrylic polymer, polytetrafluoroethylene, polyacrylonitrile, polyimide, acrylate-acrylonitrile copolymer, styrene-butadiene rubber, and styrene-propylene rubber.

[0107] In one example, based on the total weight of the positive electrode active layer, the weight proportion of the positive electrode active material is 90%-99% (for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%), the weight proportion of the positive electrode conductor is 0.5%-5% (for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%), and the weight proportion of the positive electrode binder is 0.5%-5%.

[0108] In one example, a charge cut-off voltage of the battery is greater than or equal to 4.5V.

[0109] In one example, the battery is a lithium-ion secondary battery.

[0110] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. All other examples obtained by persons of ordinary skill in the art based on the examples of the present invention without creative work are within the scope of protection of the present invention.

[0111] The following examples illustrate the batteries of the present invention.

[0112] Example 1 (1) Diaphragm The first particles (melamine cyanurate (MCA), with a characteristic group of triazine ring), adhesive (polyacrylic acid) and deionized water were mixed and stirred thoroughly to obtain a first slurry with a solid content of 25%. Based on the 100% solid mass of the slurry, the weight ratio of MCA to polyacrylic acid was 98%:2%. The first slurry was coated on one surface of the substrate layer (PE) by a gravure roller and dried in a multi-section oven at 60°C to form a first coating with a thickness of 1.5 μm. The second particles (methyl methacrylate-acrylonitrile copolymer) and the third particles (PVDF-HFP copolymer) were dispersed in deionized water (the weight ratio of the second particles to the third particles was 50%:50%). After stirring thoroughly, a second slurry with a solid content of 10% was obtained. The second slurry was coated on the surface of the first coating by a gravure roller and dried in a multi-section oven at 60°C to form a second coating (thickness of 0.7 μm). The fourth particles (methyl methacrylate-acrylonitrile copolymer) were dispersed in deionized water and stirred thoroughly to obtain a third slurry with a solid content of 10%. The third slurry was coated on the surface of the other side of the substrate layer by a gravure roller and dried in a multi-section oven at 60°C to form a third coating.

[0113] Among them, within any 100μm×100μm area of ​​the first surface, the number of primary particles with a particle size less than or equal to 0.3μm accounts for 2.1% of the number of primary particles; the weight proportion A of the characteristic group in the first surface is 28.3%, the weight proportion B of the ester group in the first surface is 4.1%, the Dv10 of the first particle is 0.3μm, the Dv98 of the first particle is 3.8μm, the Dv95 of the second particle is 0.8μm, the average particle size d1 of the secondary particles in the third particle is 6.4μm, d1 / d2=6.4 / 0.8=8, the coverage of the second coating on the surface of the first coating is 23%, and the coverage of the third coating on the surface of the substrate layer is 15%.

[0114] (2) Electrolyte In an argon-filled glove box (moisture <1ppm, oxygen <1ppm), ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate solvents were mixed into a uniform solvent, and LiPF6, 1,3,6-hexanetrinitrile, and fluoroethylene carbonate were slowly added. After stirring, an electrolyte was obtained. Among them, the weight proportion of LiPF6 in the electrolyte was 20%, the weight proportion of 1,3,6-hexanetrinitrile was 3%, the weight proportion of fluoroethylene carbonate was 25%, the weight proportion of cyclic ethylene carbonate was 18% (the weight ratio of ethylene carbonate to propylene carbonate was 0.5:1), the weight ratio of propyl propionate to ethyl propionate was 5:2, and the weight ratio of cyclic carbonate to fluoroethylene carbonate was 0.72.

[0115] (3) Positive electrode The positive electrode active material (lithium cobalt oxide), positive electrode binder (polyvinylidene fluoride (PVDF500)), and positive electrode conductive agent (Super P: carbon nanotubes (weight ratio) = 2:1) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 98:2:2. The mixture was continuously stirred in a blender to form a uniform, fluid positive electrode slurry. Subsequently, the positive electrode slurry was coated on both sides of a 10μm-thick aluminum foil to form a positive electrode active layer. The mixture was then dried in a 120°C vacuum oven for 6 hours. The positive electrode sheets were then rolled and slit.

[0116] (4) Negative electrode Graphite, silicon carbon (Dv50 = 7μm), conductive material (carbon black: carbon nanotubes = 1:1), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber were mixed in an aqueous solvent at a weight ratio of 92:6:1:0.5:0.5. This mixture was continuously stirred in a blender to form a uniform, fluid negative electrode slurry. The slurry was then coated on both sides of a 10μm-thick current collector copper foil and dried in a 120°C vacuum oven for 6 hours. The negative electrode sheets were then rolled and slit.

[0117] (5) Lithium-ion batteries The positive electrode sheet prepared in step (3), the separator prepared in step (1), and the negative electrode sheet prepared in step (4) are wound to prepare a bare cell; the bare cell is then placed in an aluminum-plastic film, and the electrolyte prepared in step (2) is injected into the dried bare cell. After vacuum packaging, room temperature standing, high-temperature formation, and other processes, a lithium-ion battery is obtained.

[0118] Example 2 group This set of embodiments is used to illustrate the impact when the proportion of the number of primary particles with a particle size less than or equal to 0.3 μm in the total number of primary particles changes within any 100 μm×100 μm area of ​​the first surface.

[0119] Example 2a The method is carried out in accordance with Example 1, except that, within any 100 μm×100 μm area of ​​the first surface, the number of the primary particles having a particle size less than or equal to 0.3 μm accounts for 0.03% of the total number of the primary particles.

[0120] Example 2b The method is carried out in accordance with Example 1, except that, within any 100 μm×100 μm area of ​​the first surface, the number of the primary particles having a particle size less than or equal to 0.3 μm accounts for 3.91% of the total number of the primary particles.

[0121] Example 3 group This set of examples is used to illustrate the impact produced when the coverage of the second coating on the surface of the first coating changes.

[0122] Example 3a The process was carried out with reference to Example 1, except that the coverage of the second coating on the surface of the first coating was 15.2%.

[0123] Example 3b The process was carried out with reference to Example 1, except that the coverage of the second coating on the surface of the first coating was 35.7%.

[0124] Example 3c The process was carried out with reference to Example 1, except that the coverage of the second coating on the surface of the first coating was 50%.

[0125] Example 3d The process was carried out with reference to Example 1, except that the coverage of the second coating on the surface of the first coating was 10.9%.

[0126] Example 3e The process was carried out with reference to Example 1, except that the coverage of the second coating on the surface of the first coating was 52.1%.

[0127] Example 4 Group This set of examples is used to illustrate the effects produced when the Dv10 and / or Dv98 of the first particles are changed.

[0128] Example 4a The same process was carried out as in Example 1, except that the Dv10 of the first particles was 0.02 μm and the Dv98 of the first particles was 2.2 μm.

[0129] Example 4b The same process was carried out as in Example 1, except that the Dv10 of the first particles was 0.48 μm and the Dv98 of the first particles was 4.9 μm.

[0130] Example 4c The same process was carried out as in Example 1, except that the Dv10 of the first particles was 0.55 μm and the Dv98 of the first particles was 5.2 μm.

[0131] Example 5 Group This set of embodiments is used to illustrate the impact produced when d1 / d2 changes.

[0132] Example 5a The process is carried out in accordance with Example 1, except that the average particle size d1 of the secondary particles in the third particles is 10 μm, the Dv95 of the second particles is 0.53, and d1 / d2=10 / 0.53=18.9.

[0133] Example 5b The process is carried out in accordance with Example 1, except that the average particle size d1 of the secondary particles in the third particles is 5.5 μm, the Dv95 of the second particles is 4.91, and d1 / d2=5.5 / 4.91=1.1.

[0134] Example 5c The process is carried out in accordance with Example 1, except that the average particle size d1 of the secondary particles in the third particles is 13.2 μm, the Dv95 of the second particles is 0.53, and d1 / d2=13.2 / 0.53=24.9.

[0135] Example 5d The process is carried out in accordance with Example 1, except that the average particle size d1 of the secondary particles in the third particles is 3.1 μm, the Dv95 of the second particles is 1.9, and d1 / d2=3.1 / 1.9=1.6.

[0136] Example 5e The process is carried out in accordance with Example 1, except that the average particle size d1 of the secondary particles in the third particles is 14.5 μm, the Dv95 of the second particles is 0.53, and d1 / d2=14.5 / 0.53=27.4.

[0137] Example 5f The process is carried out in accordance with Example 1, except that the average particle size d1 of the secondary particles in the third particles is 2.2 μm, the Dv95 of the second particles is 2.4, and d1 / d2=2.2 / 2.4=0.9.

[0138] Example 6 This set of examples is used to illustrate the effects of changing the weight ratio of fluoroethylene carbonate in the electrolyte.

[0139] Example 6a The process was carried out in accordance with Example 1, except that the weight proportion of fluoroethylene carbonate in the electrolyte was 13%, and the ratio of the weight of the cyclic carbonate to the weight of the fluoroethylene carbonate was 1.38.

[0140] Example 6b The process was carried out in accordance with Example 1, except that the weight proportion of fluoroethylene carbonate in the electrolyte was 15%, and the ratio of the weight of cyclic carbonate to the weight of fluoroethylene carbonate was 1.2.

[0141] Example 6c The process was carried out in accordance with Example 1, except that the weight proportion of fluoroethylene carbonate in the electrolyte was 35%, and the ratio of the weight of cyclic carbonate to the weight of fluoroethylene carbonate was 0.51.

[0142] Example 6d The process was carried out in accordance with Example 1, except that the weight proportion of fluoroethylene carbonate in the electrolyte was 50%, and the ratio of the weight of cyclic carbonate to the weight of fluoroethylene carbonate was 0.36.

[0143] Example 7 Group This set of examples is used to illustrate the effects of varying the weight ratio of cyclic carbonate to fluoroethylene carbonate.

[0144] Example 7a The process was carried out in accordance with Example 1, except that the weight proportion of the cyclic carbonate in the electrolyte was 5%, and the weight ratio of the cyclic carbonate to the fluoroethylene carbonate was 0.2.

[0145] Example 7b The process was carried out in accordance with Example 1, except that the weight proportion of the cyclic carbonate in the electrolyte was 10%, and the weight ratio of the cyclic carbonate to the fluoroethylene carbonate was 0.4.

[0146] Example 7c The process was carried out in accordance with Example 1, except that the weight proportion of the cyclic carbonate in the electrolyte was 25%, and the ratio of the weight of the cyclic carbonate to the weight of the fluoroethylene carbonate was 1.

[0147] Example 7d The process was carried out with reference to Example 1, except that the weight proportion of the cyclic carbonate in the electrolyte was 37%, and the ratio of the weight of the cyclic carbonate to the weight of fluoroethylene carbonate was 1.48.

[0148] Example 7e The method is carried out with reference to Example 1, except that the weight proportion of fluoroethylene carbonate in the electrolyte is 31%, the weight proportion of cyclic carbonate in the electrolyte is 50%, the ratio of the weight of cyclic carbonate to the weight of fluoroethylene carbonate is 1.61, the weight proportion of LiPF6 in the electrolyte is 18%, the weight proportion of 1,3,6-hexanetrinitrile is 1%, and propyl propionate and ethyl propionate are not present in the electrolyte.

[0149] Example 7f The process was carried out with reference to Example 1, except that the weight proportion of fluoroethylene carbonate in the electrolyte was 50%, the weight proportion of cyclic carbonate in the electrolyte was 5%, and the ratio of the weight of cyclic carbonate to the weight of fluoroethylene carbonate was 0.1.

[0150] Example 8 Group This set of examples is used to illustrate the effects produced when the composition of the first particles is changed.

[0151] Example 8a The process is carried out in accordance with Example 1, except that the component of the first particle is uracil.

[0152] Example 8b The same process is carried out as in Example 1, except that the first particles are made of diethylaluminum hypophosphite.

[0153] Example 8c The process is carried out in accordance with Example 1, except that the first particles are composed of melamine thiocyanate.

[0154] Example 8d The process is carried out in accordance with Example 1, except that the component of the first particle is cytosine.

[0155] Example 9 Group This set of examples is used to illustrate the effects produced when the composition of the second particles is changed.

[0156] Example 9a The same process as in Example 1 was carried out, except that the second particles were made of acrylate-ethylene copolymer.

[0157] Example 9b The process is carried out in accordance with Example 1, except that the second particles are made of PMMA.

[0158] Example 10 Group This set of examples is used to illustrate the effects produced when the composition of the third particles is changed.

[0159] Example 10a The process is carried out in accordance with Example 1, except that the third particle is made of PVDF.

[0160] Example 10b The same process is carried out as in Example 1, except that the third particles are made of polyvinyl fluoride.

[0161] Example 11 Group This set of examples is intended to illustrate the effects of varying the specific selection of cyclic ethylene carbonate.

[0162] Example 11a The same process is carried out as in Example 1, except that the cyclic ethylene carbonate is all EC.

[0163] Example 11b The same process is carried out as in Example 1, except that the cyclic ethylene carbonate is all PC.

[0164] Example 12 The process is carried out in accordance with Example 1, except that the first slurry is coated on both sides of the substrate layer to form a first coating layer, the second slurry is coated on both sides of the first coating layer to form a second coating layer, and the diaphragm does not include a third coating layer.

[0165] Example 13 The method was carried out in accordance with Example 1, except that the first particles (melamine cyanurate (MCA), the characteristic group being a triazine ring), the adhesive (polyacrylic acid), the second particles (methyl methacrylate-acrylonitrile copolymer), the third particles (PVDF-HFP copolymer) and deionized water were mixed and stirred thoroughly to obtain a coating slurry having a solid content of 15%, wherein the ratio of the first particles: the second particles: the third particles: the adhesive (weight ratio) was 85:8:6:1. The coating slurry was applied to the surface of one side of the substrate layer by a gravure roller, and dried in a multi-section oven at 60°C to form a coating layer. The third slurry was applied to the surface of the other side of the substrate layer by a gravure roller, and dried in a multi-section oven at 60°C to form a third coating layer.

[0166] Example 14 The same procedure as in Example 1 was followed, except that the third particle was absent.

[0167] Comparative Example 1 The process is carried out in accordance with Example 1, except that the first particles are made of aluminum oxide.

[0168] Comparative Example 2 The process is carried out in accordance with Example 1, except that the first particles are made of polyimide.

[0169] Comparative Example 3 The method is carried out in accordance with Example 1, except that, within any 100 μm×100 μm area of ​​the first surface, the number of the primary particles having a particle size less than or equal to 0.3 μm accounts for 0 of the total number of the primary particles.

[0170] Comparative Example 4 The method is carried out in accordance with Example 1, except that, within any 100 μm×100 μm area of ​​the first surface, the number of the primary particles having a particle size less than or equal to 0.3 μm accounts for 4.3% of the total number of the primary particles.

[0171] Comparative Example 5 The process was carried out in accordance with Example 1, except that the weight proportion of fluoroethylene carbonate in the electrolyte was 12%, and the ratio of the weight of the cyclic carbonate to the weight of the fluoroethylene carbonate was 1.5.

[0172] Comparative Example 6 The process was carried out in accordance with Example 1, except that the weight proportion of fluoroethylene carbonate in the electrolyte was 51.12%, and the ratio of the weight of cyclic carbonate to the weight of fluoroethylene carbonate was 0.35.

[0173] Test Case The lithium ion batteries prepared in the examples and comparative examples were tested as follows: 1. Battery polarization Resistance R1 was measured by applying a discharge pulse of 2.5C for 10 seconds at 100% state of charge (SOC) at 25°C, and resistance R2 was measured by applying a discharge pulse of 2.5C for 10 seconds at 50% state of charge (SOC) at 25°C. Battery polarization ΔR=R1-R2.

[0174] 2. Fast charging voltage drop test At 25°C, charge the lithium-ion battery at a constant current of 3C to a voltage of 4.5V. Then, charge it at a constant voltage of 4.5V to a current of 0.05C. Discharge it at a constant current of 1C to a voltage of 3.0V. Let it rest for 5 minutes, then measure the voltage and record it as the pre-storage voltage. Then, store it at -20°C for 24 hours and re-measure the voltage and record it as the post-storage voltage. Voltage drop = pre-storage voltage - post-storage voltage.

[0175] 3. Room temperature long cycle impedance change rate test The lithium-ion battery was transferred to a 25°C environment, allowed to stand for 30 minutes, discharged at a constant current of 0.2C to 3.0V, allowed to stand for 5 minutes, then charged at 0.5C to 4.5V, then charged at a constant voltage to a cutoff current of 0.05C, allowed to stand for 5 minutes, and the initial fully charged state impedance value R1 was measured using an electrochemical workstation. It was then discharged at a constant current of 0.7C to 3.0V, and then cycled 1000T according to the following steps: charging at 0.5C to 4.5V, then charging at a constant voltage to a cutoff current of 0.05C, allowed to stand for 5 minutes, and discharging at a constant current of 0.7C to 3.0V. After the cycle is completed, it is charged at 0.5C to 4.5V, then charged at a constant voltage to a cutoff current of 0.05C, allowed to stand for 5 minutes, and the full-charge state impedance value R2 after the cycle is measured using an electrochemical workstation. The rate of change is calculated as: [(R2-R1) / R1]×100%.

[0176] 4. Room temperature long cycle capacity retention test Under 25℃±2℃ environment, charge at 0.7C constant current and constant voltage to the upper limit voltage of 4.5V, cut off at 0.05C, record the initial thickness P0, then discharge at 0.2C constant current to the lower limit voltage of 3.0V, record the initial discharge capacity as C0, rest for 10min, cycle mode: charge at 3C constant current and constant voltage to 4.25V, cut off at 2C, switch to 2C constant current and constant voltage to charge to 4.48V, cut off at 1.5C, switch to 1.5C constant current and constant voltage to charge to the upper limit voltage of 4.5V, cut off at 0.18C, rest for 5min, discharge at 0.7C to the lower limit voltage of 3.0V. After 1000T cycle, charge at 0.7C constant current and constant voltage to the upper limit voltage, cut off at 0.05C, record the final thickness P1, then discharge at 0.2C constant current to the lower limit voltage, record the initial discharge capacity as C1.

[0177] Capacity retention rate: C=C1 / C0*100% 5. Normal temperature cycle impedance The lithium-ion battery was transferred to a 25°C environment, allowed to stand for 30 minutes, discharged at a constant current of 0.2C to 3.0V, allowed to stand for 5 minutes, then charged at 0.5C to 4.5V, then charged at a constant voltage to a cutoff current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.7C to 3.0V. The battery was then cycled for 10T according to the following steps: charged at 0.5C to 4.5V, then charged at a constant voltage to a cutoff current of 0.05C, allowed to stand for 5 minutes, and discharged at a constant current of 0.7C to 3.0V. After the cycle was completed, the battery was charged at 0.5C to 4.5V, then charged at a constant voltage to a cutoff current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.7C to 3.0V. After the cycle was completed, the battery was charged at 0.5C to 4.5V, then charged at a constant voltage to a cutoff current of 0.05C, allowed to stand for 5 minutes, and the impedance value R1 of the fully charged state after the cycle was tested using an electrochemical workstation.

[0178] 6. 45℃ rate performance The lithium-ion battery was left at 45±2°C for 60 minutes, discharged at 0.2C to 3.0V, left at 10 minutes, and then charged at 1.2C to 4.5V. Then, it was charged at a constant voltage with a cutoff current of 0.05C, left at 10 minutes, and discharged at 1C to 3.0V. After 10 minutes of rest, the discharge capacity was recorded as Q0. Then, it was charged at a constant current of 2.5C to 4.5V, then charged at a constant voltage with a cutoff current of 0.05C, left at 10 minutes, and discharged at 1C to 3.0V. After 10 minutes of rest, the discharge capacity was recorded as Q2. Capacity retention = (Q2 / Q0) × 100%.

[0179] 7. Change rate of internal resistance during high temperature storage At 60°C, charge the lithium-ion battery at a constant current of 3C to a voltage of 4.5V, then charge it at a constant voltage of 4.5V to a current of 0.05C, and then discharge it at a constant current of 1C to a voltage of 3.0V. Let it rest for 5 minutes, and then measure its resistance, which is recorded as the resistance before storage, R1. Then, store it at 60°C for 7 days and remeasure its resistance, which is recorded as the resistance after storage, R2. The storage internal resistance change rate is: [(R2-R1) / R1]×100%.

[0180] The obtained results are recorded in Table 1.

[0181] Table 1 It can be seen from Table 1 that, by comparing the comparative example and the embodiment, the impedance difference between 100% SOC and 50% SOC of the battery of the embodiment is significantly reduced, the normal temperature cycle impedance is reduced, the normal temperature cycle impedance change rate is reduced, the normal temperature cycle capacity retention rate is improved, the rate performance is significantly improved, the fast charging voltage drop is significantly reduced, and the high temperature storage internal resistance change rate is significantly reduced, indicating that by simultaneously controlling the proportion of the number of primary particles with a particle size less than or equal to 0.3 μm in the primary particles of the second particles per unit area of ​​the coating surface and the weight proportion of fluoroethylene carbonate in the electrolyte, the cycle impedance of the battery is reduced and the long cycle performance and rate performance of the battery are improved.

[0182] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A battery, wherein: The battery includes a positive electrode sheet, a separator and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer located on one side or both sides of the positive electrode current collector. The separator includes a substrate layer and a coating located on one side or both sides of the substrate layer. The coating corresponds to the positive electrode active layer. The coating includes first particles and second particles. The first particles include a first compound. The first compound includes a characteristic group. The characteristic group includes one or more of a triazine ring, a pyrimidine ring and a phosphorus-oxygen double bond. The second particles include a first polymer. The first polymer is an ester-containing polymer. The second particles include primary particles. The surface of the coating away from the substrate layer is the first surface. Within any 100 μm×100 μm area of ​​the first surface, the number of primary particles with a particle size of less than or equal to 0.3 μm accounts for 0.01%-4% of the total number of primary particles. The electrolyte includes fluoroethylene carbonate, and the weight proportion of the fluoroethylene carbonate in the electrolyte is 13%-50%.

2. The battery according to claim 1, wherein The electrolyte includes a cyclic carbonate, and the weight ratio of the cyclic carbonate to the fluoroethylene carbonate is (0.2-1.5):1; And / or, the weight proportion of the fluoroethylene carbonate in the electrolyte is 15%-35%.

3. The battery according to claim 2, wherein The cyclic carbonate includes ethylene carbonate and / or propylene carbonate; And / or, the weight proportion of the cyclic carbonate in the electrolyte is 5%-50%; And / or, the weight ratio of the cyclic carbonate to the fluoroethylene carbonate is (0.6-1.1):

1.

4. The battery according to claim 1, wherein The weight proportion of the ester groups in the first surface is 1%-20%.

5. The battery according to claim 1, wherein The coating includes third particles, the components of the third particles include fluorine-containing polymers, and the diaphragm satisfies the following relationship: 1≤d1 / d2≤25, wherein d1 is the average particle size of the secondary particles in the third particles, in μm, and d2 is the Dv95 of the second particles, in μm.

6. The battery according to claim 5, wherein The average particle size d1 of the secondary particles in the third particles is 2 μm-15 μm; and / or, the Dv95 of the second particles is 0.5 μm-5 μm; and / or, the monomers forming the fluorine-containing polymer include one or more of vinylidene fluoride, tetrafluoroethylene, hexafluoroethylene, and hexafluoropropylene; And / or, the fluorine-containing polymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, ethylene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer and tetrafluoroethylene-hexafluoropropylene copolymer.

7. The battery according to claim 1, wherein The Dv10 of the first particles is 0.01 μm-0.5 μm; and / or, the Dv98 of the first particles is 2 μm-5 μm; and / or, the first compound comprises one or more of 2-phenylpyrimidine-4-carboxaldehyde, 1,4,6-dihydroxy-2-phenylpyrimidine, 5,6-diamino-2-phenyl-pyrimidine-4-ol, 4,6-dimethyl-2-phenylpyrimidine, uracil, cytosine, 2,4-dimercaptopyrimidine, 2,4-dimercapto-5,6-diaminopyrimidine, ammonium polyphosphate, diethylaluminum hypophosphite, melamine cyanurate, melamine thiocyanate, thiocyanic acid and 2,4,6-tris(4-hydroxyphenyl)-1,3,5-triazine; and / or, the first polymer comprises an acrylic polymer; and / or, the monomers forming the first polymer include one or more of methyl methacrylate, butyl acrylate, n-propyl acrylate, octyl acrylate, ethyl methacrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, cyclohexyl acrylate and 2-hydroxyethyl acrylate; And / or, the first polymer includes at least one of polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer, acrylate-ethylene copolymer, acrylate-acrylonitrile-ethylene copolymer, styrene-acrylate monomer-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer and ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate.

8. The battery according to any one of claims 1 to 7, wherein The coating comprises a first coating layer and a second coating layer, the first coating layer being located between the substrate layer and the second coating layer, the first coating layer comprising first particles, and the second coating layer comprising second particles and optionally third particles; And / or, when the coating is located on one side of the substrate layer, the diaphragm further comprises a third coating, the third coating is located on the other side of the substrate layer, the third coating comprises fourth particles, the fourth particles are arranged in a stacked manner in the third coating, the components of the fourth particles include a second polymer, and the second polymer includes a polymer containing an ester group.

9. The battery according to claim 8, wherein The thickness of the first coating is 0.2 μm-4 μm; And / or, the first coating layer includes an adhesive, and based on the total weight of the first coating layer, the weight of the first particles accounts for 90%-99%, and the weight of the adhesive accounts for 1%-10%; and / or, the thickness of the second coating layer is 0.5 μm-5 μm; And / or, based on the total weight of the second coating layer, the weight of the second particles accounts for 10%-100%, and the weight of the third particles accounts for 0%-90%; and / or, the coverage of the second coating on the surface of the first coating is 15%-50%; and / or, the second polymer comprises an acrylic polymer; and / or, the monomers forming the second polymer include one or more of methyl methacrylate, butyl acrylate, n-propyl acrylate, octyl acrylate, ethyl methacrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, cyclohexyl acrylate and 2-hydroxyethyl acrylate; And / or, the second polymer includes at least one of polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer, acrylate-acrylonitrile-ethylene copolymer, styrene-acrylate monomer-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer and ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate.

10. The battery according to claim 1, wherein The positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium nickelate, lithium titanate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide, lithium iron phosphate and lithium manganate; And / or, the electrolyte further comprises lithium hexafluorophosphate, and the weight proportion of lithium hexafluorophosphate in the electrolyte is 5%-30%; And / or, the charging cut-off voltage of the battery is greater than or equal to 4.5V.

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