A battery

Abstract

The application relates to the technical field of batteries, in particular to a battery. The battery comprises a positive electrode sheet, a diaphragm and an electrolyte, the coating of the diaphragm corresponds to the positive active layer of the positive electrode sheet, the coating comprises first particles and second particles, the composition of the first particles comprises one or more characteristic groups of triazine rings, pyrimidine rings and phosphorus-oxygen double bonds, the composition of the second particles comprises an ester group-containing polymer, the second particles comprise primary particles, in an area of 100 mu m*100 mu m of a first surface of the coating away from the substrate layer, the number ratio of the primary particles with a particle size less than or equal to 0.3 mu m in the primary particles is 0.01%-4%; the electrolyte comprises fluoroethylene carbonate, and the weight ratio of the fluoroethylene carbonate in the electrolyte is 13%-50%. The battery can reduce the impedance of the CEI film, improve the softness of the CEI film, and improve the cycle stability and rate performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery. BACKGROUND

[0002] With the wide application of portable electronic devices and electric vehicles, as an efficient energy storage solution, the performance optimization of lithium ion batteries has always been a hot research topic. However, with the increase of the number of battery charge and discharge cycles, the performance of the positive active material will gradually decrease, mainly manifested as capacity attenuation and internal resistance increase. This not only affects the service life of the battery, but also limits its further development in high energy density and high power application scenarios. SUMMARY

[0003] During the charging and discharging process of the lithium ion battery, a solid electrolyte interface film (CEI film) will be formed on the surface of the positive active material. This film can protect the positive active material from the corrosion of the electrolyte to some extent, and its performance has a crucial influence on the overall performance of the battery. The traditional CEI film usually has some shortcomings, such as high impedance and poor mechanical properties, which will cause large polarization phenomenon of the battery during the cycle process, and further accelerate the performance degradation of the battery. Specifically, the high impedance CEI film will increase the internal resistance of the battery, reduce the charge and discharge efficiency of the battery, and also cause the performance decline of the battery during high-rate charge and discharge; while the CEI film with poor mechanical properties and lack of flexibility is difficult to adapt to the volume change of the positive active material during the charge and discharge process, and is easy to cause the rupture and continuous regeneration of the film, on the one hand, it will thicken the CEI film and increase the impedance of the CEI film, on the other hand, it will also increase the side reaction of the interface, further aggravating the capacity attenuation of the battery.

[0004] Therefore, in order to improve the cycle performance of the positive active material, prolong 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 active material.

[0005] In view of this, in order to solve the problems of high impedance and poor mechanical properties of the CEI film in the prior art, the present application provides a battery. The battery of the present application can reduce the impedance of the CEI film and improve the softness of the CEI film, effectively reduce the internal resistance of the battery, reduce the polarization phenomenon, and at the same time, enhance the protection effect of the CEI film on the positive active material, so that the CEI film can better adapt to the volume change of the positive material during the charge and discharge process, thereby significantly improving the cycle stability and charge and discharge performance under high rate of the battery.

[0006] To achieve the above object, the present application provides a battery, which comprises 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 side or both sides of the positive electrode current collector, the separator comprises a substrate layer and a coating layer located on one side or both sides of the substrate layer, the coating layer corresponds to the positive electrode active layer, the coating layer comprises first particles and second particles, the composition of the first particles comprises a first compound, the first compound comprises a characteristic group, the characteristic group comprises one or more of a triazine ring, a pyrimidine ring and a phosphorus-oxygen double bond, the composition of the second particles comprises a first polymer, the first polymer is a polymer containing an ester group, the second particles comprise primary particles, the surface of the coating layer away from the substrate layer is a first surface, in any 100 mu m*100 mu m area of the first surface, the number ratio of the primary particles with a particle size less than or equal to 0.3 mu m in the primary particles is 0.01%-4%;

[0007] The electrolyte comprises fluoroethylene carbonate, and the weight ratio of the fluoroethylene carbonate in the electrolyte is 13%-50%.

[0008] Compared with the prior art, the present application has at least the following advantages:

[0009] The battery of the present application can form an anion-derived interface rich in LiF and ester groups on the surface of the positive electrode sheet through the synergistic cooperation of the first particles, 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 lower impedance and higher flexibility, the polarization phenomenon of the battery is reduced, the cycle impedance of the battery is reduced, and the cycle performance and rate performance of the battery are improved; at the same time, by controlling the number ratio of the primary particles with a particle size less than or equal to 0.3 mu m in the primary particles of the second particles in the 100 mu m*100 mu m area of the coating layer 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 electron-withdrawing group-containing substances and the second particles dissolve an appropriate amount of ester group-containing substances, and the excessive corrosion of the first particles and the second particles by the fluoroethylene carbonate in the electrolyte is avoided.

[0010] Other features and advantages of the present application will be described in detail in the following specific embodiments.

[0011] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges and values should be interpreted as approximations. The endpoints of the ranges and values are provided as a separate point for the convenience of the reader. The ranges and values are approximate values and are understood to be encompassed by the values within the range. The approximate values are understood to be inclusive of the values within the range. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 Fig. 1 shows a schematic cross-sectional view of a separator of the present application.

[0013] Figure 2 Fig. 2 shows another schematic cross-sectional view of a separator of the present application.

[0014] Figure 3 Fig. 3 shows a SEM image of a separator of the present application. DETAILED DESCRIPTION

[0015] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application. In this document, unless specifically stated otherwise, data ranges are inclusive of the endpoints.

[0016] It should be noted that the terms "first", "second", and the like in the present application are only used to distinguish different substances or uses, and do not represent the difference in order.

[0017] The present application provides a battery, the battery comprising a positive electrode sheet, a separator and an electrolyte, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active layer located on one or both sides of the positive electrode current collector, the separator comprising a substrate layer and a coating layer located on one or both sides of the substrate layer, the coating layer corresponding to the positive electrode active layer, the coating layer comprising first particles and second particles, the composition of 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 composition of 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 layer away from the substrate layer being a first surface, the number ratio of the primary particles with a particle size less than or equal to 0.3 μm in the first surface within any 100 μm x 100 μm area of the first surface being 0.01%-4% (for example, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or 4%) of the number of the primary particles;

[0018] The electrolyte comprises fluoroethylene carbonate, the weight ratio of the fluoroethylene carbonate in the electrolyte being 13%-50% (for example, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48% or 50%).

[0019] As Figure 1As 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 2 As 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.

[0020] 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.

[0021] 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-.

[0022] 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.

[0023] It is found through research that high content of fluoroethylene carbonate (FEC) in the electrolyte can slightly corrode the first particles and the second particles in the coating of the separator, so that certain electron-withdrawing groups (i.e., one or more of a triazine ring, a pyrimidine ring, and a phosphorus-oxygen double bond) and ester groups are generated on the surface of the coating of the separator, thereby being able to increase the content of FEC, PF6 - and ester groups at the interface between the separator and the positive electrode, promote the entry of anions (such as PF6 - ) into the Li + solvation layer, form a LiF and ester group-rich anion-derived interface, and reduce the overall interface film (including the CEI film) on the surface of the positive electrode active material to have lower impedance and higher flexibility, reduce the polarization phenomenon during the normal-temperature cycle of the battery, reduce the cycle impedance of the battery, improve the long-cycle performance of the battery, while reducing the fast-charging voltage drop, improving the charge-discharge performance of the battery at a large rate, and improving the rate capability of the battery.

[0024] Meanwhile, in order to ensure that the electron-withdrawing groups in the first particles and the ester groups in the second particles are appropriately dissolved out, and to avoid excessive corrosion of the first particles and the second particles by fluoroethylene carbonate in the electrolyte, the battery of the present application simultaneously controls the proportion of the number of primary particles with a particle size of less than or equal to 0.3 microns in the primary particles of the second particles per unit area on the surface of the coating, and the weight proportion of fluoroethylene carbonate in the electrolyte.

[0025] The primary particles with a smaller particle size are more easily corroded by fluoroethylene carbonate, and controlling the proportion of the number of primary particles with a particle size of less than or equal to 0.3 microns in the primary particles of the second particles per unit area on the surface of the coating can ensure that there are appropriate primary particles with a smaller particle size in the coating, which facilitates the appropriate dissolution of ester groups under the corrosion of fluoroethylene carbonate, thereby being able to increase the content of ester groups at the interface between the separator and the positive electrode, while 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 appropriately dissolved out, avoiding excessive corrosion of the first particles and the second particles by fluoroethylene carbonate, which affects the mechanical stability of the separator, on the other hand, the content of FEC, PF6 - and ester groups at the interface between the separator and the positive electrode is increased, and the entry of anions PF6 - into the Li +The solvation layer forms a LiF and ester group-rich anion-derived interface, and the fluoroethylene carbonate can form a LiF and ester group-rich CEI film together with the ester group, reduce the impedance of the CEI film and improve the flexibility of the CEI film, so that the interface film of the overall surface of the positive active material has lower impedance and higher flexibility, reduces the polarization phenomenon during the normal temperature cycle of the battery, reduces the cycle impedance of the battery, improves the long cycle performance of the battery, reduces the fast charging voltage drop, improves the charge and discharge performance of the battery at high rate, and improves the rate performance of the battery. Moreover, 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 in a unit area of the coating surface within the above range can also ensure that there are more primary particles with a larger particle size in the coating, which are not easily corroded by fluoroethylene carbonate, and can ensure the overall structural stability of the second particles and avoid excessive dissolution of the characteristic groups.

[0026] When the number of primary particles with a particle size less than or equal to 0.3 μm in the first surface 100 μm x 100 μm area is less than 0.01% of the number of primary particles, 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 is too low, and the fluoroethylene carbonate is difficult to corrode the second particles with a larger particle size, so that the ester group is difficult to dissolve or not to dissolve, the content of the ester group at the interface between the separator and the positive electrode is low, which is not conducive to the formation of a LiF and ester group-rich CEI film, the impedance of the CEI is still high and the flexibility is poor, the capacity decay of the battery is intensified, and the high-rate charge and discharge performance is poor. When the number of primary particles with a particle size less than or equal to 0.3 μm in the first surface 100 μm x 100 μm area is more than 4% of the number of primary particles, 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 is too high, and the degree of corrosion of the fluoroethylene carbonate to the second particles is large, which is not conducive to maintaining the overall structural stability of the second particles, the mechanical stability of the separator is poor, and the interface stability between the separator and the positive electrode is poor, which increases the interface impedance and reduces the cycle stability and rate performance of the battery.

[0027] When the weight percentage of the fluoroethylene carbonate in the electrolyte is less than 13%, the corrosion degree of the fluoroethylene carbonate on the first particles and the second particles is low, which is not conducive to the dissolution of the characteristic groups and the ester groups, and is not conducive to the generation of the anion-derived interface, and thus the impedance of the CEI film cannot be effectively reduced and the softness of the CEI film cannot be effectively improved, and the cycle stability of the battery is low, and the charge-discharge performance at high rate is reduced. When the weight percentage of the fluoroethylene carbonate in the electrolyte is more than 50%, the corrosion degree of the fluoroethylene carbonate on the first particles and the second particles is too large, which is not conducive to maintaining the overall mechanical stability of the separator, and the separator and the battery are prone to delamination, and the interface stability between the separator and the positive electrode is poor, which increases the interface impedance and reduces the cycle stability and the rate performance of the battery.

[0028] It can be understood that, in the present application, the corrosion of the fluoroethylene carbonate on the first particles and the second particles does not mean that the particle state of all the first particles and the second particles disappears or 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 all disappears or partially disappears, and it can also be that part of the 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 all be retained.

[0029] In the present application, the characteristic groups dissolved from the first particles and the ester groups dissolved from the second particles are not in the form of groups, but substances with the groups, which can be one or more of small molecules, monomers, oligomers, and ions.

[0030] In the present application, the percentage 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 in the unit area of the coating surface and the weight percentage of the fluoroethylene carbonate in the electrolyte are simultaneously controlled, which has reduced the cycle impedance of the battery and improved the long cycle performance and the rate performance of the battery compared with the prior art. In order to further improve the effect, one or more of the technical features can be further optimized.

[0031] In an example, the percentage of the number of the primary particles with a particle size less than or equal to 0.3 μm in the primary particles in the area of 100 μm x 100 μm of the first surface is 1%-3.5%.

[0032] In an example, the first compound comprises one or more of 2-phenylpyrimidine-4- carboxaldehyde, 1,4,6-dihydroxy-2-phenylpyrimidine, 5,6-diamino-2-phenyl-pyrimidin-4-ol, 4,6-dimethyl-2-phenylpyrimidine, uracil, cytosine, 2,4-dimercaptopyrimidine, 2,4-dimercapto-5,6-diaminopyrimidine, ammonium polyphosphate, aluminum diethylphosphinate, melamine cyanurate, melamine trimer thiocyanate, thiocyanic acid, and 2,4,6-tris(4-hydroxyphenyl)-1,3,5-triazine.

[0033] In an example, the weight percentage A of the characteristic group in the first surface is 20-40% (e.g., 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, or 40%).

[0034] In an example, the weight percentage A of the characteristic group in the first surface is 25-30%.

[0035] In an example, the weight percentage B of the ester group in the first surface is 1-20% (e.g., 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, or 20%).

[0036] In an example, the weight percentage B of the ester group in the first surface is 1.5-15%.

[0037] In an example, the Dv10 of the first particles is 0.01-0.5 μm (e.g., 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, or 0.5 μm).

[0038] In an example, the Dv98 of the first particles is 2-5 μm (e.g., 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm).

[0039] In an example, the Dv10 of the first particles is 0.01-0.5 μm and the Dv98 of the first particles is 2-5 μm. Controlling the Dv10 and Dv98 of the first particles can further ensure the corrosion effect of fluoroethylene carbonate on the first particles while avoiding excessive corrosion, ensuring that the corrosion effect does not affect the stability of the separator structure, further reducing the impedance of the CEI membrane, reducing the polarization phenomenon of the battery at room temperature, reducing the pressure drop of the battery fast charging, and improving the charge-discharge performance and rate performance of the battery.

[0040] In the present application, Dv10 is the particle size corresponding to 10% of the cumulative particle size distribution in the volume particle size distribution of the first particles. Dv98 is the particle size corresponding to 98% of the cumulative particle size distribution in the volume particle size distribution of the first particles. In the present application, the volume particle size distribution of the first particles can be obtained by randomly selecting 100 μm x 100 μm in the SEM image of the coating surface, and combining with the graphic analysis software (for example, ImageJ, NanoMeasurer, Matlab, etc.) to measure and statistically process to obtain Dv10 and Dv98. The Dv10 of the first particles and the Dv98 of the first particles can also be obtained by laser particle size analyzer test, for example, before preparing the separator, the first particles are measured by laser particle size analyzer to obtain the Dv10 of the first particles and the Dv98 of the first particles.

[0041] In an example, the first polymer comprises an acrylate polymer.

[0042] In an example, the monomers forming the first polymer comprise one or more of methyl methacrylate, butyl acrylate, n-propyl acrylate, octyl acrylate, ethyl methacrylate, isooctyl acrylate, stearyl acrylate, ethyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate.

[0043] In an example, the first polymer comprises at least one of polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer (for example, methyl methacrylate-acrylonitrile copolymer), acrylate-ethylene copolymer, acrylate-acrylonitrile-ethylene copolymer, copolymer of styrene-acrylate monomer-acrylonitrile, copolymer of ethylhexyl acrylate-methyl methacrylate, copolymer of butyl acrylate-methyl methacrylate, methyl acrylate-N,N-dimethyl acrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate-acrylic acid copolymer, ethyl acrylate-N,N-diethyl acrylamide copolymer, and ethyl acrylate-2-(diethylamino)ethyl acrylate.

[0044] In an example, the weight percentage of the monomer containing an ester group in the first polymer is 50%-100% (for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%).

[0045] In an example, the glass transition temperature of the first polymer is 40°C-75°C (for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, or 75°C).

[0046] In an example, the second particles are arranged in a stacked manner in the coating. It can be understood that the stacked manner refers to that in the thickness direction of the separator, the second particles are arranged in one layer or stacked in multiple layers in the coating, and no large particle size agglomerates are present. As shown in FIG. 1, the red circles enclose the second particles, and it can be understood that Figure 3 Figure 3 In the figure, only part of the second particles are marked, and all the second particles are not marked.

[0047] In an example, 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 application, the Dv95 is the particle size corresponding to the cumulative particle size distribution reaching 95% in the volume particle size distribution of the second particles. In the present application, the volume particle size distribution of the second particles can be obtained by randomly selecting 100 μm x 100 μm in the SEM image of the coating surface, and combining with the graphic analysis software (for example, ImageJ, NanoMeasurer, Matlab, etc.) to measure and statistically process to obtain the Dv95. The Dv95 of the second particles can also be obtained by laser particle size analyzer test, for example, before preparing the separator, the Dv95 of the second particles is obtained by laser particle size analyzer test.

[0048] In an example, the battery satisfies the following relationship: 1≤A / B≤30 (for example, 1, 3, 5, 8, 10, 13, 15, 18, 20, 23, 25, 28 or 30), wherein A is the weight percentage of the characteristic group in the first surface, and B is the weight percentage of the ester group in the first surface. It can be understood that A refers to the weight percentage of the characteristic group in all the elements exposed on the first surface, and B refers to the weight percentage of the ester group in all the elements exposed on the first surface, and A and B can be changed by adjusting one or more factors such as 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 percentage of the first particles in the second coating.

[0049] In an example, the battery satisfies the following relationship: 3≤A / B≤18.

[0050] According to a specific embodiment, A is 20%-40% and B is 1%-20%, and the battery satisfies the following relationship: 1≤A / B≤30.

[0051] According to a specific embodiment, A is 25%-30% and B is 1.5%-15%, and the battery satisfies the following relationship: 3≤A / B≤18. ​

[0052] In an example, the coating includes third particles, a composition of the third particles includes a fluoropolymer. As shown, Figure 3 the third particles are indicated by the yellow circles. It is understood that, Figure 3 only a portion of the third particles are indicated, not all of the third particles.

[0053] In an example, the monomer that forms the fluoropolymer includes one or more of vinylidene fluoride, tetrafluoroethylene, hexafluoroethylene, and hexafluoropropylene.

[0054] In an example, the fluoropolymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoroethylene, polyhexafluoropropylene, fluorovinylidene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0055] In an example, the third particles include primary particles and secondary particles.

[0056] In an example, the average particle size dl of the secondary particles in the third particles is 2 pm to 15 pm (e.g., 2 pm, 3 pm, 4 pm, 5 pm, 6 pm, 7 pm, 8 pm, 9 pm, 10 pm, 11 pm, 12 pm, 13 pm, 14 pm, or 15 pm).

[0057] In an example, the average particle size dl of the secondary particles in the third particles is 3 pm to 10 pm.

[0058] In an example, the average particle size of the primary particles in the third particles is 0.15 pm to 0.4 pm (e.g., 0.15 pm, 0.2 pm, 0.25 pm, 0.3 pm, 0.35 pm, or 0.4 pm).

[0059] In the present application, the secondary particles of the third particles are formed by aggregation of primary particles of the third particles, wherein the agglomerates formed by agglomeration of more than 4 primary particles are secondary particles. The average particle size of the primary particles in the third particles and the average particle size of the secondary particles can be tested 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, the smallest square or rectangle that completely surrounds the secondary particles of one third particle is drawn, that is, the square or rectangle whose edges are in contact with the edges of the secondary particles of the third particle is drawn, 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 the 10 μm*10 μm area randomly selected on the coating surface, the particle size of any 100 secondary particles of the third particle is measured, and the number average is the average particle size; the above operation is repeated 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 image, the number average of the particle size of any 100 secondary particles in the image is taken as the average particle size of the secondary particles, and when 100 secondary particles cannot be observed in the image, multiple images are taken, and the number average of the particle size of the total 100 secondary particles is taken as the average particle size. The scanning image can be obtained by observing the surface of the coating using a scanning electron microscope (Hitachi, Ltd. S-3400N). The average particle size of the primary particles in the third particles can be obtained by referring to the test method of the average particle size of the secondary particles in the third particles.

[0060] In an example, 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 units of μm, and d2 is the Dv95 of the second particles, in units of μm. Controlling the separator to satisfy the above relationship can ensure that the coating is not excessively swollen at room temperature, improve the mechanical stability of the coating at room temperature, reduce the long cycle impedance of the battery at room temperature, and improve the long cycle performance of the battery at room temperature.

[0061] In an example, the separator satisfies the following relationship: 1.5≤d1 / d2≤20.

[0062] According to a specific embodiment, d1 is 2-15, d2 is 0.5-5, and the separator satisfies the following relationship: 1≤d1 / d2≤25.

[0063] According to a specific embodiment, d1 is 3-10, d2 is 0.5-5, and the separator satisfies the following relationship: 1.5≤d1 / d2≤20.

[0064] In an example, the coating includes a first coating and a second coating, the first coating is between the substrate layer and the second coating, the first coating includes first particles, and the second coating includes second particles and optionally (the "optionally" means that it can exist or can not exist) third particles.

[0065] In an example, the thickness of the first coating is 0.2 μm-4 μm (e.g., 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, or 4 μm).

[0066] In an example, the first coating includes a binder.

[0067] In an example, the binder includes one or more of polyvinyl alcohol, styrene butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene-acrylic latex, polyacrylonitrile, polyethyl acrylate, polyvinyl acetate, polyacrylate, polyurethane polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylic acid, or a copolymer derived from the above polymers.

[0068] In an example, the weight percentage of the first particles is 90%-99% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) and the weight percentage of the binder is 1%-10% (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%) based on the total weight of the first coating.

[0069] In an example, the thickness of the second coating is 0.5 μm-5 μm (e.g., 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).

[0070] In an example, the coverage of the second coating on the surface of the first coating is 15%-50% (e.g., 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%).

[0071] In the present application, the coverage of the second coating on the surface of the first coating refers to the percentage of the area of the orthographic projection of the second coating on the first coating in the surface area of the first coating. The coverage of the second coating on the surface of the first coating can be tested by the following method: obtaining a micrograph of the surface of the separator by SEM, randomly dividing an area of 10000 µm 2The area of the second coating layer on the surface of the first coating layer is measured by the following method: a region (for example, 100 pm x 100 pm) of the surface of the first coating layer is selected, and the region is divided into 100*100 uniform squares. If the projection of the second coating layer on a square covers more than half of the area of the square, the square is considered to be occupied by the second coating layer; otherwise, the square is considered to be not occupied by the second coating layer. The number of squares occupied by the second coating layer is counted, and the total number of squares occupied by the second coating layer is recorded as X. The coverage rate of the second coating layer on the surface of the first coating layer is calculated as (X / 100*100)*100%. The above operation is repeated 5 times, and the average value of the 5 times is taken as the coverage rate of the second coating layer on the surface of the first coating layer.

[0072] In an example, the weight percentage 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%) based on the total weight of the second coating layer, and the weight percentage of the third particles is 0%-90%.

[0073] According to a specific embodiment, as shown in Figure 2 The diaphragm 1 includes a substrate layer 11 and a coating layer 12, and 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, and the first coating layer is located between the substrate layer and the second coating layer.

[0074] In an example, as shown in Figure 1 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.

[0075] In an example, the diaphragm includes a substrate layer, a coating layer, and a third coating layer, the coating layer is located on one side of the substrate layer, and the third coating layer is located on the other side of the substrate layer.

[0076] In an example, the coverage rate of the third coating layer on the surface of the substrate layer is 10%-50% (for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%). The test of the coverage rate of the third coating layer on the surface of the substrate layer can be performed according to the test method of the coverage rate of the second coating layer on the surface of the first coating layer.

[0077] In an example, the third coating layer includes fourth particles, the fourth particles are arranged in a stack in the third coating layer, and the composition of the fourth particles includes a second polymer, and the second polymer includes a polymer containing an ester group.

[0078] In the present invention, the layered arrangement of the fourth particles in the third coating layer means that the fourth particles are present in one layer or a plurality of layers in the third coating layer in the thickness direction of the separator, and that no agglomerates of large particle size are present.

[0079] In an example, the second polymer comprises an acrylate-based polymer.

[0080] In an example, the monomer forming the second polymer comprises one or more of methyl methacrylate, butyl acrylate, n-propyl acrylate, octyl acrylate, ethyl methacrylate, isooctyl acrylate, stearyl acrylate, ethyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate.

[0081] In an example, the second polymer comprises at least one of polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer (e.g., methyl methacrylate-acrylonitrile copolymer), acrylate-acrylonitrile-ethylene copolymer, copolymer of styrene-acrylate monomer-acrylonitrile, copolymer of ethylhexyl acrylate-methyl methacrylate, copolymer of butyl acrylate-methyl methacrylate, methyl acrylate-N,N-dimethyl acrylamide copolymer, ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethyl acrylamide copolymer, and ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate.

[0082] In the present invention, the first polymer and the second polymer can be the same or different.

[0083] In an example, the third coating layer is the same as or different from the second coating layer. Specifically, one or more of 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 can be the same or different.

[0084] In an 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 can be the same or different.

[0085] In an example, the thickness of the substrate layer is 2 μm-10 μm (e.g., 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm).

[0086] In an example, the porosity of the substrate layer is 25%-70% (e.g., 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%).

[0087] In an example, the base material layer includes 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 paraphenylene terephthalamide, or poly-m-phenylene isophthalamide, or a derivative of the above polymers.

[0088] In an example, the weight percentage of the fluorinated ethylene carbonate in the electrolyte is 15-35%.

[0089] In an example, the electrolyte includes a cyclic carbonate. The cyclic carbonate refers to a cyclic carbonate other than fluorinated ethylene carbonate.

[0090] In an example, the cyclic carbonate includes ethylene carbonate and / or propylene carbonate.

[0091] In an example, the weight percentage of the cyclic carbonate in the electrolyte is 5-50% (e.g., 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%).

[0092] In an example, the weight percentage of the cyclic carbonate in the electrolyte is 10-25%.

[0093] In an example, the ratio of the weight of the cyclic carbonate to the weight of the fluorinated ethylene 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 ratio of the weight of the cyclic carbonate to the weight of the fluorinated ethylene carbonate in 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 separator. When the ratio of the weight of the cyclic carbonate to the weight of the fluorinated ethylene carbonate is less than 0.2:1, the content of FEC in the electrolyte is too high or the content of the cyclic carbonate is too low, which can cause excessive corrosion of the coating by FEC, resulting in poor mechanical stability of the coating and reduced mechanical strength of the separator structure, which is not conducive to high-temperature bonding and high-temperature voltage drop of the battery. When the ratio of the weight of the cyclic carbonate to the weight of the fluorinated ethylene carbonate is greater than 1.5:1, the content of FEC in the electrolyte is too low or the content of the cyclic carbonate is too high, which can weaken the corrosion effect of FEC on the coating, which is not conducive to reducing the impedance of the CEI membrane and improving the flexibility of the CEI membrane, increasing the fast-charging voltage drop, and excessive swelling of the cyclic carbonate to the second particles, which reduces the lithium ion permeability of the separator and is not conducive to improving the charge-discharge performance and reducing the rate performance of the battery.

[0094] In one example, the ratio of the weight of the cyclic carbonate to the weight of the fluoroethylene carbonate is (0.6-1.1):1.

[0095] According to one specific embodiment, the weight percentage of the fluoroethylene carbonate in the electrolyte is 13%-50%, the weight percentage of the cyclic carbonate in the electrolyte is 5%-50%, and the ratio of the weight of the cyclic carbonate to the weight of the fluoroethylene carbonate is (0.2-1.5):1.

[0096] According to one specific embodiment, the weight percentage of the fluoroethylene carbonate in the electrolyte is 15%-35%, the weight percentage of the cyclic carbonate in the electrolyte is 10%-25%, and the ratio of the weight of the cyclic carbonate to the weight of the fluoroethylene carbonate is (0.6-1.1):1.

[0097] In one example, the electrolyte includes lithium hexafluorophosphate, an organic solvent, and an additive.

[0098] 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), and ethyl propionate (EP), propyl propionate (PP), ethyl butyrate, propyl acetate, ethyl difluoroacetate.

[0099] In one example, the additive includes a negative electrode surface film-forming additive, a positive electrode surface film-forming additive, and a positive and negative electrode current collector surface film-forming additive. The additive can also include an additive that can improve certain performance of the battery, such as an additive that improves overcharge performance of the battery, an additive that improves high or low temperature performance of the battery, etc. The additive can be one or more of a dinitrile compound, a trinitrile compound, etc., a lithium salt additive, a fluoro-chain carbonate, a fluoro-carboxylic acid ester, a sulfur-containing compound.

[0100] Nitrile compounds include, but are not limited to, one or more of butanedinitrile, pentanedinitrile, hexanedinitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 1,8-dicyanoctane, 1,9-dicyanononane, tetramethyl butanedinitrile, 2-methyl pentanedinitrile, 2,4-dimethyl pentanenitrile, 2,2,4,4-tetramethyl pentanedinitrile, 1,5-dicyanopentane, 2,6-dicyanoheptane, 2,7-dicyanoctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 3,5-dioxa-heptanedinitrile, 1,4-bis(cyanoethoxy)butane, ethylene glycol bis(2-cyanoethyl) ether, diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, 3,6,9,12,15,18-hexaoxaicosanedinitrile, 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.

[0101] Trinitrile compounds include, but are not limited to, one or more of 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 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.

[0102] Lithium salt additives include, but are not limited to, one or more of lithium bistrifluoromethylsulfonimide, lithium bisfluorosulfonimide salt, lithium difluorophosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorobisoxalate phosphate.

[0103] Sulfur-containing compounds include, but are not limited to, one or more of 1,3-propane sulfone, ethylene sulfate, cyclic sulfate, chain sulfate, chain sulfonate, cyclic sulfonate, cyclic sulfite, chain sulfone, cyclic sulfone.

[0104] 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, or bis(trifluoroethyl) carbonate.

[0105] In an example, the lithium hexafluorophosphate has a weight percentage of 5-30% (e.g., 5%, 10%, 15%, 20%, 25%, or 30%) based on the total weight of the electrolyte, the organic solvent has a weight percentage of 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%) based on the total weight of the electrolyte, and the additive has a weight percentage of 0-20% (e.g., 0, 0.1%, 0.5%, 1%, 5%, 10%, 15%, or 20%) based on the total weight of the electrolyte. When the weight percentage of the organic solvent in the electrolyte is 0, it means that there is no organic solvent in the electrolyte. When the weight percentage of the additive in the electrolyte is 0%, it means that there is no additive in the electrolyte.

[0106] In an 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.

[0107] In an example, the positive electrode active layer includes a positive electrode conductive agent and a positive electrode binder.

[0108] In an example, the positive electrode conductive agent includes one or more of conductive carbon black, carbon nanotube, conductive graphite, and graphene.

[0109] In an example, the positive electrode binder includes one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, acrylate-based polymer, acrylic polymer, polytetrafluoroethylene, polyacrylonitrile, polyimide, acrylate-acrylonitrile copolymer, butadiene styrene rubber, and styrene propylene rubber.

[0110] In an example, the positive electrode active material has a weight percentage of 90-99% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) based on the total weight of the positive electrode active layer, the positive electrode conductive agent has a weight percentage of 0.5-5% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%) based on the total weight of the positive electrode active layer, and the positive electrode binder has a weight percentage of 0.5-5% based on the total weight of the positive electrode active layer.

[0111] In an example, the battery has a charge cut-off voltage greater than or equal to 4.5 V.

[0112] In an example, the battery is a lithium ion secondary battery.

[0113] The application will be described in detail below through examples. The examples described in the application are only part of the examples of the application, not all examples. Based on the examples in the application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0114] The following examples are used to illustrate the battery of the application.

[0115] Example 1

[0116] (1) Separator

[0117] The first particles (melamine cyanurate (MCA), the characteristic group is triazine ring), the adhesive (polyacrylic acid) and deionized water are mixed, and after sufficient stirring, a first slurry with a solid content of 25% is obtained, and the MCA: polyacrylic acid (weight ratio) = 98%: 2% based on 100% solid mass of the slurry. The first slurry is coated on one side surface of the substrate layer (PE) by a gravure roll, dried to form a first coating layer after passing through a 60°C multi-section oven, and the thickness of the first coating layer is 1.5 μm. The second particles (methyl methacrylate-acrylonitrile copolymer) and the third particles (PVDF-HFP copolymer) are dispersed in deionized water (the weight ratio of the second particles to the third particles is 50%: 50%), and after sufficient stirring, a second slurry with a solid content of 10% is obtained. The second slurry is coated on the surface of the first coating layer by a gravure roll, dried to form a second coating layer (thickness of 0.7 μm) after passing through a 60°C multi-section oven. The fourth particles (methyl methacrylate-acrylonitrile copolymer) are dispersed in deionized water, and after sufficient stirring, a third slurry with a solid content of 10% is obtained. The third slurry is coated on the surface of the other side of the substrate layer by a gravure roll, dried to form a third coating layer after passing through a 60°C multi-section oven.

[0118] In the first surface, the number of the primary particles with a particle size less than or equal to 0.3 μm accounts for 2.1% of the total number of the primary particles in any 100 μm x 100 μm area of the first surface; the weight ratio A of the characteristic group in the first surface is 28.3%, the weight ratio B of the ester group in the first surface is 4.1%, the Dv10 of the first particles is 0.3 μm, the Dv98 of the first particles is 3.8 μm, the Dv95 of the second particles is 0.8 μm, the average particle size d1 of the secondary particles in the third particles is 6.4 μm, d1 / d2 = 6.4 / 0.8 = 8, the coverage of the second coating layer on the surface of the first coating layer is 23%, and the coverage of the third coating layer on the surface of the substrate layer is 15%.

[0119] (2) Electrolyte

[0120] In an argon-filled glove box (moisture <1 ppm, oxygen <1 ppm), ethylene carbonate, propylene carbonate, propyl propionate, ethyl propionate solvent was mixed into a uniform solvent, LiPF6, 1,3,6-hexanetricarbonitrile, fluoroethylene carbonate was slowly added, and the electrolyte was obtained after stirring uniformly. In the electrolyte, the weight percentage of LiPF6 was 20%, the weight percentage of 1,3,6-hexanetricarbonitrile was 3%, the weight percentage of fluoroethylene carbonate was 25%, the weight percentage 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.

[0121] (3) Positive electrode sheet

[0122] The positive electrode active material (lithium cobaltate), the positive electrode binder (polyvinylidene fluoride (PVDF500)), and the positive electrode conductive agent (Super P: carbon nanotube (weight ratio) = 2:1) were mixed in an N-methyl pyrrolidone (NMP) solvent in a weight ratio of 98:2:2, and continuously stirred into a uniform and flowing positive electrode slurry under the action of a stirrer. Subsequently, the positive electrode slurry was coated on both sides of an aluminum foil with a thickness of 10 μm to form a positive electrode active layer, and was sent into a 120°C vacuum oven for drying for 6 h, and then was subjected to rolling, slitting, to obtain a positive electrode sheet.

[0123] (4) Negative electrode sheet

[0124] The graphite, silicon carbon (Dv50 = 7 μm), conductive material (carbon black: carbon nanotube = 1:1), carboxymethyl cellulose sodium (CMC), and butadiene rubber were mixed in an aqueous solvent in a weight ratio of 92:6:1:0.5:0.5, and continuously stirred into a uniform and flowing negative electrode slurry under the action of a stirrer. Subsequently, the slurry was coated on both sides of a current collector copper foil with a thickness of 10 μm, and was sent into a 120°C vacuum oven for drying for 6 h, and then was subjected to rolling, slitting, to obtain a negative electrode sheet.

[0125] (5) Lithium ion battery

[0126] The positive electrode sheet prepared in step (3), the separator prepared in step (1), and the negative electrode sheet prepared in step (4) were prepared into a bare cell by winding; then the bare cell was placed in an aluminum plastic film, the electrolyte prepared in step (2) was injected into the dried bare cell, and the lithium ion battery was obtained after vacuum packaging, room temperature standing, high temperature formation, and other processes.

[0127] Example 2 group

[0128] This group of examples is used to illustrate the effect when the proportion of the number of primary particles having a particle size of less than or equal to 0.3 μm in the number of primary particles is changed within any 100 μm x 100 μm area of the first surface.

[0129] Example 2a

[0130] Example 1 was followed except that the proportion of the number of primary particles having a particle size of less than or equal to 0.3 μm in the number of primary particles was 0.03% within any 100 μm x 100 μm area of the first surface.

[0131] Example 2b

[0132] Example 1 was followed except that the proportion of the number of primary particles having a particle size of less than or equal to 0.3 μm in the number of primary particles was 3.91% within any 100 μm x 100 μm area of the first surface.

[0133] Example 3 group

[0134] This group of examples is used to illustrate the effect when the coverage of the second coating on the surface of the first coating is changed.

[0135] Example 3a

[0136] Example 1 was followed except that the coverage of the second coating on the surface of the first coating was 15.2%.

[0137] Example 3b

[0138] Example 1 was followed except that the coverage of the second coating on the surface of the first coating was 35.7%.

[0139] Example 3c

[0140] Example 1 was followed except that the coverage of the second coating on the surface of the first coating was 50%.

[0141] Example 3d

[0142] Example 1 was followed except that the coverage of the second coating on the surface of the first coating was 10.9%.

[0143] Example 3e

[0144] Example 1 was followed except that the coverage of the second coating on the surface of the first coating was 52.1%.

[0145] Example 4 group

[0146] This set of examples is used to illustrate the effect when the Dv10 and / or Dv98 of the first particles is changed.

[0147] Example 4a

[0148] Example 1 was followed except that the Dv10 of the first particles was 0.02 μm and the Dv98 of the first particles was 2.2 μm.

[0149] Example 4b

[0150] Example 1 was followed except that the Dv10 of the first particles was 0.48 μm and the Dv98 of the first particles was 4.9 μm.

[0151] Example 4c

[0152] Example 1 was followed except that the Dv10 of the first particles was 0.55 μm and the Dv98 of the first particles was 5.2 μm.

[0153] Example 5 set

[0154] This set of examples is used to illustrate the effect when d1 / d2 is changed.

[0155] Example 5a

[0156] Example 1 was followed except that the average particle size d1 of the secondary particles in the third particles was 10 μm and the Dv95 of the second particles was 0.53, d1 / d2 = 10 / 0.53 = 18.9.

[0157] Example 5b

[0158] Example 1 was followed except that the average particle size d1 of the secondary particles in the third particles was 5.5 μm and the Dv95 of the second particles was 4.91, d1 / d2 = 5.5 / 4.91 = 1.1.

[0159] Example 5c

[0160] Example 1 was followed except that the average particle size d1 of the secondary particles in the third particles was 13.2 μm and the Dv95 of the second particles was 0.53, d1 / d2 = 13.2 / 0.53 = 24.9.

[0161] Example 5d

[0162] Example 1 was followed except that the average particle size d1 of the secondary particles in the third particles was 3.1 μm and the Dv95 of the second particles was 1.9, d1 / d2 = 3.1 / 1.9 = 1.6.

[0163] Example 5e

[0164] Example 1 was followed except that the average particle size dl of the secondary particles in the third particles was 14.5 μm and the Dv95 of the second particles was 0.53, dl / d2 = 14.5 / 0.53 = 27.4.

[0165] Example 5f

[0166] Example 1 was followed except that the average particle size dl of the secondary particles in the third particles was 2.2 μm and the Dv95 of the second particles was 2.4, dl / d2 = 2.2 / 2.4 = 0.9.

[0167] Example 6 group

[0168] This group of examples was used to show the effect when the weight ratio of the cyclic carbonate to the fluoroethylene carbonate in the electrolyte was changed.

[0169] Example 6a

[0170] Example 1 was followed except that the weight ratio of the fluoroethylene carbonate in the electrolyte was 13% and the weight ratio of the cyclic carbonate to the fluoroethylene carbonate was 1.38.

[0171] Example 6b

[0172] Example 1 was followed except that the weight ratio of the fluoroethylene carbonate in the electrolyte was 15% and the weight ratio of the cyclic carbonate to the fluoroethylene carbonate was 1.2.

[0173] Example 6c

[0174] Example 1 was followed except that the weight ratio of the fluoroethylene carbonate in the electrolyte was 35% and the weight ratio of the cyclic carbonate to the fluoroethylene carbonate was 0.51.

[0175] Example 6d

[0176] Example 1 was followed except that the weight ratio of the fluoroethylene carbonate in the electrolyte was 50% and the weight ratio of the cyclic carbonate to the fluoroethylene carbonate was 0.36.

[0177] Example 7 group

[0178] This group of examples was used to show the effect when the weight ratio of the cyclic carbonate to the fluoroethylene carbonate in the electrolyte was changed.

[0179] Example 7a

[0180] Example 1 was followed except that the weight ratio of the cyclic carbonate in the electrolyte was 5% and the weight ratio of the cyclic carbonate to the fluoroethylene carbonate was 0.2.

[0181] Example 7b

[0182] Example 7b was conducted as in Example 1, except that the weight percentage of the cyclic carbonate in the electrolyte was 10%, and the ratio of the weight of the cyclic carbonate to the weight of the fluoroethylene carbonate was 0.4.

[0183] Example 7c

[0184] Example 7c was conducted as in Example 1, except that the weight percentage 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.

[0185] Example 7d

[0186] Example 7d was conducted as in Example 1, except that the weight percentage of the cyclic carbonate in the electrolyte was 37%, and the ratio of the weight of the cyclic carbonate to the weight of the fluoroethylene carbonate was 1.48.

[0187] Example 7e

[0188] Example 7e was conducted as in Example 1, except that the weight percentage of the fluoroethylene carbonate in the electrolyte was 31%, the weight percentage of the cyclic carbonate in the electrolyte was 50%, the ratio of the weight of the cyclic carbonate to the weight of the fluoroethylene carbonate was 1.61, the weight percentage of LiPF6 in the electrolyte was 18%, the weight percentage of 1,3,6-hexanetricarbonitrile in the electrolyte was 1%, and the electrolyte was free of propyl propionate and ethyl propionate.

[0189] Example 7f

[0190] Example 7f was conducted as in Example 1, except that the weight percentage of the fluoroethylene carbonate in the electrolyte was 50%, the weight percentage of the cyclic carbonate in the electrolyte was 5%, and the ratio of the weight of the cyclic carbonate to the weight of the fluoroethylene carbonate was 0.1.

[0191] Example 8 group

[0192] This group of examples was used to illustrate the effect when the composition of the first particles was changed.

[0193] Example 8a

[0194] Example 8a was conducted as in Example 1, except that the composition of the first particles was uracil.

[0195] Example 8b

[0196] Example 8b was conducted as in Example 1, except that the composition of the first particles was aluminum diethylphosphinate.

[0197] Example 8c

[0198] Example 1 was followed except that the first particle was composed of melamine tris thiocyanate.

[0199] Example 8d

[0200] Example 1 was followed except that the first particle was composed of cytosine.

[0201] Example 9 group

[0202] This group of examples is intended to illustrate the effect of changing the composition of the second particle.

[0203] Example 9a

[0204] Example 1 was followed except that the second particle was composed of acrylic acid-ethylene copolymer.

[0205] Example 9b

[0206] Example 1 was followed except that the second particle was composed of PMMA.

[0207] Example 10 group

[0208] This group of examples is intended to illustrate the effect of changing the composition of the third particle.

[0209] Example 10a

[0210] Example 1 was followed except that the third particle was composed of PVDF.

[0211] Example 10b

[0212] Example 1 was followed except that the third particle was composed of polyvinyl fluoride.

[0213] Example 11 group

[0214] This group of examples is intended to illustrate the effect of changing the specific selection of cyclic ethylene carbonate.

[0215] Example 11a

[0216] Example 1 was followed except that the cyclic ethylene carbonate was all EC.

[0217] Example 11b

[0218] Example 1 was followed except that the cyclic ethylene carbonate was all PC.

[0219] Example 12

[0220] The procedure of Example 1 was followed except that the first slurry was coated on both sides of the substrate layer to form the first coating layer, the second slurry was coated on both sides of the first coating layer to form the second coating layer, and the separator did not include a third coating layer.

[0221] Example 13

[0222] The procedure of Example 1 was followed except that the first particles (melamine cyanurate (MCA), characteristic group is triazine ring), the binder (polyacrylic acid), the second particles (methyl methacrylate-acrylonitrile copolymer), the third particles (PVDF-HFP copolymer) and deionized water were mixed, and after sufficient stirring, a coating slurry with a solid content of 15% was obtained, wherein the first particles: second particles: third particles: binder (weight ratio) = 85:8:6:1. The coating slurry was coated on one side of the substrate layer by means of a gravure roll, dried after passing through a multi-section oven at 60°C to form a coating layer. The third slurry was coated on the other side of the substrate layer by means of a gravure roll, dried after passing through a multi-section oven at 60°C to form a third coating layer.

[0223] Example 14

[0224] The procedure of Example 1 was followed except that the third particles were not present.

[0225] Comparative Example 1

[0226] The procedure of Example 1 was followed except that the first particles were composed of alumina.

[0227] Comparative Example 2

[0228] The procedure of Example 1 was followed except that the first particles were composed of polyimide.

[0229] Comparative Example 3

[0230] The procedure of Example 1 was followed except that, within any 100 μm x 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 accounted for 0% of the number of the primary particles.

[0231] Comparative Example 4

[0232] The procedure of Example 1 was followed except that, within any 100 μm x 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 accounted for 4.3% of the number of the primary particles.

[0233] Comparative Example 5

[0234] The procedure of Example 1 was followed except that the weight percentage of fluoroethylene carbonate in the electrolyte was 12%, and the ratio of the weight of cyclic carbonate to the weight of fluoroethylene carbonate was 1.5.

[0235] Comparative Example 6

[0236] Refer to Example 1, except that the weight percentage of fluoroethylene carbonate in the electrolyte is 11.2%, and the ratio of the weight of cyclic carbonate to the weight of fluoroethylene carbonate is 0.35.

[0237] Test Example

[0238] The lithium ion batteries prepared from the examples and comparative examples were respectively tested as follows:

[0239] 1. Battery polarization

[0240] The resistance R1 was measured by applying a 10-second discharge pulse at 2.5C at 100% state of charge (SOC) at 25°C, the resistance R2 was measured by applying a 10-second discharge pulse at 2.5C at 50% state of charge (SOC) at 25°C, and the battery polarization AR = R1 - R2.

[0241] 2. Fast-charging voltage drop test

[0242] At 25°C, the lithium ion battery was charged at 3C constant current to a voltage of 4.5V, then charged at 4.5V constant voltage to a current of 0.05C, and then discharged at 1C constant current to a voltage of 3.0V. After standing for 5 minutes, the voltage was tested and recorded as the pre-storage voltage. Then it was stored at -20°C for 24 hours, and the voltage was retested and recorded as the post-storage voltage. The voltage drop = pre-storage voltage - post-storage voltage.

[0243] 3. Normal temperature long cycle impedance change rate test

[0244] The lithium ion battery was transferred to a 25°C environment and stood for 30 min, then discharged at 0.2C constant current to 3.0V, stood for 5 min, then charged to 4.5V at 0.5C, then constant voltage charged to the cutoff current 0.05C, stood for 5 min, and the initial full state impedance value R1 was tested using an electrochemical workstation. Then it was discharged at 0.7C constant current to 3.0V, and then cycled 1000T according to the following steps: 0.5C charging to 4.5V, then constant voltage charging to the cutoff current 0.05C, standing for 5 min, 0.7C constant current discharging to 3.0V. After the cycle was completed, 0.5C charging to 4.5V, then constant voltage charging to the cutoff current 0.05C, standing for 5 min, and the full state impedance value R2 after the cycle was tested using an electrochemical workstation. The change rate was calculated as follows: [(R2-R1) / R1] x 100%.

[0245] 4. Normal temperature long cycle capacity retention rate test

[0246] 25℃±2℃ environment, 0.7C constant current constant voltage charging to the upper limit voltage 4.5V, cut-off 0.05C, record the initial thickness P0, then 0.2C constant current discharge to the lower limit voltage 3.0V, the initial discharge capacity is recorded as C0, static 10min, cycle mode: 3C constant current constant voltage charging to 4.25V, cut-off 2C, turn 2C constant current constant voltage charging to 4.48V, cut-off 1.5C, turn 1.5C constant current constant voltage charging to the upper limit voltage 4.5V, cut-off 0.18C, static 5min, 0.7C discharge to the lower limit voltage 3.0V. After 1000T cycles, 0.7C constant current constant voltage charging to the upper limit voltage, cut-off 0.05C, record the final thickness P1, then 0.2C constant current discharge to the lower limit voltage, the initial discharge capacity is recorded as C1.

[0247] Capacity retention rate: C=C1 / C0*100%

[0248] 5. Normal temperature cycle impedance

[0249] The lithium ion battery is transferred to a 25℃ environment, and is allowed to stand for 30min. Then, it is discharged at a constant current of 0.2C to 3.0V, and is allowed to stand for 5min. Then, it is charged at a constant current of 0.5C to 4.5V, and is then charged at a constant voltage until the cut-off current is 0.05C. After being allowed to stand for 5min, it is discharged at a constant current of 0.7C to 3.0V. Then, it is cycled for 10T according to the following steps: charging at a constant current of 0.5C to 4.5V, and then charging at a constant voltage until the cut-off current is 0.05C. After being allowed to stand for 5min, it is discharged at a constant current of 0.7C to 3.0V. After the cycle is completed, it is charged at a constant current of 0.5C to 4.5V, and is then charged at a constant voltage until the cut-off current is 0.05C. After being allowed to stand for 5min, the full-charge state impedance value R1 after the cycle is measured using an electrochemical workstation.

[0250] 6. 45℃ rate performance

[0251] The lithium ion battery is allowed to stand at 45±2℃ for 60min, and is discharged at a constant current of 0.2C to 3.0V. After being allowed to stand for 10min, it is charged at a constant current of 1.2C to 4.5V, and is then charged at a constant voltage until the cut-off current is 0.05C. After being allowed to stand for 10min, it is discharged at a constant current of 1C to 3.0V. After being allowed to stand for 10min, the discharge capacity at this time is recorded as Q0. Then, it is charged at a constant current of 2.5C to 4.5V, and is then charged at a constant voltage until the cut-off current is 0.05C. After being allowed to stand for 10min, it is discharged at a constant current of 1C to 3.0V. After being allowed to stand for 10min, the discharge capacity at this time is recorded as Q2. The capacity retention rate is (Q2 / Q0)×100%.

[0252] 7. High-temperature storage internal resistance change rate

[0253] The lithium ion battery was charged at 3C constant current to 4.5V at 60℃, then charged at 4.5V constant voltage to 0.05C, and then discharged at 1C constant current to 3.0V, and then rested for 5 minutes, and then the resistance was tested, and recorded as the pre-storage resistance R1. Then stored at 60℃ for 7 days, and then retested the resistance, and recorded as the post-storage resistance R2. The storage resistance change rate was: [(R2-R1) / R1]x100%.

[0254] The results obtained are recorded in Table 1.

[0255] Table 1

[0256]

[0257]

[0258] As can be seen from Table 1, by comparing the comparative examples and the examples, the impedance difference between 100% SOC and 50% SOC of the battery of the examples is significantly reduced, the room temperature cycle impedance is reduced, the room temperature cycle impedance change rate is reduced, the room 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 resistance change rate is significantly reduced, indicating that the number of primary particles with a particle size less than or equal to 0.3 μm in the second particles in the unit area of the coating surface and the weight percentage of fluoroethylene carbonate in the electrolyte are controlled, which reduces the cycle impedance of the battery and improves the long cycle performance and rate performance of the battery.

[0259] The preferred embodiments of the application are described in detail above, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the application and fall within the protection scope of the application.

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 first polymer includes an acrylic 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 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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