Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, the negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer comprises a negative electrode active material. The coating weight of the positive electrode active material layer is Wz, the coating weight of the negative electrode active material layer is Wf, and Wz and Wf satisfy: 1.6Wf≤Wz≤2.2Wf and 3.25mg / cm2≤Wf≤5.84mg / cm2. Dv99 of the positive electrode active material is 27 μm to 33 μm, and Dv99 of the negative electrode active material is 23 μm to 28 μm. The separator comprises a separator substrate, a first bonding coating, and a second bonding coating, wherein the first bonding coating comprises a first polymer binder, the average particle size of the first polymer binder is 0.3 μm to 3 μm, the second bonding coating comprises a second polymer binder, and the average particle size of the second polymer binder is 10 μm to 38 μm. By means of the configurations, the cycle performance and high-temperature stability of the secondary battery can be improved.

Description

Secondary battery and power-consuming device Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electrical device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have the characteristics of high specific energy, high operating voltage, low self-discharge rate, small size and light weight, and are widely used in various fields such as energy storage, portable electronic devices and electric vehicles. With the continuous iterative development of consumer lithium-ion batteries in recent years, the market demand for their charging speed has become increasingly higher. The proportion of fast-charging products has gradually increased, and the charging rate has continued to increase. Consumer demand has gradually increased from 1C to 3C, 5C, 6C, 7C and 10C. At a rate of 10C, a lithium-ion battery can be fully charged in less than 15 minutes, which brings a very good user experience and provides great convenience in daily life. However, in order to meet the requirements of high-rate charging and cycling, the high-temperature stability of lithium-ion batteries is affected. This is because under high-rate charging and high-temperature conditions (for example, temperatures greater than or equal to 40°C), side reactions in lithium-ion batteries increase. Therefore, how to strike a balance between the cycling performance and high-temperature stability of fast-charging lithium-ion batteries has become a technical problem that needs to be solved urgently by those skilled in the art.

[0003] Summary of the Invention

[0004] The purpose of the present application is to provide a secondary battery that takes into account both the cycle performance and high-temperature storage performance of the secondary battery, and at the same time provides an electrical device using the secondary battery.

[0005] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application. However, the secondary batteries of this application are not limited to lithium-ion batteries, but can also be applied to secondary batteries such as sodium-ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a secondary battery, which includes an electrode assembly, the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material. The coating weight of the positive electrode active material layer is W z , the coating weight of the negative electrode active material layer is W f , W z and W f Between: 1.6W f ≤W z ≤2.2W f 、3.25mg / cm 2 ≤W f≤5.84mg / cm 2 . The Dv99 of the positive electrode active material is 27μm to 33μm, preferably 28μm to 31μm, and the Dv99 of the negative electrode active material is 23μm to 28μm, preferably 24μm to 26μm. The isolation membrane includes an isolation membrane substrate, a first bonding coating and a second bonding coating, and the first bonding coating and the second bonding coating are respectively arranged on both sides of the isolation membrane substrate; the first bonding coating includes a first polymer binder, and the average particle size of the first polymer binder is 0.3μm to 3μm; the second bonding coating includes a second polymer binder, and the average particle size of the second polymer binder is 10μm to 38μm.

[0007] The present application controls the Dv99 of the positive electrode active material and the negative electrode active material within the above range, so that the lithium ions have a shorter transmission path inside the positive electrode active material and the negative electrode active material during the transmission process, and have a smaller transmission tortuosity inside the positive electrode sheet and the negative electrode sheet, so as to reduce the concentration polarization of the secondary battery, thereby making the secondary battery have good cycle performance. The present application controls the coating weight of the positive electrode active material layer and the negative electrode active material layer within the above range, which can shorten the transmission distance of lithium ions and electrons inside the positive electrode sheet and the negative electrode sheet, thereby reducing the ohmic polarization and concentration polarization of the secondary battery and accelerating the infiltration of the positive electrode sheet and the negative electrode sheet by the electrolyte. However, the high activity design of small-particle positive electrode active material, small-particle negative electrode active material and low coating weight of the positive electrode active material layer and the negative electrode active material layer makes it easy for side reactions to occur between the positive electrode active material, the negative electrode active material and the electrolyte, especially at high temperatures, violent side reactions occur to produce a large amount of gas, which makes the high temperature performance of the lithium-ion battery poor. In the present application, a first bonding coating and a second bonding coating are respectively provided on both sides of the isolation membrane, and the average particle size of the first polymer binder in the first bonding coating and the average particle size of the second polymer binder in the second bonding coating are within the above-mentioned range of the present application, which is beneficial to strengthening the interface between the isolation membrane and the electrode, inhibiting gas production under high temperature conditions, and improving the cycle performance and high-temperature storage performance. On one side of the second bonding coating of the isolation membrane, an electrolyte flow channel can be generated and the electrolyte can be stored, meeting the requirements of the secondary battery for high electrolyte retention (such as 1.5g / Ah to 2.4g / Ah) and high transmission and infiltration in the fast charging state, thereby ensuring the battery rate and cycle performance.

[0008] This application combines the adhesive layers on both sides of the isolation membrane, the Dv99 of the positive electrode active material, the Dv99 of the negative electrode active material, the coating weight of the positive electrode active material layer and the coating weight of the negative electrode active material layer, so that there is a good synergistic effect between the three, which can improve the cycle performance of the secondary battery while taking into account the high temperature stability of the secondary battery.

[0009] In one embodiment of the present application, the first bonding coating is arranged on the side of the separator substrate close to the negative electrode sheet, and the second bonding coating is arranged on the side of the separator substrate close to the positive electrode sheet. By setting the positional relationship between the first bonding coating and the second bonding coating in the separator and the negative electrode sheet and the positive electrode sheet, the secondary battery can further improve its cycle performance on the basis of having good high-temperature stability. At the same time, for most secondary batteries, fast charging is mainly required for energy replenishment, but there is no need for fast discharge, that is, the charging rate is much greater than the discharge rate. The secondary battery charging process mainly involves the embedding of lithium ions in the negative electrode. Therefore, setting the first bonding coating with smaller separator particles on the negative electrode sheet side can shorten the lithium ion transmission path during charging and achieve faster charging speed.

[0010] In one embodiment of the present application, the Dv50 of the positive electrode active material is 10 μm to 15 μm, preferably 11 μm to 13 μm, and the Dv50 of the negative electrode active material is 7 μm to 12 μm, preferably 8 μm to 11 μm. Regulating the Dv50 of the positive and negative electrode active materials within the above ranges is beneficial for achieving a secondary battery with high energy density while maintaining good cycle and high-temperature stability.

[0011] In one embodiment of the present application, 6.49 mg / cm 2 ≤W z ≤11.69mg / cm 2 By regulating the coating weight of the positive electrode active material layer within the scope of this application, while taking into account the processing performance and energy density of the secondary battery, the transmission distance of lithium ions and electrons on the positive electrode sheet is shortened, which is beneficial to reducing the impedance of the secondary battery and making the secondary battery have good cycle performance.

[0012] In one embodiment of the present application, the thickness of the first bonding coating is 0.2 μm to 4 μm, and the thickness of the second bonding coating is 5 μm to 20 μm. The first bonding coating has a smaller particle size and stronger bonding strength. Ensuring its thickness is between 0.2 μm and 4 μm can maximize energy density while ensuring bonding strength, while shortening the lithium ion transmission path in the active material layer corresponding to the first bonding coating. The second bonding coating has a larger particle size, which can form a channel for electrolyte circulation. Setting it between 5 μm and 20 μm can improve energy density while ensuring electrolyte flow and wettability.

[0013] In one embodiment of the present application, the single-sided coating weight of the first bonding coating is 1×10 -4 mg / mm 2 to 1×10 -3 mg / mm 2 The coating weight of the second adhesive coating on one side is 4×10 -4mg / mm 2 to 2×10 -3 mg / mm 2 Regulating the single-sided coating weight of the first bonding coating within the above range can fully utilize the high bonding properties of the first bonding coating, better bond the pole piece and the separator, and ensure the high-temperature stability and mechanical reliability of the secondary battery. Regulating the single-sided coating weight of the second bonding coating within the above range can fully realize the electrolyte flow channel between the pole piece and the separator, and improve the dynamics and cycle performance of the secondary battery.

[0014] In one embodiment of the present application, the coverage of the first polymer binder per unit area in the first bonding coating layer is 40% to 60%. By regulating the coverage of the first polymer binder per unit area in the first bonding coating layer within the above range, the high bonding properties of the first bonding coating layer can be fully utilized. When the isolation membrane is bonded to the pole piece, lithium ions have a faster transmission speed, which is more conducive to the secondary battery having good dynamic performance, so that the secondary battery has a lower production cost while taking into account both cycle performance and high temperature stability.

[0015] In one embodiment of the present application, the first polymer binder includes a core-shell structure first polymer binder or a non-core-shell structure first polymer binder, and the polymerization monomer of the core of the core-shell structure first polymer binder includes at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid or maleic acid; the polymerization monomer of the shell of the core-shell structure first polymer binder includes at least one of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, chloromethyl ethyl acrylate, chlorostyrene, fluorostyrene, methylstyrene, acrylonitrile or methacrylonitrile. The polymerization monomer of the non-core-shell structure first polymer binder includes at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, fluorostyrene, chlorostyrene or propylene. The above-mentioned first polymer binder is applied to the first bonding coating layer, which can make the first bonding coating layer have high bonding force.

[0016] In one embodiment of the present application, the coverage of the second polymer binder per unit area of ​​the second bonding coat layer is 40% to 60%. By regulating the coverage of the second polymer binder per unit area of ​​the second bonding coat layer within this range, the separator has a strong bond with the positive or negative electrode sheet, enabling the secondary battery to achieve both cycling performance and high-temperature stability while having lower production costs.

[0017] In one embodiment of the present application, the polymerizable monomers of the second polymer binder include at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, allyl chloride, acrylic acid, methyl acrylate, butyl acrylate, chlorostyrene, fluorostyrene, ethyl acrylate, ethyl methacrylate, methyl methacrylate, butyl methacrylate, ethyl chloromethylacrylate, styrene, butadiene, or acrylonitrile. The use of the aforementioned second polymer binder can provide a larger gap between the second bonding coating and the positive electrode sheet, or between the second bonding coating and the negative electrode sheet, and exhibit good bonding properties. This provides better heat dissipation during cycling, facilitates electrolyte transport, and results in good cycling performance and high-temperature stability for the secondary battery under fast-charging conditions.

[0018] In one embodiment of the present application, the second polymer binder includes a core-shell structure second polymer binder or a non-core-shell structure second polymer binder, and the shell of the core-shell structure second polymer binder includes at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, styrene, butadiene, acrylonitrile, acrylic acid, methyl acrylate or butyl acrylate; the core of the core-shell structure second polymer binder includes at least one of ethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate or ethyl chloromethyl acrylate. The monomers of the non-core-shell structure second polymer binder include at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, propylene, chlorostyrene, fluorostyrene, vinylidene chloride, vinylidene fluoride, hexafluoropropylene, vinyl chloride or chloropropylene. The selection of the above-mentioned second polymer binder can provide a large gap between the second bonding coating and the positive electrode sheet or between the second bonding coating and the negative electrode sheet and have good bonding performance, and dissipate heat well during the cycle, so that the secondary battery has good cycle performance and high temperature stability under fast charging conditions.

[0019] In one embodiment of the present application, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, a lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate. The above-mentioned positive electrode active materials have high surface activity and can enable the secondary battery to have good cycle performance while maintaining high-temperature stability.

[0020] In one embodiment of the present application, the positive electrode active material further includes a non-metallic element, wherein the non-metallic element includes at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. Including the above-mentioned non-metallic elements in the positive electrode active material can further improve the stability of the positive electrode active material. The above-mentioned elements can be added to the positive electrode active material by bulk doping or coating using a single substance or compound containing the above-mentioned elements.

[0021] In one embodiment of the present application, the negative electrode active material includes at least one of a carbon-based material, a silicon-based material, or a tin-based material. The carbon-based material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, or mesocarbon microbeads. The silicon-based material includes at least one of a silicon material, a silicon-carbon material, or a silicon-oxygen material. The tin-based material includes at least one of elemental tin, a tin alloy, or a tin oxide. These negative electrode active materials have high surface activity, enabling the secondary battery to have good cycle performance while maintaining high-temperature stability.

[0022] In one embodiment of the present application, the carbon-based material is tested by Raman with a peak intensity ratio of d peak to g peak of I d / I g Satisfy: 0.1≤I d / I g ≤1. Will satisfy the above I d / I g The application of high-value carbon-based materials in secondary batteries is beneficial to further improve the cycle performance of secondary batteries on the basis of good high-temperature stability.

[0023] The second aspect of the present application provides an electric device, which includes the secondary battery according to any one of the embodiments. Therefore, the electric device has good performance.

[0024] Beneficial effects of this application:

[0025] The present application provides a secondary battery and an electrical device. The present application optimizes the electrochemical system by combining the separator's adhesive layer, the positive electrode active material's Dv99, the negative electrode active material's Dv99, the coating weight of the positive electrode active material layer, and the coating weight of the negative electrode active material layer. This allows for good synergy between the separator, the positive electrode plate, and the negative electrode plate, resulting in a faster lithium ion transport rate in the secondary battery under a high-kinetic system. This improves the secondary battery's charging speed while also taking into account a low charging temperature rise, meeting the secondary battery's fast-charging kinetic requirements. It also improves the secondary battery's cycle performance while also taking into account the secondary battery's high-temperature stability. The electrical device of the present application has good performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0027] FIG1 is a schematic diagram showing the positional relationship between a separator and positive and negative electrode sheets according to an embodiment of the present application;

[0028] FIG2 is a schematic diagram showing the positional relationship between the separator and the positive electrode sheet and the negative electrode sheet according to another embodiment of the present application;

[0029] FIG3 is a schematic diagram of a cross-sectional structure of an isolation membrane according to an embodiment of the present application along its thickness direction;

[0030] FIG4 is a schematic diagram of a cross-sectional structure of an isolation membrane according to another embodiment of the present application along its thickness direction;

[0031] FIG5 is a schematic diagram of a cross-sectional structure of an isolation membrane according to another embodiment of the present application along its thickness direction;

[0032] FIG6 is a Raman spectrum of the negative electrode of Example 3-3.

[0033] Reference numerals: positive electrode sheet 10 ; negative electrode sheet 20 ; separator 30 ; separator substrate 31 ; first bonding coating 32 ; second bonding coating 33 ; ceramic coating 34 . DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the described examples are only a portion of the embodiments of this application, rather than all of them. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0035] It should be noted that in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries, and can also be applied to secondary batteries such as sodium-ion batteries.

[0036] The first aspect of the present application provides a secondary battery, which includes an electrode assembly, the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material. The coating weight of the positive electrode active material layer is W z , the coating weight of the negative electrode active material layer is W f , W z and W f Between: 1.6W f ≤W z ≤2.2W f 、3.25mg / cm 2 ≤W f ≤5.84mg / cm 2 For example, the coating weight W of the negative electrode active material layer is f 3.25 mg / cm 2, 3.5mg / cm 2 、3.75mg / cm 2 , 4mg / cm 2 , 4.25mg / cm 2 , 4.5mg / cm 2 , 4.75mg / cm 2 , 5mg / cm 2 , 5.25mg / cm 2 , 5.5mg / cm 2 , 5.84mg / cm 2 Or a range consisting of any two values. z 1.6W f , 1.7W f , 1.8W f , 1.9W f , 2.0W f , 2.1W f , 2.2W f Or a range consisting of any two of the values. The coating weight of the positive electrode active material layer is less than 1.6W f The coating weight of the negative electrode active material layer is too large relative to the coating weight of the positive electrode active material layer. When the potential of the secondary battery is reached, the lithium removal rate of the positive electrode increases significantly, resulting in a very high actual potential of the positive electrode and easy destruction of the structure. The positive electrode decays rapidly, resulting in the secondary battery being unable to cycle normally. The coating weight of the positive electrode active material layer is greater than 2.2W f If the coating weight of the positive electrode active material layer is too large relative to the coating weight of the negative electrode active material layer, the released lithium ions will be excessive, and the negative electrode will not be able to fully accept the released lithium ions from the positive electrode. The lithium ions cannot be properly embedded in the negative electrode sheet, which will lead to lithium deposition on the negative electrode sheet and affect the cycle dynamics performance of the secondary battery. The coating weight of the negative electrode active material layer is less than 3.25 mg / cm 2 , the energy density of the secondary battery is reduced, the service life is shortened, and it is difficult to meet the process requirements of the secondary battery; the coating weight of the negative electrode active material layer is greater than 5.84 mg / cm 2, the transmission distance of lithium ions in the positive electrode sheet and / or the negative electrode sheet increases, and the impedance of the secondary battery increases. The Dv99 of the positive electrode active material is 27μm to 33μm, preferably 28μm to 31μm, for example, the Dv99 of the positive electrode active material is 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, or a range consisting of any two values ​​therein. The Dv99 of the negative electrode active material is 23μm to 28μm, preferably 24μm to 26μm, for example, the Dv99 of the negative electrode active material is 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, or a range consisting of any two values ​​therein. The isolation film comprises an isolation film substrate, a first bonding coating and a second bonding coating, wherein the first bonding coating and the second bonding coating are respectively arranged on both sides of the isolation film substrate; the first bonding coating comprises a first polymer binder, and the average particle size of the first polymer binder is 0.3μm to 3μm. For example, the average particle size of the first polymer binder of the first bonding coating is 0.3μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm or a range consisting of any two of the numerical values. The second bonding coating comprises a second polymer binder, and the average particle size of the second polymer binder is 10μm to 38μm. For example, the average particle size of the second polymer binder of the second bonding coating is 10μm, 12μm, 15μm, 18μm, 20μm, 23μm, 25μm, 28μm, 30μm, 33μm, 35μm, 38μm or a range consisting of any two of the numerical values.

[0037] When the coating weight of the positive electrode active material layer and the negative electrode active material layer exceeds the upper limit of the range of this application, the transmission distance of lithium ions in the positive electrode sheet and / or the negative electrode sheet increases, and the impedance of the secondary battery increases. When the coating weight of the positive electrode active material layer and the negative electrode active material layer is lower than the lower limit of the range of this application, the energy density of the secondary battery decreases, the service life is reduced, and it is difficult to meet the process requirements of the secondary battery.

[0038] The Dv99 of the positive electrode active material is less than 27μm. The Dv99 of the positive electrode active material is too small, indicating that the volume particle size of the positive electrode active material particles is too small. When preparing the positive electrode slurry, the positive electrode active material particles are prone to agglomeration. In this way, the probability of the positive electrode active material being uniformly dispersed in the positive electrode slurry is extremely small, and the positive electrode active material particles in the formed positive electrode active material layer are unevenly distributed, which will affect the processing stability of the positive electrode sheet and cause uneven coating problems during the coating of the positive electrode slurry. In addition, the specific surface area of ​​the positive electrode active material particles will be too large, resulting in the positive electrode active material particles. As the number of interfaces in contact with the electrolyte increases, side reactions will intensify, especially in the high-kinetic electrolyte system of super-fast charging. The side reactions will be very violent, accelerating the consumption of electrolyte and the generation of side reaction products, and worsening the cycle performance and high-temperature stability of the secondary battery; the Dv99 of the positive electrode active material is greater than 33μm. The Dv99 of the positive electrode active material is too large, the transmission path of lithium ions inside the positive electrode active material particles is too long, and the tortuosity of transmission inside the positive electrode sheet is too large, which will lead to excessive concentration polarization inside the secondary battery, thereby increasing the internal resistance of the secondary battery and reducing the cycle performance of the secondary battery.

[0039] The Dv99 of the negative electrode active material is less than 23μm. The Dv99 of the negative electrode active material is too small, indicating that the volume particle size of the negative electrode active material particles is too small. When preparing the negative electrode slurry, the negative electrode active material particles are prone to agglomeration. In this way, the probability of the negative electrode active material being uniformly dispersed in the negative electrode slurry is extremely small, and the negative electrode active material particles in the formed negative electrode active material layer are unevenly distributed, which will affect the processing stability of the negative electrode sheet and cause uneven coating problems during the coating of the negative electrode slurry. In addition, the specific surface area of ​​the negative electrode active material particles will be too large, resulting in the negative electrode active material particles. As the number of interfaces in contact with the electrolyte increases, side reactions will intensify, especially in the high-kinetic electrolyte system of super-fast charging. The side reactions will be very violent, accelerating the consumption of electrolyte and the generation of side reaction products, and worsening the cycle performance and high-temperature stability of the secondary battery; the Dv99 of the negative electrode active material is greater than 28μm. The Dv99 of the negative electrode active material is too large, the transmission path of lithium ions inside the negative electrode active material particles is too long, and the tortuosity of transmission inside the negative electrode sheet is too large, which will lead to excessive concentration polarization inside the secondary battery, thereby increasing the internal resistance of the secondary battery and reducing the cycle performance of the secondary battery.

[0040] In this application, for ease of understanding, the separator is defined as having its width direction Y and its thickness direction Z in the unfolded state. It is understood that the length, width, and thickness directions of the positive and negative electrode sheets in the unfolded state are the same as those of the separator. As shown in Figures 1 and 2, the separator 30 includes a separator substrate 31, a first bonding coating 32, and a second bonding coating 33. The first bonding coating 32 and the second bonding coating 33 are respectively disposed on either side of the separator substrate 31, with the separator substrate 31 positioned between the first bonding coating 32 and the second bonding coating 33. The first bonding coating 32 can be located on either side of the positive electrode sheet 10 or on the side of the negative electrode sheet 20. As shown in Figure 1, the first bonding coating 32 is disposed on the side of the separator substrate 31 near the negative electrode sheet 20, and the second bonding coating 33 is disposed on the side of the separator substrate 31 near the positive electrode sheet 10. As shown in Figure 2, the first bonding coating 32 is disposed on the side of the separator substrate 31 near the positive electrode sheet 10, and the second bonding coating 33 is disposed on the side of the separator substrate 31 near the negative electrode sheet 20.

[0041] The average particle size of the first polymer binder is less than 0.3 μm. If the average particle size of the first polymer binder is too small, the particles of the first polymer binder are likely to agglomerate when preparing the first bonding coat slurry. As a result, the probability of the first polymer binder being uniformly dispersed in the first bonding coat slurry is extremely small, and the distribution of the first polymer binder in the formed first bonding coat is uneven, which will affect the adhesion of the first bonding coat. If the average particle size of the first polymer binder is greater than 3 μm, the average particle size of the first polymer binder is too large, and the gaps between the particles of the first polymer binder will be too large, which is not conducive to the cycle performance of the secondary battery. In addition, if the average particle size of the first polymer binder is too large, the thickness of the first bonding coat will increase, thereby increasing the volume of the secondary battery and causing a loss in its energy density.

[0042] The average particle size of the second polymer binder is less than 10 μm. If the average particle size of the second polymer binder is too small, the gap between the separator and the positive or negative electrode sheet will be too small, and the electrolyte transmission channel will be too narrow, which will affect the transmission of the electrolyte and thus the cycling performance and dynamic performance of the secondary battery. If the average particle size of the second polymer binder is greater than 38 μm, the average particle size of the second polymer binder will increase the thickness of the second bonding coat, thereby increasing the volume of the secondary battery and resulting in a loss of its energy density.

[0043] In general, the present application controls the Dv99 of the positive electrode active material and the negative electrode active material within the above range, so that the lithium ions have a shorter transmission path inside the positive electrode active material and the negative electrode active material during the transmission process, and have a smaller transmission tortuosity inside the positive electrode sheet and the negative electrode sheet, so as to reduce the concentration polarization of the secondary battery, thereby making the secondary battery have good cycle performance. The present application controls the coating weight of the positive electrode active material layer and the negative electrode active material layer within the above range, which can shorten the transmission distance of lithium ions and electrons inside the positive electrode sheet and the negative electrode sheet, thereby reducing the ohmic polarization and concentration polarization of the secondary battery and accelerating the infiltration of the positive electrode sheet and the negative electrode sheet by the electrolyte. However, the high activity design of small-particle positive active material, small-particle negative active material and low coating weight of the positive electrode active material layer and the negative electrode active material layer makes it easy for side reactions to occur between the positive electrode active material, the negative electrode active material and the electrolyte, especially at high temperatures, violent side reactions occur to produce a large amount of gas, which makes the high temperature performance of the lithium-ion battery poor. The present application sets a first bonding coating and a second bonding coating on both sides of the isolation membrane, and the average particle size of the first polymer binder in the first bonding coating and the average particle size of the second polymer binder in the second bonding coating are within the above-mentioned range of the present application, which is beneficial to strengthening the interface between the isolation membrane and the electrode, inhibiting gas production under high temperature conditions, and improving the cycle performance and high-temperature storage performance. On one side of the second bonding coating of the isolation membrane, an electrolyte flow channel can be generated and the electrolyte can be stored, meeting the requirements of the secondary battery for high electrolyte retention (such as 1.5g / Ah to 2.4g / Ah) and high transmission and infiltration in the fast charging state, thereby ensuring the rate and cycle performance of the battery. The present application combines the isolation membrane, the Dv99 of the positive active material, the Dv99 of the negative active material, the coating weight of the positive active material layer and the coating weight of the negative active material layer, so that the isolation membrane, the positive electrode sheet and the negative electrode sheet have good synergy, which can improve the cycle performance of the secondary battery while taking into account the high temperature stability of the secondary battery.

[0044] In this application, Dv99 represents the particle size that reaches the 99th percentile by volume, starting from the smallest particle size in a volume-based particle size distribution. The aforementioned "particles" in this application can be particles of either positive or negative electrode active material. Positive and / or negative electrode active materials of varying Dv99 can be obtained through mechanical crushing, grinding, or other methods.

[0045] In this application, the average particle size can be understood as an equivalent diameter. This application does not particularly limit the method for regulating the average particle size of the first polymer binder and the average particle size of the second polymer binder, as long as the purpose of this application can be achieved. For example, this can be achieved by directly purchasing the first polymer binder and the second polymer binder with an average particle size within the range of this application, or by crushing, grinding, or ball milling.

[0046] The secondary battery in the present application can be used under fast charging conditions, specifically, can be used at a charging rate of 5C to 15C. For example, the charging rate of the secondary battery is 5C, 8C, 10C, 12C, 15C, or a range consisting of any two of these values.

[0047] In one embodiment of the present application, a first bonding coating is disposed on the side of the separator substrate near the negative electrode sheet, and a second bonding coating is disposed on the side of the separator substrate near the positive electrode sheet. As shown in FIG1 , a first bonding coating 32 is disposed on the side of the separator substrate 31 near the negative electrode sheet 20, and a second bonding coating 33 is disposed on the side of the separator substrate 31 near the positive electrode sheet 10. By arranging the positional relationship between the first bonding coating and the second bonding coating in the separator and the negative and positive electrode sheets, the separator maintains excellent bonding properties with both the positive and negative electrodes, thereby further improving the cycling performance of the secondary battery while maintaining good high-temperature stability.

[0048] In one embodiment of the present application, the Dv50 of the positive electrode active material is 10 μm to 15 μm, preferably 11 μm to 13 μm, and the Dv50 of the negative electrode active material is 7 μm to 12 μm, preferably 8 μm to 11 μm. For example, the Dv50 of the positive electrode active material is 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range consisting of any two thereof. The Dv50 of the negative electrode active material is 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or a range consisting of any two thereof. By regulating the Dv50 of the positive electrode active material and the negative electrode active material within the above range, the risk of agglomeration of the positive electrode active material in the positive electrode slurry is low, and the risk of agglomeration of the negative electrode active material in the negative electrode slurry is low. On the basis of enabling the positive electrode active material and the negative electrode active material to play their own roles, the thickness of the positive electrode active material layer and the negative electrode active material is regulated within a suitable range to reduce the risk of energy density loss due to increased thickness, thereby helping the secondary battery to have a higher energy density on the basis of good cycle performance.

[0049] In this application, Dv50 represents the particle size at which 50% of the volume of the smallest particle size in a volume-based particle size distribution is reached. The "particles" mentioned above, as used herein, can be either positive electrode active materials or negative electrode active materials. Positive or negative electrode active materials with different Dv50 values ​​can be obtained through mechanical crushing, grinding, screening, or other methods.

[0050] In some embodiments of the present application, the positive electrode active material has a Dv10 of 2 μm to 7 μm and a Dv90 of 18 μm to 25 μm. In some embodiments of the present application, the positive electrode active material has a Dv10 of 3 μm to 6 μm and a Dv90 of 20 μm to 23 μm. In some embodiments of the present application, the negative electrode active material has a Dv10 of 3 μm to 7 μm and a Dv90 of 13 μm to 18 μm. In some embodiments of the present application, the negative electrode active material has a Dv10 of 4 μm to 6 μm and a Dv90 of 14 μm to 16 μm. For example, the Dv10 of the positive electrode active material is 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or a range consisting of any two thereof, and the Dv90 of the positive electrode active material is 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, or a range consisting of any two thereof. The Dv10 of the negative electrode active material is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or a range consisting of any two thereof, and the Dv90 of the negative electrode active material is 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or a range consisting of any two thereof. By regulating the Dv10 and Dv90 of the positive electrode active material and the negative electrode active material within the above range, the risk of agglomeration of the positive electrode active material in the positive electrode slurry is low, and the risk of agglomeration of the negative electrode active material in the negative electrode slurry is low. On the basis of enabling the positive electrode active material and the negative electrode active material to play their own roles, the thickness of the positive electrode active material layer and the negative electrode active material is regulated within a suitable range to reduce the risk of energy density loss due to increased thickness, thereby helping the secondary battery to have a higher energy density on the basis of good cycle performance.

[0051] In this application, Dv10 represents the particle size at which the volume-based particle size distribution, starting from the small particle size side, reaches 10% of the cumulative volume. Dv90 represents the particle size at which the volume-based particle size distribution, starting from the small particle size side, reaches 90% of the cumulative volume. The above-mentioned "particles" in this application can be particles of positive electrode active materials or particles of negative electrode active materials. Positive electrode active materials and / or negative electrode active materials with different Dv10 and Dv90 can be obtained by mechanical crushing, grinding, screening, etc.

[0052] In one embodiment of the present application, 6.49 mg / cm 2 ≤W z ≤11.69mg / cm 2 For example, Wz is 6.49 mg / cm 2 , 7mg / cm 2 , 7.5mg / cm 2 , 8mg / cm 2, 8.5mg / cm 2 , 9mg / cm 2 , 9.5mg / cm 2 、10mg / cm 2 、10.5mg / cm 2 、11mg / cm 2 、11.69mg / cm 2 Or a range consisting of any two of these values. By regulating the coating weight of the positive electrode active material layer within the range of this application, while taking into account the processing performance and energy density of the secondary battery, the transmission distance of lithium ions and electrons on the positive electrode sheet is shortened, which is beneficial to reducing the ohmic polarization and concentration polarization of the secondary battery, thereby reducing the impedance of the secondary battery and making the secondary battery have good cycle performance.

[0053] In one embodiment of the present application, as shown in Figures 1 and 2, the thickness H1 of the first bonding coating 32 is 0.2μm to 4μm, for example, the thickness H1 of the first bonding coating is 0.2μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm or a range consisting of any two of the values. The particle size of the first polymer binder in the first bonding coating is small, the bonding force of the first bonding coating is strong, and the thickness of the first bonding coating is regulated within the above range. The first bonding coating has a suitable thickness, which can reduce the risk of energy density loss caused by the increase in the volume of the secondary battery due to the excessive thickness while ensuring the bonding force of the first bonding coating, thereby improving the energy density of the secondary battery and shortening the transmission path of lithium ions in the active material layer corresponding to the first bonding coating. Thus, in this way, the secondary battery can have a good energy density while taking into account both cycle dynamics performance and high temperature stability.

[0054] In this application, the thickness of the first bonding coating layer and the thickness of the second bonding coating layer are obtained by observing and testing the parameters of the cross-sectional sample of the isolation membrane. This application does not particularly limit the method for preparing the cross-sectional sample of the isolation membrane, as long as it can achieve the purpose of this application. For example, the isolation membrane cross-sectional sample can be obtained by argon ion polishing or embedded sectioning.

[0055] In one embodiment of the present application, as shown in Figures 1 and 2, the thickness H2 of the second bonding coating 33 is 5μm to 20μm. For example, the thickness H2 of the second bonding coating is 5μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm or a range consisting of any two of the numerical values. The particle size of the second polymer binder in the second bonding coating is large, and a channel for electrolyte circulation can be formed. The thickness of the second bonding coating is regulated within the above range. The second bonding coating has a suitable thickness and can reduce the risk of energy density loss caused by the increase in the volume of the secondary battery due to the excessive thickness when the electrolyte has good flow wettability in the pole piece and the separator. In this way, the secondary battery can have good energy density based on both cycle dynamics performance and high temperature stability.

[0056] In one embodiment of the present application, the single-sided coating weight of the first bonding coating is 1×10 -4 mg / mm 2 to 1×10 -3 mg / mm 2 For example, the single-sided coating weight of the first bonding coating is 1×10 -4 mg / mm 2 , 2×10 -4 mg / mm 2 , 3×10 -4 mg / mm 2 , 4×10 -4 mg / mm 2 , 5×10 -4 mg / mm 2 , 6×10 -4 mg / mm 2 , 7×10 -4 mg / mm 2 , 8×10 -4 mg / mm 2 , 9×10 -4 mg / mm 2 , 1×10 -3 mg / mm 2 or a range consisting of any two of these values. By regulating the single-sided coating weight of the first bonding coating within the above range, the high bonding properties of the first bonding coating can be fully utilized, better bonding the electrode and separator, and ensuring the high-temperature stability and mechanical reliability of the secondary battery. It can also reduce the risk of energy density loss caused by an increase in the volume of the secondary battery due to excessive single-sided coating weight. Thus, the secondary battery can have good energy density while maintaining both cycle performance and high-temperature stability.

[0057] In one embodiment of the present application, the single-sided coating weight of the second bonding coating is 4×10 -4 mg / mm 2 to 2×10 -3 mg / mm 2 For example, the coating weight of the second adhesive coating layer on one side is 4×10 -4 mg / mm 2 , 5×10 -4 mg / mm 2 , 6×10 -4 mg / mm 2 , 7×10 -4 mg / mm 2 , 8×10 -4 mg / mm 2 , 9×10 -4 mg / mm 2 , 1×10 -3 mg / mm 2 , 2×10 -3 mg / mm 2 By controlling the single-side coating weight of the second adhesive coating within the above range, the electrolyte flow channel between the electrode and the separator can be fully realized, thereby improving the dynamics and cycle characteristics of the secondary battery.

[0058] In one embodiment of the present application, the coverage Cr1 of the first polymer binder in the first bonding coating per unit area is 40% to 60%. For example, the coverage of the first polymer binder in the first bonding coating per unit area is 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60% or a range consisting of any two of these values. By regulating the coverage of the first polymer binder in the first bonding coating per unit area within the above range, the secondary battery can have a lower production cost on the basis of taking into account both the cycle dynamics performance and the high temperature stability, and give full play to the high bonding properties of the first bonding coating. When it is beneficial for the isolation membrane to be bonded to the pole piece, lithium ions have a faster transmission speed, which is more conducive to making the secondary battery have good dynamic performance.

[0059] In one embodiment of the present application, the first polymer binder includes a core-shell structure first polymer binder, the core of the core-shell structure first polymer binder includes at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, or maleic acid; the shell of the core-shell structure first polymer binder includes at least one of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, ethyl chloromethylacrylate, chlorostyrene, fluorostyrene, methylstyrene, acrylonitrile, or methacrylonitrile. The above-mentioned first polymer binder is applied to the first bonding coating layer, which can make the first bonding coating layer have high bonding force, thereby improving the high-temperature storage performance of the secondary battery and improving the high-temperature stability of the secondary battery.

[0060] In one embodiment of the present application, the first polymer binder includes a non-core-shell structure first polymer binder, and the polymerized monomer of the non-core-shell structure first polymer binder includes at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, fluorostyrene, chlorostyrene, or propylene. The above-mentioned first polymer binder is applied to the first bonding coating layer, which can provide the first bonding coating layer with high adhesion, thereby improving the high-temperature storage performance of the secondary battery and enhancing the high-temperature stability of the secondary battery.

[0061] In one embodiment of the present application, the first bonding coating layer includes a first polymer binder, a thickener, an auxiliary binder and a wetting agent. The thickener is applied to the first bonding coating layer to increase the stability of the high-adhesion coating slurry and prevent the sedimentation of the components in the high-adhesion coating slurry. The auxiliary binder is applied to the first bonding coating layer to bond the first polymer binder to the isolation membrane substrate and the ceramic coating during the application of the first bonding coating slurry. The wetting agent is applied to the first bonding coating layer to reduce the surface energy of the first bonding coating slurry and prevent the first bonding coating slurry from leaking during the application process. The present application has no particular restrictions on the content of the first polymer binder, thickener, auxiliary binder and wetting agent in the first bonding coating layer, as long as the purpose of the present application can be achieved. For example, based on the mass of the first bonding coating layer, the mass percentage of the first polymer binder is 85% to 95%, the mass percentage of the thickener is 0.5% to 2%, the mass percentage of the auxiliary binder is 0% to 15%, and the mass percentage of the wetting agent is 4% to 10%.

[0062] In one embodiment of the present application, the coverage Cr2 of the second polymer binder in the second bonding coat per unit area is 40% to 60%. For example, the coverage of the second polymer binder in the second bonding coat per unit area is 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, and 60%, which is a range consisting of any two of these values. The coverage of the second polymer binder in the second bonding coat per unit area is regulated within the above range, and the second polymer binder provides a larger gap between the second bonding coat and the positive electrode sheet or between the second bonding coat and the negative electrode sheet. The secondary battery can have a wider electrolyte transmission channel during the cycle, and can fully realize the electrolyte flow channel between the electrode sheet and the separator. When the electrolyte has good flow wettability in the electrode sheet and the separator, the second bonding coat has a suitable thickness, thereby reducing the risk of energy density loss caused by the increase in volume of the fast-charging secondary battery due to the excessive thickness. In this way, the secondary battery can improve its energy density while taking into account both cycle performance and high temperature stability.

[0063] In one embodiment of the present application, the polymerizable monomers of the second polymer binder include at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, allyl chloride, acrylic acid, methyl acrylate, butyl acrylate, chlorostyrene, fluorostyrene, ethyl acrylate, ethyl methacrylate, methyl methacrylate, butyl methacrylate, ethyl chloromethylacrylate, styrene, butadiene, or acrylonitrile. The use of the aforementioned second polymer binders allows for a large gap between the second bonding coating and the positive electrode sheet, or between the second bonding coating and the negative electrode sheet, facilitating electrolyte transport and providing better heat dissipation during cycling, thereby improving the high-temperature storage performance and high-temperature stability of the secondary battery, and enabling the secondary battery to exhibit good cycling performance and high-temperature stability under fast-charging conditions.

[0064] In one embodiment of the present application, the second polymer binder includes a core-shell structure second polymer binder, the polymer monomer of the shell of the core-shell structure second polymer binder includes at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, styrene, butadiene, acrylonitrile, acrylic acid, methyl acrylate or butyl acrylate; the core of the core-shell structure second polymer binder includes at least one of ethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate or ethyl chloromethylacrylate. The selection of the above-mentioned type of second polymer binder can provide a large gap between the second bonding coating and the positive electrode sheet or between the second bonding coating and the negative electrode sheet, which is beneficial to the transmission of the electrolyte and better heat dissipation during the cycle, thereby improving the high-temperature storage performance of the secondary battery and improving the high-temperature stability of the secondary battery, so that the secondary battery has good cycle performance and high-temperature stability under fast charging conditions.

[0065] In one embodiment of the present application, the second polymer binder includes a non-core-shell structure second polymer binder, and the polymerized monomer of the non-core-shell structure second polymer binder includes at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, propylene, chlorostyrene, fluorostyrene, vinylidene chloride, vinylidene fluoride, hexafluoropropylene, vinyl chloride, or allyl chloride. The selection of the above-mentioned second polymer binder can provide a large gap between the second bonding coating and the positive electrode plate or between the second bonding coating and the negative electrode plate, which is beneficial for the transmission of the electrolyte and better heat dissipation during the cycle, thereby improving the high-temperature storage performance of the secondary battery and the high-temperature stability of the secondary battery, so that the secondary battery has good cycle performance and high-temperature stability under fast charging conditions.

[0066] In one embodiment of the present application, the second bonding coating layer includes a second polymer binder and an auxiliary binder. The auxiliary binder is applied to the second bonding coating layer, and the second polymer binder can be bonded to the isolation film substrate and the ceramic coating during the application of the second bonding coating slurry. The present application has no particular restrictions on the content of the second polymer binder and the auxiliary binder in the second bonding coating layer, as long as the purpose of the present application can be achieved. For example, based on the mass of the second bonding coating layer, the mass percentage of the second polymer binder is 85% to 95%, and the mass percentage of the auxiliary binder is 0% to 15%.

[0067] The present application does not particularly limit the types of thickeners, auxiliary binders, and wetting agents, as long as the purpose of the present application can be achieved. For example, thickeners include but are not limited to sodium carboxymethyl cellulose. For example, auxiliary binders include but are not limited to homopolymers or copolymers polymerized from at least one of the following monomers: ethyl acrylate, butyl acrylate, ethyl methacrylate, acrylic acid, methacrylic acid, maleic anhydride, dicarboxylic anhydride, acrylonitrile, butadiene, and monovinyl compounds. The present application does not particularly limit the types of the above-mentioned monovinyl compounds, as long as the purpose of the present application can be achieved. For example, monovinyl compounds include but are not limited to at least one of styrene, chlorostyrene, fluorostyrene, or methylstyrene. For example, wetting agents include but are not limited to sodium carboxymethyl cellulose, dimethyl siloxane, polyethylene oxide dimethyl siloxane, polyethylene oxide, oxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, oxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, polyoxyethylene polyoxypropylene block copolymer, or at least one of dioctyl sodium sulfosuccinate.

[0068] In one embodiment of the present application, the isolation membrane further comprises a ceramic coating, which is disposed between the isolation membrane substrate and the first bonding coating, and / or, the ceramic coating is disposed between the isolation membrane substrate and the second bonding coating. In some embodiments, as shown in FIG3 , the isolation membrane 30 comprises an isolation membrane substrate 31, a first bonding coating 32, a second bonding coating 33 and a ceramic coating 34, the first bonding coating 32 and the second bonding coating 33 are respectively disposed on both sides of the isolation membrane substrate 31, the ceramic coating 34 is disposed between the isolation membrane substrate 31 and the first bonding coating 32, and the second bonding coating 33 is adjacent to the surface of the isolation membrane substrate 31 away from the ceramic coating 34. In other embodiments, as shown in FIG4 , the isolation membrane 30 comprises an isolation membrane substrate 31, a first bonding coating 32, a second bonding coating 33 and a ceramic coating 34, the first bonding coating 32 and the second bonding coating 33 are respectively disposed on both sides of the isolation membrane substrate 31, the ceramic coating 34 is disposed between the isolation membrane substrate 31 and the second bonding coating 33, and the first bonding coating 32 is adjacent to the surface of the isolation membrane substrate 31 away from the ceramic coating 34. In some further embodiments, as shown in FIG5 , the separator 30 includes a separator substrate 31, a first bonding coating 32, a second bonding coating 33, and two ceramic coatings 34. The first bonding coating 32 and the second bonding coating 33 are respectively disposed on both sides of the separator substrate 31. One layer of ceramic coating 34 is disposed between the separator substrate 31 and the first bonding coating 32. Meanwhile, another layer of ceramic coating 34 is disposed between the separator substrate 31 and the second bonding coating 33. It should be noted that the two ceramic coating layers may be the same or different. The ceramic coating has good hardness and heat resistance. When the ceramic coating is disposed in the separator, it can prevent the separator from shrinking at high temperatures, thereby improving the hardness and heat resistance of the secondary battery. This allows the secondary battery to have good thermal safety performance and mechanical reliability on the basis of good dynamic performance and high-temperature stability. In the present application, it is preferred that the second bonding coating 33 faces the positive electrode plate, and the ceramic coating 34 is arranged between the isolation membrane substrate 21 and the second bonding coating 33 to store electrolyte. It can also provide additional electrolyte flow channels outside the electrolyte channels formed by the second bonding coating 33, which can reduce the thickness of the second bonding coating 33 and increase the energy density. At the same time, it can protect the isolation membrane substrate 31 from being oxidized by the high voltage of the positive electrode, and can also reduce the coating thickness of the second bonding coating 33.

[0069] In one embodiment of the present application, the ceramic coating includes ceramic particles and a ceramic coating binder. The present application does not particularly limit the types of ceramic particles and ceramic coating binders, as long as the purpose of the present application can be achieved. For example, ceramic particles include but are not limited to at least one of aluminum oxide, boehmite, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium hydroxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, or silicon nitride. The ceramic coating binder includes but is not limited to at least one of polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, polybutyl acrylate, or polyacrylonitrile. The present application does not particularly limit the content of ceramic particles and ceramic coating binder in the ceramic coating, as long as the purpose of the present application can be achieved. For example, based on the mass of the ceramic coating, the mass percentage of ceramic particles is 5% to 95%, and the mass percentage of ceramic coating binder is 5% to 95%. The present application does not particularly limit the average particle size of the ceramic particles, as long as the purpose of the present application can be achieved. For example, the average particle size of the ceramic particles is 1 μm to 3 μm. The present application does not particularly limit the thickness of the ceramic coating. For example, the thickness of the ceramic coating can be 0.5 μm to 6 μm. The present application does not particularly limit the isolation membrane substrate, as long as the purpose of the present application can be achieved. For example, the structure of the isolation membrane substrate includes a single-layer structure or a multi-layer composite structure, wherein the multi-layer composite structure can be a double-layer composite structure, a three-layer composite structure or a four-layer composite structure. The type of isolation membrane substrate includes at least one of polyethylene (PE), polypropylene (PP) or polyethylene terephthalate (PET). The thickness of the isolation membrane substrate can be 3 μm to 20 μm.

[0070] The present application does not particularly limit the method for controlling the average particle size of the ceramic particles, as long as the purpose of the present application can be achieved. For example, this can be achieved by directly purchasing ceramic particles with an average particle size within the range of the present application, or by crushing, grinding, or ball milling.

[0071] In one embodiment of the present application, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate. The chemical formula of the above-mentioned "lithium-rich manganese-based material" is LiMnO·LiMO, where M may include Ni n 、Co n or Mn n At least one of n can be 1, 2, or 3. The aforementioned positive electrode active materials have high surface activity and, when used in secondary batteries, can increase active sites for lithium ion insertion and extraction, reduce the electrochemical polarization of the secondary battery, and thus reduce the impedance of the secondary battery, thereby enabling the secondary battery to have good cycle performance while maintaining high-temperature stability.

[0072] In one embodiment of the present application, the positive electrode active material further includes a non-metallic element, and the non-metallic element includes at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. The present application has no particular restriction on the content of the non-metallic element in the positive electrode active material, as long as the purpose of the present application can be achieved. For example, based on the mass of the positive electrode active material, the mass percentage of the non-metallic element is 0.1% to 10%. For example, the mass percentage of the non-metallic element is 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two of these values. Including the above-mentioned types of non-metallic elements in the positive electrode active material can further improve the stability of the positive electrode active material, improve the structural stability of the positive electrode sheet, and thus improve the cycle performance of the secondary battery.

[0073] In one embodiment of the present application, the negative electrode active material includes at least one of a carbon-based material, a silicon-based material, or a tin-based material. The carbon-based material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, or mesocarbon microbeads. The silicon-based material includes at least one of a silicon material, a silicon-carbon material, or a silicon-oxygen material. The tin-based material includes at least one of elemental tin, a tin alloy, or a tin oxide. The above-mentioned negative electrode active materials have good surface activity and, when applied to secondary batteries, can increase active sites for lithium ion insertion and extraction, reduce the electrochemical polarization of the secondary battery, and thus reduce the impedance of the secondary battery, thereby enabling the secondary battery to have good cycle performance while maintaining high-temperature stability.

[0074] In one embodiment of the present application, the carbon-based material is tested by Raman with a peak intensity ratio of d peak to g peak of I d / I g Satisfy: 0.1≤I d / I g ≤1. For example, I d / I g is 0.1, 0.2, 0.4, 0.6, 0.8, 1 or a range consisting of any two of these values. This indicates that the carbon-based material surface contains amorphous carbon. The presence of amorphous carbon on the carbon-based material surface can enhance the electrochemical activity of the carbon-based material, making the lithium ion embedding smoother during the secondary battery cycle, thereby reducing the electrochemical polarization of the secondary battery, thereby reducing the internal impedance of the secondary battery and improving its cycle kinetics. The above I will be satisfied. d / I g The application of high-value carbon-based materials in secondary batteries is beneficial to further improve the cycle performance of secondary batteries on the basis of good high-temperature stability.

[0075] In this application, the d peak is the shift range of 1300 cm in the Raman spectrum of carbon-based material particles. -1 to 1400cm -1The peak of g is the shift range of 1530cm in the Raman spectrum of carbon-based material particles. -1 to 1630cm -1 Peak.

[0076] This application is for d / I g There is no particular limitation on the method for controlling the value of , as long as the purpose of this application can be achieved. For example, commercially available carbon-based materials with different amounts of amorphous carbon coated on their surfaces can be selected, and the I value of the carbon-based materials can be determined by combining the Raman test method in this application. d / I g , select the desired d / I g of carbon-based materials.

[0077] The present application does not impose any particular restrictions on the preparation method of the carbon-based material, as long as the purpose of the present application can be achieved. For example, the preparation method of the carbon-based material may include but is not limited to: after uniformly mixing the carbon-based material and amorphous carbon, heating to 500°C to 1500°C and then keeping warm for 10 hours to 20 hours to obtain a carbon-based material with amorphous carbon coated on the surface. The positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. In some embodiments, the positive electrode active material layer is disposed on one surface of the positive electrode current collector. In other embodiments, the positive electrode active material layer is disposed on both surfaces of the positive electrode current collector, wherein the above-mentioned "surface" can be part of the surface or the entire surface of the positive electrode current collector. The present application does not impose any particular restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). In the present application, there is no particular restriction on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm, preferably 6μm to 18μm. The thickness of the single-sided positive electrode material layer is 30μm to 120μm. In the present application, the positive electrode active material layer may further include a conductive agent and a binder. The present application does not particularly limit the type of positive electrode binder in the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application does not particularly limit the type of conductive agent in the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powders and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions on the mass ratio of the positive electrode active material, conductive agent and positive electrode binder in the positive electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0078] The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. In some embodiments, the negative electrode active material layer is disposed on one surface of the negative electrode current collector. In other embodiments, the negative electrode active material layer is disposed on both surfaces of the negative electrode current collector. The aforementioned "surface" can be part of the surface or the entire surface of the negative electrode current collector. The present application does not particularly limit the negative electrode current collector, as long as the objectives of the present application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.). In the present application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the objectives of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4μm to 20μm, and the thickness of the negative electrode active material layer is 30μm to 130μm. Optionally, the negative electrode active material layer may also include a conductive agent and a binder. The present application does not particularly limit the type of conductive agent in the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent can be the same type as the conductive agent in the above-mentioned positive electrode active material layer. The present application does not particularly limit the type of negative electrode binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the negative electrode binder can be the same type as the positive electrode binder in the above-mentioned positive electrode active material layer. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent and the negative electrode binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved.

[0079] The electrolyte in the secondary battery of the present application includes a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium bis(oxalatoborate), or lithium difluorooxalatoborate. The present application does not limit the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application does not particularly limit the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound, or other organic solvents. The carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluorocarbon compound. The chain carbonate compound may include but is not limited to at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, or methylethyl carbonate. The cyclic carbonate may include but is not limited to at least one of ethylene carbonate, propylene carbonate (PC), butylene carbonate, or vinylethylene carbonate. The fluorinated carbonate compound may include, but is not limited to, at least one of fluorinated ethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The electrolyte in the secondary battery of the present application may also include additives. The present application does not particularly limit the type of additives, as long as the purpose of the present application can be achieved. For example, the additive includes but is not limited to at least one of succinonitrile, glutaronitrile, pimelonitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2-bis(2-cyanoethoxy)propane or 1,2(3-cyanopropoxy)ethane. The present application does not impose any limitation on the content of the additive in the electrolyte, as long as the purpose of the present application can be achieved.

[0080] In one embodiment of the present application, the secondary battery further comprises a housing, in which the electrode assembly and electrolyte are housed. The present application does not particularly limit the housing and may be any known housing in the art, as long as it can achieve the objectives of the present application. For example, the housing includes, but is not limited to, an aluminum-plastic film or a steel shell.

[0081] The present application does not particularly limit the type of secondary battery, which may include any device that undergoes an electrochemical reaction. For example, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), sodium ion secondary batteries (sodium ion batteries), lithium polymer secondary batteries, and lithium ion polymer secondary batteries.

[0082] The present application has no particular limitation on the method for preparing the isolation membrane, as long as the purpose of the present application can be achieved.

[0083] For example, in one embodiment, the preparation method of the isolation membrane includes but is not limited to the following steps: (1) uniformly mixing a first polymer binder, a thickener, an auxiliary binder and a wetting agent to obtain a first bonding coating slurry; (2) uniformly mixing a second polymer binder and an auxiliary binder to obtain a second bonding coating slurry; (3) coating the first bonding coating slurry on one surface of the isolation membrane substrate, and forming a first bonding coating on one surface of the isolation membrane substrate after drying; coating the second bonding coating slurry on the other surface of the isolation membrane substrate, and forming a second bonding coating on the other surface of the isolation membrane substrate after drying, thereby obtaining an isolation membrane.

[0084] For example, in another embodiment, the preparation method of the isolation membrane includes but is not limited to the following steps: (1) mixing a first polymer binder, a thickener, an auxiliary binder and a wetting agent evenly to obtain a first bonding coating slurry; (2) mixing a second polymer binder and an auxiliary binder evenly to obtain a second bonding coating slurry; (3) mixing ceramic particles and a ceramic coating binder evenly to obtain a ceramic coating slurry; (4) coating the ceramic coating slurry on one surface of the isolation membrane substrate, and after drying, forming a ceramic coating on one surface of the isolation membrane substrate; coating the first bonding coating slurry on the surface of the ceramic coating, and after drying, forming a first bonding coating on the surface of the ceramic coating away from the isolation membrane substrate; coating the second bonding coating slurry on the other surface of the isolation membrane substrate, and after drying, forming a second bonding coating on the other surface of the isolation membrane substrate, thereby preparing the isolation membrane.

[0085] For example, in another embodiment, the preparation method of the isolation membrane includes but is not limited to the following steps: (1) mixing a first polymer binder, a thickener, an auxiliary binder and a wetting agent evenly to obtain a first bonding coating slurry; (2) mixing a second polymer binder and an auxiliary binder evenly to obtain a second bonding coating slurry; (3) mixing ceramic particles and a ceramic coating binder evenly to obtain a ceramic coating slurry; (4) coating the ceramic coating slurry on one surface of the isolation membrane substrate, and after drying, forming a ceramic coating on one surface of the isolation membrane substrate; coating the second bonding coating slurry on the surface of the ceramic coating, and after drying, forming a second bonding coating on the surface of the ceramic coating away from the isolation membrane substrate; coating the first bonding coating slurry on the other surface of the isolation membrane substrate, and after drying, forming the first bonding coating on the other surface of the isolation membrane substrate, thereby obtaining an isolation membrane.

[0086] For example, in another embodiment, the preparation method of the isolation membrane includes but is not limited to the following steps: (1) mixing a first polymer binder, a thickener, an auxiliary binder and a wetting agent evenly to obtain a first bonding coating slurry; (2) mixing a second polymer binder and an auxiliary binder evenly to obtain a second bonding coating slurry; (3) mixing ceramic particles and a ceramic coating binder evenly to obtain a ceramic coating slurry; (4) coating the ceramic coating slurry on one surface of the isolation membrane substrate, and after drying, forming a ceramic coating on one surface of the isolation membrane substrate; coating the ceramic coating slurry on the other surface of the isolation membrane, and after drying, forming a ceramic coating on the other surface of the isolation membrane substrate; coating the second bonding coating slurry on the surface of the first ceramic coating away from the isolation membrane substrate, and after drying, forming a second bonding coating on the surface of the first ceramic coating away from the isolation membrane substrate; coating the first bonding coating slurry on the surface of the second ceramic coating away from the isolation membrane substrate, and after drying, forming a first bonding coating on the surface of the second ceramic coating away from the isolation membrane substrate, thereby obtaining an isolation membrane.

[0087] The present application has no particular restrictions on the solid content of the above-mentioned first bonding coating slurry, as long as the purpose of this application can be achieved. For example, the solid content of the first bonding coating slurry is 60wt% to 80wt%. The present application has no particular restrictions on the solid content of the above-mentioned second bonding coating slurry, as long as the purpose of this application can be achieved. For example, the solid content of the second bonding coating slurry is 60wt% to 80wt%. The present application has no particular restrictions on the solid content of the above-mentioned ceramic coating slurry, as long as the purpose of this application can be achieved. For example, the solid content of the ceramic coating slurry is 30wt% to 40wt%. The present application has no particular restrictions on the temperature and time of the above-mentioned drying, and those skilled in the art can select and adjust according to actual needs, as long as the purpose of this application can be achieved.

[0088] The present application does not impose any particular restrictions on the preparation method of the secondary battery, and any preparation method known in the art may be selected as long as the purpose of the present application can be achieved. For example, the preparation method of the secondary battery includes but is not limited to the following steps: stacking the separator, the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and winding, folding, and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the separator, the positive electrode sheet, the separator, and the negative electrode sheet in sequence, fixing the four corners of the entire stacked structure to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery.

[0089] The second aspect of the present application provides an electric device, which includes the secondary battery according to any one of the aforementioned embodiments. Therefore, the electric device has good performance.

[0090] The electrical device of the present application is not particularly limited and may be any electrical device known in the art. For example, the electrical device may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0091] Example

[0092] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods.

[0093] Test methods and equipment:

[0094] Relevant particle size tests:

[0095] The average particle size of the first polymer binder and the second polymer binder can be observed by scanning electron microscopy (SEM) on the corresponding surface of the isolation membrane perpendicular to the thickness direction, and the diameters of 10 first polymer binder and 10 second polymer binder particles are measured to find the average value. Wherein, the first polymer binder and the second polymer binder are distinguished by the size of the particle diameter. Specifically, on the surface of the isolation membrane, the side with a relatively smaller diameter of each particle is the first bonding coating containing the first polymer binder, and 10 first polymer binders are arbitrarily selected in the first bonding coating to obtain the average particle size of the first polymer binder; the side with a relatively larger diameter of each particle is the second bonding coating containing the second polymer binder, and 10 second polymer binders are arbitrarily selected in the second bonding coating to obtain the average particle size of the second polymer binder. Since the particles of the first polymer binder and the second polymer binder will be deformed under the pressure of cold pressing, hot pressing and other processes during the preparation of the secondary battery, the diameters of the particles along the thickness direction of the isolation membrane and the direction perpendicular to the thickness direction of the isolation membrane are different. The average particle size of the first polymer binder and the second polymer binder of the present application is the diameter measured on the surface of the particles perpendicular to the thickness direction of the isolation membrane. Therefore, the average particle size of the above-mentioned first polymer binder and the second polymer binder is not limited by the thickness of the first bonding coating and the second bonding coating.

[0096] The average particle size of the ceramic particles on the separator can be determined by observing the surface of the separator perpendicular to its thickness using a scanning electron microscope (SEM). The diameters of ten ceramic particles are measured and the average is calculated. The average diameter of the ceramic particles in this application is the diameter measured perpendicular to the thickness of the separator. Therefore, the average particle size of the ceramic particles is not limited by the thickness of the ceramic coating.

[0097] The Dv50 and Dv99 of the positive and negative active materials were measured using a laser particle size analyzer.

[0098] (1) Coating weight W of the positive electrode active material layer z test:

[0099] The lithium-ion battery was discharged at 0.5C to 3.0V and then disassembled to obtain the positive electrode. The impurities on the surface of the positive electrode were cleaned with dimethyl carbonate (DMC) and dried. The area of ​​the cut piece was A mm 2 The positive electrode sheet sample is placed on a balance and weighed, which is recorded as p1. The positive electrode active material layer on the positive electrode sheet is then washed clean, and the positive electrode current collector is placed on a balance and weighed, which is recorded as p2.

[0100] If the positive electrode sheet is coated with a positive electrode active material layer on one side, W z =(p1-p2) / A.

[0101] If it is a positive electrode sheet coated with a positive electrode active material layer on both sides, W z =(p1-p2) / 2A.

[0102] (2) Coating weight W of negative electrode active material layer f test:

[0103] The lithium-ion battery was discharged at 0.5C to 3.0V and then disassembled to obtain the negative electrode. The impurities on the surface of the negative electrode were cleaned with DMC and dried. The area B mm was cut. 2 The negative electrode sheet sample is placed on a balance and weighed, which is recorded as q1. Then the negative electrode active material layer on the negative electrode sheet is washed clean, and the negative electrode current collector is placed on a balance and weighed, which is recorded as q2.

[0104] If the negative electrode sheet is coated with a negative electrode active material layer on one side, W f =(q1-q2) / B.

[0105] If it is a negative electrode sheet with negative electrode active material layer coated on both sides, W f =(q1-q2) / 2B.

[0106] Test of single-sided coating weight of the first bonding coat:

[0107] The lithium-ion batteries of the examples and comparative examples were discharged at 0.5C to 3.0V, and then disassembled to obtain the separators. The impurities on the separator surface were cleaned with DMC and dried at 60°C to obtain the test samples of the separators. An area of ​​S mm was punched out on the test samples of the separators. 2 The small disc is weighed and recorded as m1, and then the first bonding coating on the small disc is peeled off to obtain the mass of the small disc after peeling off the first bonding coating, which is recorded as m2. The single-sided coating weight of the first bonding coating = (m1-m2) / S.

[0108] Test for single-sided coating weight of the second bonding coat:

[0109] The lithium-ion batteries of the examples and comparative examples were discharged at 0.5C to 3.0V, and then disassembled to obtain the separators. The impurities on the separator surface were cleaned with DMC and dried at 60°C to obtain the test samples of the separators. An area of ​​S mm was punched out on the test samples of the separators. 2 The small disc is weighed and recorded as m3, and then the second adhesive coating on the small disc is peeled off to obtain the mass of the small disc after peeling off the second adhesive coating, which is recorded as m4. The single-sided coating weight of the first adhesive coating = (m3-m4) / S

[0110] Tests for first and second bond coat thickness:

[0111] The coated separator was subjected to argon ion polishing to obtain a cross-section of the separator. The cross-section was observed using a scanning electron microscope (SEM) to measure the thickness of the first and second bonding coating layers. In the separator cross-section, the side with the smaller particle diameter represents the first bonding coating layer containing the first polymer binder, while the side with the larger particle diameter represents the second bonding coating layer containing the second polymer binder.

[0112] Test of coverage of the first polymer binder:

[0113] The surface of the isolation membrane provided with the first adhesive coating was observed by SEM, and the coverage was obtained by dividing the area occupied by the first polymer binder in the electron microscope photograph by the area of ​​the isolation membrane sampled in the entire electron microscope photograph.

[0114] Second polymer binder coverage test:

[0115] The surface of the isolation membrane provided with the second adhesive coating was observed by SEM, and the coverage was obtained by dividing the area occupied by the second polymer adhesive in the electron microscope photograph by the area of ​​the isolation membrane sampled in the entire electron microscope photograph.

[0116] Raman test:

[0117] The lithium-ion battery was discharged at 0.5C to 3.0V and then disassembled to obtain the negative electrode sheet. After cleaning with dimethyl carbonate and drying, an area of ​​100 μm × 100 μm was selected on the negative electrode active material layer. A laser microconfocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instrument Division) was used to scan the negative electrode active material particles within the area to obtain the d peak and g peak of all the negative electrode active material particles within the area. The data was processed using LabSpec software to obtain the peak intensities of the d peak and g peak of each negative electrode active material particle, which were I d and I g The laser wavelength of the Raman spectrometer is in the range of 532nm to 785nm. d / I g The value of I of all negative electrode active material particles measured within this range d and I g The average of the ratios.

[0118] Test of the bonding force F1 of the separator to the positive electrode:

[0119] The dry-pressed adhesion strength between the separator and the positive electrode sheet was measured using the 180° peel test standard. The lithium-ion batteries in the tested examples and comparative examples were disassembled, the negative electrode sheet was peeled off, and the separator and positive electrode sheet were soaked in dimethyl carbonate for 20 minutes to remove the electrolyte. The separator and positive electrode sheet were then cut into 54.2 mm × 72.5 mm samples. The separator and positive electrode sheet were then laminated and hot-pressed using a hot press at 85°C, 1 MPa, and 85 seconds. The laminated sample was then cut into 15 mm × 54.2 mm strips to obtain test strips for the separator-to-positive electrode sheet adhesion test. A 15 mm × 55 mm piece of double-sided tape (NITTO.NO5000NS) was applied to a steel plate, and the test strip was then attached to the double-sided tape with the test surface facing down. Connect a 15mm×70mm paper tape to one end of the test specimen with double-sided tape, and manually push a small stick with a mass of 2kg to roll on the test specimen 8 times to obtain a test sample. Use a tensile testing machine for testing. Fix the test sample on the test bench, fold the paper tape 180° upwards, and fix it with a clamp. Then the tensile testing machine starts pulling the paper tape at a speed of 50mm / min until the isolation film on the surface of the double-sided tape and the positive electrode are separated. End the test and save the test data. The bonding force F1 between the isolation film and the positive electrode is calculated based on the tensile force and the stretched displacement when the isolation film and the positive electrode are separated. The unit is N / m.

[0120] Test of the bonding force F2 of the separator to the negative electrode:

[0121] The dry-pressed adhesion strength between the separator and the negative electrode sheet was measured using the 180° peel test standard. The lithium-ion batteries in the tested examples and comparative examples were disassembled, the positive electrode sheet peeled off, and the separator and negative electrode sheet were soaked in dimethyl carbonate for 20 minutes to remove the electrolyte. The separator and negative electrode sheet were then cut into 54.2 mm × 72.5 mm samples. The separator and negative electrode sheet were then laminated and hot-pressed using a hot press at 85°C, 1 MPa, and 85 seconds. The laminated sample was then cut into 15 mm × 54.2 mm strips to obtain test specimens for the separator-to-negative-electrode adhesion test. The adhesion strength F2 between the separator and the negative electrode sheet was then measured using the same procedure as described for the separator-to-positive-electrode adhesion test (unit: N / m).

[0122] Cycle performance test:

[0123] The lithium-ion batteries in the embodiments and comparative examples were subjected to a cycle performance test at a charge rate of 10C, and the specific steps were as follows:

[0124] Adjust the test temperature to 25℃ and start the test: (1) 10C constant current charging to 4.2V; (2) 8C constant current charging to 4.3V; (3) 6C constant current charging to 4.45V; (4) 4.45V constant voltage charging to 0.05C; (5) stand for 5 minutes; (6) 1C constant current discharge to 3.0V; (7) stand for 5 minutes; (8) cycle steps (1) to (7) for 1000 times (cls); end;

[0125] Capacity retention (%) = discharge capacity after 1000 cycles / first cycle discharge capacity × 100%.

[0126] High temperature stability test:

[0127] Test the thickness of the lithium-ion battery after it is manufactured, referred to as the initial thickness of the lithium-ion battery;

[0128] The lithium-ion battery is fully charged according to the following steps: charge at a constant current of 0.7C to 4.45V, and charge at a constant voltage of 4.45V to 0.02C;

[0129] The lithium-ion battery was placed in a high and low temperature box at 80°C for 8 hours, and the thickness of the lithium-ion battery after storage was tested, and the test was completed.

[0130] The expansion rate of the lithium-ion battery = (thickness of the lithium-ion battery after high-temperature storage - initial thickness of the lithium-ion battery) / initial thickness of the lithium-ion battery × 100%. The expansion rate is used to characterize high-temperature stability. The smaller the expansion rate, the better the high-temperature stability.

[0131] Example 1-1

[0132] <Preparation of Separator>

[0133] A single-layer polypropylene film with a thickness of 5 μm is used as the base material of the isolation membrane;

[0134] The ceramic particles aluminum oxide, ceramic coating binder butadiene-styrene polymer (butadiene and styrene mass ratio 2:3, weight average molecular weight Mw = 7 × 10 6 ), solvent deionized water is mixed according to a mass ratio of 35:10:55. Specifically, 30 kg of butadiene-styrene polymer and deionized water are first added to a double planetary mixer with a volume of 60 L, and dispersed at 45° C. for 3 hours; then 16.1 kg of aluminum oxide ceramic particles are added to the mixer and dispersed at high speed at 45° C. for 2 hours; then, ball milling is performed using a nano grinder for 1.5 hours, using spherical zirconium oxide beads with a diameter of 6 μm as the grinding medium to obtain a ceramic coating slurry; the average particle size of the ceramic particles is 2 μm;

[0135] The first polymer binder polyacrylic acid (Mw = 4500), the thickener sodium carboxymethyl cellulose (Mw = 7.6 × 10 3 ) and a wetting agent polyoxyethylene ether (Mw = 6000) were mixed in a mass ratio of 91:0.5:8.5, deionized water was added as a solvent, and the mixture was stirred evenly to form a first bonding coating slurry with a solid content of 75 wt%; the average particle size of the first polymer binder was 1.6 μm; the first polymer binder had a non-core-shell structure;

[0136] The second polymer binder polyvinylidene fluoride (Mw = 8 × 10 5 ) and an auxiliary binder methacrylic acid are mixed in a mass ratio of 90:10, deionized water is added as a solvent, and the mixture is stirred evenly to form a second bonding coating slurry with a solid content of 76 wt %; the average particle size of the second polymer binder is 25 μm; the second polymer binder is a non-core-shell structure;

[0137] A ceramic coating slurry is coated on one surface of the isolation membrane substrate, and after drying at 60°C, a ceramic coating is formed on one surface of the isolation membrane substrate; a second bonding coating slurry is coated on the surface of the ceramic coating away from the isolation membrane substrate, and after drying at 60°C, a second bonding coating is formed on the surface of the ceramic coating away from the isolation membrane substrate; a first bonding coating slurry is coated on the other surface of the isolation membrane substrate, and after drying at 60°C, a first bonding coating is formed on the other surface of the isolation membrane substrate, thereby obtaining an isolation membrane (see Figure 4 for the structure, but not limited to Figure 4).

[0138] The single-sided coating weight of the first adhesive coating layer is Cw1 = 0.0006 mg / mm 2 The thickness of the first bonding coating layer is H1 = 2 μm, and the single-sided coating weight of the second bonding coating layer is Cw2 = 0.0012 mg / mm 2 The thickness of the second bonding coating is H2 = 12 μm. The single-sided coating weight of the ceramic coating is Cw3 = 10.0023 mg / mm 2 The thickness of the ceramic coating is H3 = 1 μm. The coverage rate Cr1 of the first polymer binder per unit area in the first bonding coating is 50%, and the coverage rate Cr2 of the second polymer binder per unit area in the second bonding coating is 50%.

[0139] <Preparation of positive electrode sheet>

[0140] The positive electrode active material is lithium cobalt oxide (LiCoO2, Dv99 = 30 μm, Dv50 = 12 μm), the positive electrode conductor is superconducting carbon (Super P), and the positive electrode binder is polyvinylidene fluoride (PVDF, Mw = 7 × 10 6) are mixed in a mass ratio of 97:1:2, N-methylpyrrolidone (NMP) is added as a solvent, and stirred under the action of a vacuum mixer until the solid content is 75wt% and the system is uniform. The positive electrode slurry is evenly coated on the positive electrode main area on one surface of the positive electrode current collector aluminum foil with a thickness of 10μm, and dried at 95°C to obtain a positive electrode sheet with a single-sided positive electrode active material layer. Thereafter, the above steps are repeated on the positive electrode main area on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode active material layer. It is then cold pressed, cut into pieces, and slit, and then dried at 85°C under vacuum conditions for 4h to obtain a positive electrode sheet with a specification of 54mm×1580mm for use. Among them, the single layer thickness of the positive electrode active material layer is 38.5μm, the thickness of the positive electrode sheet is 87μm, and the tab area of ​​the positive electrode collector is formed into 18 positive tabs by die-cutting. The coating weight of the positive electrode active material layer is W z 9.08 mg / cm 2 .

[0141] <Preparation of negative electrode sheet>

[0142] The negative electrode active material (Dv99 = 25 μm, Dv50 = 10 μm), negative electrode conductive agent Super P, stabilizer sodium carboxymethyl cellulose (CMC-Na, Mw = 7 × 10 5 ), negative electrode binder styrene-butadiene rubber (SBR, Mw = 5 × 10 6 ) were mixed in a mass ratio of 96.5:1.0:1.0:1.5, and then deionized water was added as a solvent. The mixture was stirred in a vacuum mixer until a solid content of 51 wt% and a uniform system was obtained. The negative electrode slurry was evenly coated on the negative electrode main area of ​​one surface of a 6 μm thick negative electrode current collector copper foil and dried at 85°C to obtain a negative electrode sheet coated with a negative electrode active material layer on one side. The above steps were then repeated on the negative electrode main area of ​​the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. The sheet was then cold pressed, cut into pieces, and slit. After slitting, it was dried at 110°C under vacuum for 4 hours to obtain a negative electrode sheet with a specification of 58 mm × 1600 mm for use. The thickness of the negative electrode active material layer is 58.5 μm, the thickness of the negative electrode sheet is 123 μm, and the tab area of ​​the negative electrode current collector is formed into 18 negative tabs by die-cutting. The coating weight of the negative electrode active material layer is W f 4.54 mg / cm 2 The types of negative electrode active materials are shown in Table 3.

[0143] <Preparation of Electrolyte>

[0144] In an environment with a water content of less than 10 ppm, n-propyl propionate, ethylene carbonate, and diethyl carbonate are mixed in a mass ratio of 40:30:30 as a solvent, and the lithium salt lithium fluorophosphate (LiPF6), solvent, and additive succinonitrile are prepared in a mass ratio of 15:83:2 to obtain an electrolyte, wherein the mass percentage of the lithium salt is 15%.

[0145] <Preparation of lithium-ion batteries>

[0146] The separator, positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The first adhesive coating layer in the separator is adjacent to the negative electrode sheet, while the second adhesive coating layer is adjacent to the positive electrode sheet. The electrode assembly is then wound together. The electrode assembly is placed in an aluminum-plastic film casing, dried, and then injected with electrolyte. The lithium-ion battery is then produced through vacuum packaging, resting, formation, capacity measurement, degassing, and trimming.

[0147] Example 1-2 to Example 1-21

[0148] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0149] Example 2-1 to Example 2-12

[0150] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1.

[0151] Example 3-1

[0152] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as Example 1-1.

[0153] Example 3-2 to Example 3-4

[0154] The process was the same as Example 1-1, except that artificial graphite coated with amorphous carbon was used as the negative electrode active material in the preparation of the negative electrode sheet. The mass ratio of artificial graphite to amorphous carbon was adjusted according to Table 3.

[0155] Example 3-5 and Example 3-6

[0156] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as Example 1-1.

[0157] Comparative Examples 1 to 12

[0158] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0159] Comparative Example 13

[0160] <Preparation of Separator>

[0161] A ceramic coating slurry is coated on one surface of an isolation membrane substrate, and after drying at 60°C, a ceramic coating is formed on one surface of the isolation membrane substrate; a first bonding coating slurry is coated on the surface of the ceramic coating away from the isolation membrane substrate, and after drying at 60°C, a first bonding coating is formed on the surface of the ceramic coating away from the isolation membrane substrate; the first bonding coating slurry is coated on the other surface of the isolation membrane substrate, and after drying at 60°C, a first bonding coating is formed on the other surface of the isolation membrane substrate, thereby producing an isolation membrane.

[0162] The rest is the same as Example 1-1.

[0163] <Preparation of lithium-ion batteries>

[0164] Except that the surface of the separator provided with the ceramic coating is closer to the positive electrode sheet, the rest is the same as Example 1-1.

[0165] <Preparation of positive electrode sheet>, <Preparation of negative electrode sheet>, and <Preparation of electrolyte> are the same as those in Comparative Example 1.

[0166] Comparative Example 14

[0167] <Preparation of Separator>

[0168] A ceramic coating slurry is coated on one surface of an isolation membrane substrate, and after drying at 60°C, a ceramic coating is formed on one surface of the isolation membrane substrate; a second bonding coating slurry is coated on the surface of the ceramic coating away from the isolation membrane substrate, and after drying at 60°C, a second bonding coating is formed on the surface of the ceramic coating away from the isolation membrane substrate; a second bonding coating slurry is coated on the other surface of the isolation membrane substrate, and after drying at 60°C, a second bonding coating is formed on the other surface of the isolation membrane substrate, thereby producing an isolation membrane.

[0169] The rest is the same as Example 1-1.

[0170] <Preparation of positive electrode sheet>, <Preparation of negative electrode sheet>, <Preparation of electrolyte>, and <Preparation of lithium-ion battery> are the same as those in Comparative Example 13.

[0171] Comparative Example 15

[0172] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0173] Comparative Example 16

[0174] <Preparation of Isolation Film> and <Preparation of Lithium-ion Battery> are the same as those in Comparative Example 14, and except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as those in Example 1-1.

[0175] Comparative Example 17

[0176] <Preparation of Isolation Film> and <Preparation of Lithium-ion Battery> are the same as those in Comparative Example 13, and except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as those in Example 1-1.

[0177] Comparative Example 18

[0178] <Preparation of Isolation Film> and <Preparation of Lithium-ion Battery> are the same as those in Comparative Example 14, and except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as those in Example 1-1.

[0179] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0180] Table 1

[0181] Note: “ / ” in Table 1 indicates no corresponding parameter; the difference between Example 1-1 and Example 1-21 in Table 1 is:

[0182] In the lithium-ion battery of Example 1-1, the first bonding coating in the isolation membrane is close to the negative electrode plate, and the second bonding coating is close to the positive electrode plate. In the lithium-ion battery of Example 1-21, the first bonding coating in the isolation membrane is close to the positive electrode plate, and the second bonding coating is close to the negative electrode plate.

[0183] It can be seen from Examples 1-1 to 1-21 and Comparative Examples 1 to 18 that the secondary battery of the embodiment of the present application is provided with a first bonding coating and a second bonding coating on both sides of the separator, and the Dv50 of the first polymer binder in the first bonding coating and the Dv50 of the second polymer binder in the second bonding coating are within the scope of the present application, and the Dv99 of the positive electrode active material and the Dv99 of the negative electrode active material are within the scope of the present application, and the coating weight W of the negative electrode active material layer is f and the coating weight W of the positive electrode active material layer z Within the scope of this application, the separator's bonding force F1 to the positive electrode sheet and the separator's bonding force F2 to the negative electrode sheet are increased, and the secondary battery has a higher capacity retention rate at a charge rate of 10C, indicating that the secondary battery has better cycle performance under fast charging conditions. The secondary battery has a lower thickness expansion rate after storage at 80°C for 8 hours, indicating that the secondary battery has better high-temperature stability. Therefore, the secondary battery of the embodiment of this application can simultaneously have good cycle performance and high-temperature stability under fast charging conditions.

[0184] The coating weight of the positive electrode active material and the coating weight of the negative electrode active material in Comparative Example 1 are both too low. Although the lithium ion battery obtained therefrom has good cycle performance and low expansion rate, the coating weight of the positive electrode active material layer and the negative electrode active material layer is too low. The cost of accurately controlling the coating weight in actual industrial production is too high. The qualified rate of the lithium ion battery obtained in large-scale production is too low and the energy density of the lithium ion battery obtained is too low, which cannot meet the needs of actual production and is not suitable for industrial production application. The secondary batteries of Comparative Examples 2 to 5 have a coating weight of the negative electrode active material layer of W f and / or the coating weight W of the positive electrode active material layer z is not within the scope of the present application; the Dv99 of the positive electrode active material and / or the negative electrode active material of the secondary batteries of Comparative Examples 6 to 8 is not within the scope of the present application; the Dv50 of the first polymer binder in the isolation membrane of the secondary batteries of Comparative Examples 9 and 10 is not within the scope of the present application; the Dv50 of the second polymer binder in the isolation membrane of the secondary batteries of Comparative Examples 11 and 12 is not within the scope of the present application; the second battery of Comparative Example 13 has a first bonding coating on both sides of its isolation membrane, rather than the isolation membrane structure of the present application; the second battery of Comparative Example 14 has a second bonding coating on both sides of its isolation membrane, rather than the isolation membrane structure of the present application; the second battery of Comparative Example 15 has a Dv99 of the positive electrode active material not within the scope of the present application; the second battery of Comparative Example 16 has a Dv99 of the negative electrode active material not within the scope of the present application; the second battery of Comparative Example 17 has a coating weight W of the positive electrode active material layer z It is not within the scope of this application, and both sides of the separator are provided with a first bonding coating, rather than the separator structure of this application; the secondary battery of Comparative Example 18, the Dv99 of the positive electrode active material, the Dv99 of the negative electrode active material, the coating weight W of the negative electrode active material layer f and the coating weight W of the positive electrode active material layer z and the isolation membrane are not within the scope of the present application; in the secondary batteries of Comparative Examples 1 to 18, the adhesion F1 of the isolation membrane to the positive electrode sheet and / or the adhesion F2 of the isolation membrane to the negative electrode sheet are lower, and the secondary battery has a lower capacity retention rate at a charging rate of 10C, indicating that the secondary battery has worse cycle performance under fast charging conditions, or the thickness of the secondary battery has a higher expansion rate after being stored at 80°C for 8h, indicating that the secondary battery has worse high-temperature stability, that is, Comparative Examples 2 to Comparative Examples 18 cannot take into account both high cycle performance and low expansion rate.

[0185] The coating weight W of the positive electrode active material layer z It usually affects the cycle performance and high temperature stability of the secondary battery. From Examples 1-4 to 1-7, it can be seen that the selection of W zThe secondary battery within the scope of this application has a high capacity retention rate at a charge rate of 10C, indicating that the secondary battery has good cycle performance under fast charging conditions and a low thickness expansion rate after storage at 80°C for 8 hours, indicating that the secondary battery has good high-temperature stability. The coating weight W of the positive electrode active material layer in Examples 1-6 is z The coating weight of the negative electrode active material layer is relatively low, and the coating weight of the positive electrode active material layer is relatively small. When the potential of the secondary battery is reached, the delithiation rate of the positive electrode increases, which may lead to the occurrence of excessive delithiation of the positive electrode, thereby reducing the capacity retention rate of the lithium-ion battery. Furthermore, although the charging speed of the lithium-ion battery is relatively fast and the impedance is relatively low, the energy density of the lithium-ion battery is relatively low. In actual industrial production, it is difficult to control the coating weight of the positive electrode active material layer. In Examples 1-7, the coating weight W of the positive electrode active material layer is relatively high. z The coating weight of the negative electrode active material layer is relatively high, and the coating weight of the positive electrode active material layer is quite different from that of the positive electrode active material layer. When the lithium-ion battery is fast charged, the lithium ions in the positive electrode sheet cannot be released in time, and the lithium ions cannot be embedded in the negative electrode sheet in time, which can easily lead to the occurrence of lithium plating, thereby reducing the capacity retention rate of the lithium-ion battery.

[0186] The Dv50 of the positive electrode active material and the Dv50 of the negative electrode active material generally affect the cycling performance and high-temperature stability of a secondary battery. As can be seen from Examples 1-1, 1-8, and 1-16, secondary batteries using positive and negative electrode active materials with Dv50 values ​​within the ranges of this application exhibit both high capacity retention at a 10C charge rate and low thickness expansion after storage at 80°C for 8 hours, demonstrating that the secondary batteries exhibit both good cycling performance and high-temperature stability under fast-charging conditions.

[0187] The positional relationship between the first and second adhesive coatings in the separator and the positive and negative electrode sheets typically affects the kinetic performance, cycling performance, and mechanical reliability of a secondary battery. As can be seen from Examples 1-1 and 1-21, the poor adhesion between the second polymer binder, polyvinylidene fluoride, and the negative electrode sheet results in a low adhesion force F2 between the separator and the negative electrode sheet, resulting in a larger expansion rate in Example 1-21 relative to that of Example 1-1. Furthermore, because the second adhesive coating in Example 1-21 corresponds to the negative electrode sheet, the lithium ion transmission path is longer during fast charging, resulting in lower kinetic performance, namely, capacity retention, in Example 1-21.

[0188] Table 2

[0189] The coverage rate Cr1 of the first polymer binder in the first bonding coat per unit area, the single-sided coating weight Cw1 of the first bonding coat, and the thickness H1 of the first bonding coat generally affect the cycle dynamics and high-temperature stability of the secondary battery. As can be seen from Examples 1-1, 2-1, and 2-4, the secondary battery selected for which the coverage rate Cr1 of the first polymer binder in the first bonding coat per unit area, the single-sided coating weight Cw1 of the first bonding coat, and the thickness H1 of the first bonding coat are within the scope of this application has a separator with a strong adhesion to the positive or negative electrode sheet, a high capacity retention rate at a charge rate of 10C, and a low thickness expansion rate after storage at 80°C for 8 hours, indicating that the secondary battery has both good cycle performance and good high-temperature stability under fast charging conditions.

[0190] The coverage rate Cr2 of the second polymer binder per unit area of ​​the second bonding coat, the single-sided coating weight Cw2 of the second bonding coat, and the thickness H2 of the second bonding coat generally affect the cycling performance and high-temperature stability of the secondary battery. As can be seen from Examples 1-1, 2-5, and 2-8, for secondary batteries selected with the coverage rate Cr2 of the second polymer binder per unit area of ​​the second bonding coat, the single-sided coating weight Cw2 of the second bonding coat, and the thickness H2 of the second bonding coat within the scope of this application, the separator has a strong adhesion to the positive or negative electrode sheet and a high capacity retention rate at a charge rate of 10C, indicating that the secondary battery has good cycling performance under fast charging conditions. The thickness has a low expansion rate after storage at 80°C for 8 hours, indicating that the secondary battery has good high-temperature stability.

[0191] The type of first polymer binder generally affects the cycling performance and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 2-9, and 2-10, secondary batteries using a first polymer binder within the scope of this application have separators with strong adhesion to the positive or negative electrode sheets and high capacity retention at a 10C charge rate, indicating good cycling performance under fast-charging conditions. They also have a low thickness expansion rate after storage at 80°C for 8 hours, indicating good high-temperature stability.

[0192] The type of second polymer binder typically affects the cycling performance and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 2-11, and 2-12, secondary batteries using a second polymer binder within the scope of this application exhibit strong adhesion between their separators and the positive or negative electrode sheets, high capacity retention at a 10C charge rate, and good cycling performance under fast-charging conditions. Furthermore, their thickness exhibits a low expansion rate after storage at 80°C for 8 hours, demonstrating good high-temperature stability.

[0193] Table 3 Note: “ / ” in Table 3 indicates no corresponding parameter.

[0194] Types of negative electrode active materials, carbon-based materials d / I g The value usually affects the cycle performance and high temperature stability of the secondary battery. From Example 1-1, Example 3-1 to Example 3-4, it can be seen that the type of negative electrode active material, the I of the carbon-based material d / I g The secondary battery with a value within the range of this application has a high capacity retention rate at a charging rate of 10C, indicating that the secondary battery has good cycle performance under fast charging conditions. Its thickness has a low expansion rate after storage at 80°C for 8 hours, indicating that the secondary battery has good high-temperature stability. Among them, Figure 6 shows the Raman spectrum of Example 3-3. It can be seen from Figure 6 that in the Raman spectrum of the high-kinetic negative electrode material, its I d / I g A higher value indicates that it has good surface activity.

[0195] The type of positive electrode active material usually affects the cycle performance and high temperature stability of the secondary battery. d / I g The secondary battery with a value within the scope of this application has a high capacity retention rate at a charging rate of 10C, indicating that the secondary battery has good cycle performance under fast charging conditions, and its thickness has a low expansion rate after storage at 80°C for 8h, indicating that the secondary battery has good high-temperature stability.

[0196] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0197] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0198] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, wherein: An electrode assembly is included, wherein the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet includes a positive electrode active material layer, wherein the positive electrode active material layer includes a positive electrode active material, wherein the negative electrode sheet includes a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode active material; The coating weight of the positive electrode active material layer is W z The coating weight of the negative electrode active material layer is W f , W z and W f Between: 1.6W f ≤W z ≤2.2W f 、3.25mg / cm 2 ≤W f ≤5.84mg / cm 2 ; The Dv99 of the positive electrode active material is 27 μm to 33 μm, and the Dv99 of the negative electrode active material is 23 μm to 28 μm; The isolation film comprises an isolation film substrate, a first bonding coating layer and a second bonding coating layer, wherein the first bonding coating layer and the second bonding coating layer are respectively disposed on both sides of the isolation film substrate; The first bonding coating layer comprises a first polymer binder, and the average particle size of the first polymer binder is 0.3 μm to 3 μm; the second bonding coating layer comprises a second polymer binder, and the average particle size of the second polymer binder is 10 μm to 38 μm.

2. The secondary battery according to claim 1, wherein The first bonding coating is disposed on a side of the separator substrate close to the negative electrode plate, and the second bonding coating is disposed on a side of the separator substrate close to the positive electrode plate.

3. The secondary battery according to claim 1, wherein The Dv50 of the positive electrode active material is 10 μm to 15 μm, and the Dv50 of the negative electrode active material is 7 μm to 12 μm.

4. The secondary battery according to claim 1, wherein 6.49mg / cm 2 ≤W z ≤11.69mg / cm 2 。 5. The secondary battery according to claim 1, wherein The positive electrode active material has a Dv99 of 28 μm to 31 μm and a Dv50 of 11 μm to 13 μm, and the negative electrode active material has a Dv99 of 24 μm to 26 μm and a Dv50 of 8 μm to 11 μm.

6. The secondary battery according to claim 1, wherein The thickness of the first bonding coating layer is 0.2 μm to 4 μm, and the thickness of the second bonding coating layer is 5 μm to 20 μm.

7. The secondary battery according to claim 1, wherein The single-sided coating weight of the first bonding coating is 1×10 -4 mg / mm 2 Up to 1×10 -3 mg / mm 2 The single-sided coating weight of the second bonding coating is 4×10 -4 mg / mm 2 Up to 2×10 -3 mg / mm 2 .

8. The secondary battery according to claim 1, wherein The coverage rate of the first polymer binder in the first bonding coating layer per unit area is 40% to 60%.

9. The secondary battery according to claim 1, wherein The first polymer binder includes a core-shell structure first polymer binder or a non-core-shell structure first polymer binder, the core of the core-shell structure first polymer binder includes at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid or maleic acid, the shell of the core-shell structure first polymer binder includes at least one of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, ethyl chloromethylacrylate, chlorostyrene, fluorostyrene, methylstyrene, acrylonitrile or methacrylonitrile; the non-core-shell structure first polymer binder includes at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, fluorostyrene, chlorostyrene or propylene.

10. The secondary battery according to claim 1, wherein The coverage rate of the second polymer binder in the second bonding coating layer per unit area is 40% to 60%.

11. The secondary battery according to claim 1, wherein The polymerizable monomer of the second polymer binder includes at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, allyl chloride, acrylic acid, methyl acrylate, butyl acrylate, chlorostyrene, fluorostyrene, ethyl acrylate, ethyl methacrylate, methyl methacrylate, butyl methacrylate, ethyl chloromethylacrylate, styrene, butadiene or acrylonitrile.

12. The secondary battery according to claim 1, wherein The second polymer binder includes a core-shell structured second polymer binder or a non-core-shell structured second polymer binder, wherein the polymerized monomer of the shell of the core-shell structured second polymer binder includes at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, styrene, butadiene, acrylonitrile, acrylic acid, methyl acrylate or butyl acrylate, and the core of the core-shell structured second polymer binder includes at least one of ethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate or ethyl chloromethylacrylate; the polymerized monomer of the non-core-shell structured second polymer binder includes at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, propylene, chlorostyrene, fluorostyrene, vinylidene chloride, vinylidene fluoride, hexafluoropropylene, vinyl chloride or allyl chloride.

13. The secondary battery according to claim 1, wherein The positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

14. The secondary battery according to claim 1, wherein The positive electrode active material further includes a non-metallic element, and the non-metallic element includes at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur.

15. The secondary battery according to claim 1, wherein The negative electrode active material includes at least one of a carbon-based material, a silicon-based material or a tin-based material, the carbon-based material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon or mesophase carbon microspheres, the silicon-based material includes at least one of a silicon material, a silicon-carbon material or a silicon-oxygen material, and the tin-based material includes at least one of elemental tin, a tin alloy or a tin oxide.

16. The secondary battery according to claim 15, wherein The carbon-based material is tested by Raman with a peak intensity ratio of d peak to g peak. d / I g Satisfy: 0.1≤I d / I g ≤1. 17 . An electric device comprising the secondary battery according to claim 1 .

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