Secondary battery and electrical device

Abstract

A secondary battery and an electrical device. In the secondary battery, a positive electrode sheet comprises a positive electrode active material, and a negative electrode sheet comprises a negative electrode active material, the Dv99 of the positive electrode active material being 27μm to 33μm, and the Dv99 of the negative electrode active material being 23μm to 28μm. A separator comprises a separator base material, a first bonding coating and a second bonding coating, the first bonding coating and the second bonding coating being arranged on two sides of the separator base material respectively. The first bonding coating comprises a first polymer binder, the average particle size of the first polymer binder being 0.3μm to 3μm. The second bonding coating comprises a second polymer binder, the average particle size of the second polymer binder being 10μm to 38μm. An electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the organic solvent comprises a chain carboxylic ester, and, on the basis of the mass of the electrolyte, the mass percentage content of the chain carboxylic ester is 6% to 56%. The secondary battery has good cycle dynamic performance and high-temperature stability.

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 has increasingly higher requirements for their charging speed, and the charging rate of lithium-ion batteries has continued to increase. Consumer demand has gradually increased from 1C to more than 5C. However, it is difficult to balance the charging rate and high temperature (temperature ≥ 60°C) stability of super-fast charging (5C≤charging rate≤15C) lithium-ion batteries. Therefore, how to improve the cycle dynamics performance of lithium-ion batteries while taking into account the high temperature stability of 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 improves the cycle dynamics performance of the secondary battery while taking into account the high-temperature stability 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, wherein the secondary battery includes an electrode assembly and an electrolyte, the electrode assembly includes a positive electrode plate, a negative electrode plate and a separator, the positive electrode plate includes a positive electrode active material, the negative electrode plate includes a negative electrode active material, the Dv99 of the positive electrode active material is 27μm to 33μm, and the Dv99 of the negative electrode active material is 23μm to 28μm; the separator includes a separator 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 separator substrate; the first bonding coating contains a first polymer binder, and the average particle size of the first polymer binder is 0.3μm to 3μm; the second bonding coating contains a second polymer binder, and the average particle size of the second polymer binder is 10μm to 38μm; the electrolyte includes an organic solvent, a lithium salt and an additive, the organic solvent includes a chain carboxylic acid ester; based on the mass of the electrolyte, the mass percentage of the chain carboxylic acid ester is 6% to 56%. This application controls the Dv99 of the positive and negative active materials within the above-mentioned ranges, so that lithium ions have a shorter transmission path within the positive / negative active materials and a smaller transmission tortuosity within the positive / negative electrode sheets during transmission, thereby reducing the concentration polarization of the secondary battery and thus providing the secondary battery with good cycle kinetics. This application controls the mass percentage of the chain carboxylic acid ester in the electrolyte within the above-mentioned range, so that lithium ions have a faster transmission speed in the electrolyte, thereby reducing the electrochemical polarization and concentration polarization of the secondary battery, reducing the impedance of the secondary battery, and reducing the charging temperature rise and charging time during fast charging of the secondary battery, thereby providing the secondary battery with good cycle kinetics and fast charging performance. That is, through the high kinetic design of the positive and negative electrode material particle size and electrolyte composition, a high-rate chemical system of the secondary battery is guaranteed. However, the high kinetic design makes it easy for side reactions to occur between the positive and negative electrode active materials and the electrolyte, especially at high temperatures, where violent side reactions produce a large amount of gas, resulting in poor high-temperature performance of the secondary battery. 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. The first bonding coating side of the isolation membrane has high bonding force, which can strengthen the bonding force between the isolation membrane and the positive / negative electrode sheets, strengthen the interface between the isolation membrane and the positive / negative electrode sheets, inhibit gas production under high temperature conditions, and reduce the probability of the secondary battery expanding due to excessive gas production, so as to improve high-temperature stability. The second bonding coating side of the isolation membrane can generate an electrolyte flow channel and store electrolyte, thereby 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 super-fast charging state, thereby ensuring the rate and cycle performance of the secondary battery.This application combines the isolation membrane, Dv99 of the positive electrode active material, Dv99 of the negative electrode active material and the electrolyte, so that there is a good synergistic effect between the isolation membrane, Dv99 of the positive electrode active material, Dv99 of the negative electrode active material and the electrolyte, which can improve the cycle dynamics performance of the secondary battery while taking into account the high temperature stability of the secondary battery.

[0007] In one embodiment of the present application, the Dv99 of the positive electrode active material is 28 μm to 31 μm, and / or the Dv99 of the negative electrode active material is 24 μm to 26 μm. By regulating the Dv99 of the positive electrode active material and / or the negative electrode active material within the above range, the Dv99 range of the positive electrode active material and / or the negative electrode active material is more optimal, which is conducive to further improving the cycle dynamics performance and high temperature stability of the secondary battery.

[0008] In one embodiment of the present application, the average particle size of the first polymer binder is 0.6 μm to 1.6 μm; and / or the average particle size of the second polymer binder is 20 μm to 30 μm. Controlling the average particle size of the first polymer binder and / or the average particle size of the second polymer binder within the above ranges is beneficial for achieving a high energy density in the secondary battery while balancing cycling kinetics and high-temperature stability.

[0009] In one embodiment of the present application, 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. 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 kinetics and high-temperature stability.

[0010] In one embodiment of the present application, the first adhesive coating is arranged on the side of the separator substrate close to the negative electrode sheet, and the second adhesive coating is arranged on the side of the separator substrate close to the positive electrode sheet. By setting the positional relationship between the first adhesive coating and the second adhesive coating in the separator and the negative electrode sheet and the positive electrode sheet, the secondary battery can further improve its cycle dynamics 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, so the first adhesive coating with smaller separator particles is arranged on the negative electrode sheet side, which can shorten the lithium ion transmission path during the charging process and achieve faster charging speed.

[0011] In one embodiment of the present application, the thickness of the first adhesive coating is 0.2 μm to 4 μm, and the thickness of the second adhesive coating is 5 μm to 20 μm. The first adhesive coating has a smaller particle size and stronger bonding force. Ensuring its thickness is between 0.2 μm and 4 μm can maximize the energy density while ensuring bonding force, while shortening the lithium ion transmission path in the active material layer corresponding to the first adhesive coating. The second adhesive coating has a larger particle size, which can form a channel for electrolyte circulation. Setting it between 5 μm and 20 μm can improve the energy density while ensuring the flow and wettability of the electrolyte.

[0012] In one embodiment of the present application, the single-sided coating weight of the first bonding coating is 0.0001 mg / mm 2 to 0.001 mg / mm 2 The single-sided coating weight of the second bonding coating is 0.0004 mg / mm 2 to 0.002 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 characteristics of the secondary battery.

[0013] In one embodiment of the present application, the coverage of the first polymer binder per unit area of ​​the first bonding coat is 40% to 60%. Controlling the coverage of the first polymer binder per unit area of ​​the first bonding coat within this range allows the secondary battery to achieve both cyclic kinetic performance and high-temperature stability while maintaining low production costs. This fully utilizes the high bonding properties of the first bonding coat, facilitates bonding between the separator and the electrode, and allows for faster lithium ion transmission, thereby further improving the secondary battery's kinetic performance.

[0014] In one embodiment of the present application, the first polymer binder is a core-shell structure, the first polymer binder includes a first shell and a first core, the polymerization monomer of the first shell 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, and the polymerization monomer of the first core includes at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid or maleic acid; or, the first polymer binder is a non-core-shell structure, and the polymerization monomer of the 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.

[0015] In one embodiment of the present application, the coverage of the second polymer binder per unit area of ​​the second bonding coat is 40% to 60%. By regulating the coverage of the second polymer binder per unit area of ​​the second bonding coat within the above range, the second polymer binder allows a large gap between the second bonding coat and the positive electrode or negative electrode, thereby fully realizing an electrolyte flow channel between the electrode and the separator. When the electrolyte has good flow and wettability in the electrode and the separator, the second bonding coat has an appropriate thickness, thereby reducing the risk of energy density loss caused by an increase in the volume of the fast-charging secondary battery due to excessive thickness. As a result, the secondary battery can have a low production cost and a high energy density while taking into account both cycle dynamics performance and high-temperature stability.

[0016] In one embodiment of the present application, the second polymer binder has a core-shell structure, the second polymer binder includes a second shell and a second core, the polymerized monomers of the second shell include at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, styrene, butadiene, acrylonitrile, acrylic acid, methyl acrylate, or butyl acrylate, and the polymerized monomers of the second core include at least one of ethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate, or ethyl chloromethylacrylate; or, the second polymer binder has a non-core-shell structure, the polymerized 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, styrene, butadiene, or acrylonitrile. The selection of the above-mentioned second polymer binder can provide a large gap between the second bonding coating and the positive / negative electrode sheet.

[0017] In one embodiment of the present application, the chain carboxylate includes at least one of methyl formate, methyl acetate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, methyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl butyrate, n-propyl butyrate, propyl isobutyrate, n-pentyl butyrate, n-pentyl isobutyrate, n-butyl butyrate, isobutyl isobutyrate, or n-pentyl valerate. The above-mentioned chain carboxylate has high conductivity and low viscosity, and is convenient for lithium ion transport. The use of the above-mentioned chain carboxylate can enable the secondary battery to have good cycle dynamics and high-temperature stability.

[0018] In one embodiment of the present application, the mass percentage of the chain carboxylate is 18% to 40% based on the mass of the electrolyte. By regulating the mass percentage of the chain carboxylate within this range, lithium ions are transported more rapidly in the electrolyte, thereby further improving the cycling kinetics of the secondary battery while maintaining good high-temperature stability.

[0019] In one embodiment of the present application, the organic solvent further comprises at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, or tetrahydrofuran; and the weight percentage of the organic solvent is 60% to 90% based on the weight of the electrolyte. Further, selecting the above organic solvents and regulating the weight percentage of the organic solvents within the above ranges facilitates the secondary battery to have good cycling kinetics and high-temperature stability.

[0020] In one embodiment of the present application, the additive includes 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; based on the mass of the electrolyte, the mass percentage of the additive is 2% to 20%.

[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 elemental silicon, 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 cycling kinetics 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: 0.2≤Id / I g ≤1.0. 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 dynamics performance of secondary batteries on the basis of good high-temperature stability.

[0023] 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 cycling kinetics while maintaining high-temperature stability.

[0024] 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.

[0025] The second aspect of the present application provides an electric device, which includes the secondary battery described in any of the above embodiments. Therefore, the electric device has good performance.

[0026] Beneficial effects of this application:

[0027] The present application provides a secondary battery and an electrical device. The secondary battery regulates the mass percentages of the positive electrode active material (Dv99), the negative electrode active material (Dv99), and the chain carboxylate in the electrolyte within the ranges of the present application. Furthermore, a first bonding coating layer and a second bonding coating layer are provided on either side of a separator, respectively, with the average particle size range of the first polymer binder in the first bonding coating layer and the average particle size range of the second polymer binder in the second bonding coating layer being limited to within the aforementioned ranges of the present application. This allows for a good synergistic effect between the separator, the positive electrode active material, the negative electrode active material, and the electrolyte. This results in a shorter lithium ion transport path within the positive and negative electrode active materials, a smaller transport tortuosity within the positive and negative electrode sheets, and a faster transport speed in the electrolyte, thereby reducing concentration polarization and electrochemical polarization in the secondary battery. Furthermore, a wider electrolyte flow channel and stronger interfacial adhesion are provided between the separator and the positive or negative electrode sheet, enabling the secondary battery to maintain high-temperature stability while improving cycle kinetics. The electrical device of the present application has good performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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.

[0029] 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;

[0030] 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;

[0031] 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;

[0032] 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;

[0033] 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;

[0034] FIG6 is a Raman spectrum of the negative electrode of Example 3-3. DETAILED DESCRIPTION

[0035] 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.

[0036] 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.

[0037] The first aspect of the present application provides a secondary battery, wherein the secondary battery includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode sheet, a negative electrode sheet, and a separator, the separator being disposed between the positive electrode sheet and the negative electrode sheet to separate the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive electrode active material, the negative electrode sheet includes a negative electrode active material, the Dv99 of the positive electrode active material is 27μm to 33μm, and the Dv99 of the negative electrode active material is 23μm to 28μm. The separator includes a separator substrate, a first bonding coating, and a second bonding coating, the first bonding coating and the second bonding coating being disposed on both sides of the separator substrate, respectively. The first bonding coating comprises a first polymer binder having an average particle size of 0.3μm to 3μm; the second bonding coating comprises a second polymer binder having an average particle size of 10μm to 38μm. The electrolyte includes an organic solvent, a lithium salt and an additive. The organic solvent includes a chain carboxylate. The mass percentage of the chain carboxylate is 6% to 56% based on the mass of the electrolyte.

[0038] For example, the Dv99 of the positive electrode active material is 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm or any value between any two of the above numerical ranges. 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 and the positive electrode active material particles being unevenly distributed. As the number of electrolyte contact interfaces 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 the 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 kinetics performance of the secondary battery.

[0039] For example, the Dv99 of the negative electrode active material is 23μm, 24μm, 25μm, 26μm, 27μm, 28μm or any value between any two of the above numerical ranges. 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 particles of the negative electrode active material 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 and the agglomeration of the negative electrode active material particles. As the number of electrolyte contact interfaces 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 the 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 kinetics 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] For example, the average particle diameter of the first polymer binder is 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or any numerical value between any two numerical ranges mentioned above. The average particle diameter of the first polymer binder is less than 0.3 μm, and the average particle diameter of the first polymer binder is too small. When preparing the first bonding coat slurry, each particle of the first polymer binder is easily agglomerated. Like this, the probability that the first polymer binder is uniformly dispersed in the first bonding coat slurry is extremely small, and the distribution of the first polymer binder in the first bonding coat formed is uneven, which will affect the cohesive force of the first bonding coat. The average particle diameter of the first polymer binder is greater than 3 μm, and the average particle diameter of the first polymer binder is too large. The gap between each particle of the first polymer binder will be too large, causing poor cycle performance, and the average particle diameter of the first polymer binder is too large to increase the thickness of the first bonding coat, thereby increasing the volume of the secondary battery and causing its energy density to be lost.

[0042] For example, the average particle size of the second polymer binder is 10 μm, 12 μm, 20 μm, 25 μm, 28 μm, 30 μm, 38 μm, or any value between any two of the above numerical ranges. 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 electrode sheet or the negative electrode sheet will be too small, and the transmission channel of the electrolyte will be too narrow, which will affect the transmission of the electrolyte and thus affect the cycle performance and dynamic performance of the secondary battery. The average particle size of the second polymer binder is greater than 38 μm. If the average particle size of the second polymer binder is too large, the thickness of the second bonding coating layer will increase, thereby increasing the volume of the secondary battery and causing a loss in its energy density.

[0043] For example, based on the mass of the electrolyte, the mass percentage of the chain carboxylate is 6%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 56%, or any value between any two of the above numerical ranges. Chain carboxylate has the characteristics of high conductivity, low viscosity, easy lithium ion transport, and high dynamics of the electrolyte. If the mass percentage of the chain carboxylate is less than 6%, the content of the chain carboxylate in the electrolyte is too low to fully exert its own characteristics. If the mass percentage of the chain carboxylate is greater than 56%, the content of the chain carboxylate in the electrolyte is too high, and the content of lithium salt and additives in the electrolyte is reduced. Insufficient lithium salt content will affect the charge and discharge performance of the secondary battery. Insufficient additive content will make it difficult for the additive to fully exert its own function, which will affect the corresponding performance of the secondary battery and the additive.

[0044] Overall, this application controls the Dv99 of the positive and negative active materials within the above-mentioned ranges, so that lithium ions have a shorter transmission path within the positive / negative active materials and a smaller transmission tortuosity within the positive / negative electrode sheets during transmission, thereby reducing the concentration polarization of the secondary battery and thus providing the secondary battery with good cycle kinetics. This application controls the mass percentage of the chain carboxylic acid ester in the electrolyte within the above-mentioned range, so that lithium ions have a faster transmission speed in the electrolyte, thereby reducing the electrochemical polarization and concentration polarization of the secondary battery, reducing the impedance of the secondary battery, and reducing the charging temperature rise and charging time during fast charging of the secondary battery, thereby providing the secondary battery with good cycle kinetics and fast charging performance. That is, through the high kinetic design of the positive and negative active material particle size and electrolyte composition, a high-rate chemical system of the secondary battery is guaranteed. However, the high kinetic design makes it easy for side reactions to occur between the positive and negative active materials and the electrolyte, especially at high temperatures, where violent side reactions produce large amounts of gas, resulting in poor high-temperature performance of the secondary battery. 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. The first bonding coating side of the isolation membrane has high bonding force, which can strengthen the bonding force between the isolation membrane and the positive / negative electrode sheets, strengthen the interface between the isolation membrane and the positive / negative electrode sheets, inhibit gas production under high temperature conditions, and reduce the probability of the secondary battery expanding due to excessive gas production, so as to improve high-temperature stability. The second bonding coating side of the isolation membrane can generate an electrolyte flow channel and store electrolyte, thereby 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 super-fast charging state, thereby ensuring the rate and cycle performance of the secondary battery. This application combines the isolation membrane, Dv99 of the positive electrode active material, Dv99 of the negative electrode active material and the electrolyte, so that there is a good synergistic effect between the isolation membrane, Dv99 of the positive electrode active material, Dv99 of the negative electrode active material and the electrolyte, which can improve the cycle dynamics performance of the secondary battery while taking into account the high temperature stability of the secondary battery.

[0045] In one embodiment of the present application, the chain carboxylate includes at least one of methyl formate, methyl acetate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, methyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl butyrate, n-propyl butyrate, propyl isobutyrate, n-pentyl butyrate, n-pentyl isobutyrate, n-butyl butyrate, isobutyl isobutyrate, or n-pentyl valerate. The above-mentioned chain carboxylate has high conductivity and low viscosity, and is convenient for lithium ion transport. The use of the above-mentioned chain carboxylate can enable the secondary battery to have good cycle dynamics and high-temperature stability.

[0046] In one embodiment of the present application, the Dv99 of the positive electrode active material is 28 μm to 31 μm. For example, the Dv99 of the positive electrode active material is 28 μm, 29 μm, 30 μm, 31 μm, or any value between any two of the above ranges. By regulating the Dv99 of the positive electrode active material within the above range, the Dv99 range of the positive electrode active material is more optimal, which is conducive to further improving the cycle dynamics performance and high-temperature stability of the secondary battery.

[0047] In one embodiment of the present application, the Dv99 of the negative electrode active material is 24 μm to 26 μm. For example, the Dv99 of the negative electrode active material is 24 μm, 25 μm, 26 μm, or any value between any two of the above ranges. By regulating the Dv99 of the negative electrode active material within the above range, the Dv99 range of the negative electrode active material is more optimal, which is conducive to further improving the cycle dynamics performance and high-temperature stability of the secondary battery.

[0048] In one embodiment of the present application, the Dv99 of the positive electrode active material is 28μm to 31μm, and the Dv99 of the negative electrode active material is 24μm to 26μm. For example, the Dv99 of the positive electrode active material is 28μm, 29μm, 30μm, 31μm or any value between any two of the above numerical ranges. The Dv99 of the negative electrode active material is 24μm, 25μm, 26μm or any value between any two of the above numerical ranges. By regulating the Dv99 of the positive electrode active material and the negative electrode active material within the above range, the Dv99 range of the positive electrode active material and the negative electrode active material is better, which is conducive to further improving the cycle dynamics performance and high temperature stability of the secondary battery.

[0049] In this application, Dv99 means the particle size at which 99% of the volume accumulation is achieved, starting from the small particle size side, in the volume-based particle size distribution. The above-mentioned "particles" in this application can be particles of positive electrode active materials or particles of negative electrode active materials. This application does not particularly limit the method for regulating the Dv99 of positive electrode active materials and negative electrode active materials, as long as the purpose of this application can be achieved. For example, this can be achieved by directly purchasing positive electrode active materials and negative electrode active materials whose Dv99 is within the scope of this application, or by crushing, grinding or ball milling.

[0050] In one embodiment of the present application, the average particle size of the first polymer binder is 0.6 μm to 1.6 μm. In another embodiment of the present application, the average particle size of the second polymer binder is 20 μm to 30 μm. In yet another embodiment of the present application, the average particle size of the first polymer binder is 0.6 μm to 1.6 μm, and the average particle size of the second polymer binder is 20 μm to 30 μm. For example, the average particle size of the first polymer binder is 0.6 μm, 0.8 μm, 1.0 μm, 1.6 μm, or any value between any two of the above numerical ranges. For example, the average particle size of the second polymer binder is 20 μm, 22 μm, 25 μm, 27 μm, 30 μm, or any value between any two of the above numerical ranges. Regulating the average particle size of the first polymer binder within the above range is conducive to uniform distribution of the first polymer binder in the first bonding coat, and there is a suitable gap between each particle of the first polymer binder, so that the high-binder coating has a stronger bonding force. It is also conducive to regulating the thickness of the first bonding coat within a suitable range, so that the secondary battery has a higher energy density while taking into account both cycle dynamics performance and high-temperature stability. Regulating the average particle size of the second polymer binder within the above range provides a suitable gap between the separator and the positive electrode sheet and / or the negative electrode sheet, which is conducive to the transmission of the electrolyte. It is also conducive to regulating the thickness of the second bonding coat within a suitable range, so that the secondary battery has a higher energy density while taking into account both cycle dynamics performance and high-temperature stability.

[0051] In one embodiment of the present application, 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. For example, the Dv50 of the positive electrode active material is 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any value between any two of the above numerical ranges. The Dv50 of the negative electrode active material is 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any value between any two of the above numerical ranges. 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 dynamics and high temperature stability.

[0052] 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. As shown in Figure 1, the first bonding coating 32 is arranged on the side of the separator substrate 31 close to the negative electrode sheet 20, and the second bonding coating 33 is arranged on the side of the separator substrate 31 close to the positive electrode sheet 10. 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 cycle dynamics performance of the secondary battery is further improved 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 charging process of the secondary battery mainly involves the embedding of lithium ions in the negative electrode. Therefore, the first bonding coating with smaller separator particles is arranged on the side close to the negative electrode sheet, which can shorten the lithium ion transmission path during the charging process and achieve faster charging speed.

[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 any value between any two of the above numerical ranges. The particle size of the first polymer binder in the first bonding coating is relatively 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 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 any value between any two of the above numerical ranges. 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 thickness being too large. In this way, the secondary battery can have good energy density based on both cycle dynamics performance and high temperature stability.

[0055] In one embodiment of the present application, the single-sided coating weight of the first bonding coating is 0.0001 mg / mm 2 to 0.001 mg / mm 2 For example, the single-sided coating weight of the first bonding coating is 0.0001 mg / mm 2 , 0.0002mg / mm 2 , 0.0003mg / mm 2 , 0.0004mg / mm 2 , 0.0005mg / mm 2 , 0.0006mg / mm 2 , 0.0007mg / mm 2 , 0.0008mg / mm 2 , 0.0009mg / mm 2 , 0.001mg / mm2 Or any value between any two of the above numerical ranges. Controlling 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 electrode and separator, and ensure the high-temperature stability and mechanical reliability of the secondary battery. It can also reduce the risk of energy density loss caused by the increase in secondary battery volume due to excessive single-sided coating weight. In this way, the secondary battery can have good energy density while taking into account both cycle dynamics performance and high-temperature stability.

[0056] In one embodiment of the present application, the single-sided coating weight of the second bonding coating is 0.0004 mg / mm 2 to 0.002 mg / mm 2 For example, the coating weight of the second adhesive coating layer on one side is 0.0004 mg / mm 2 , 0.0008mg / mm 2 , 0.0012mg / mm 2 , 0.0016mg / mm 2 , 0.002mg / 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.

[0057] 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 any value between any two of the above numerical ranges. 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 to the bonding of the isolation membrane and the pole piece, the lithium ions have a faster transmission speed, which is more conducive to making the secondary battery have good dynamic performance.

[0058] In one embodiment of the present application, the first polymer binder is a core-shell structure, the first polymer binder includes a first shell and a first core, the polymerized monomer of the first shell 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, and the polymerized monomer of the first core includes at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid or maleic acid. The above-mentioned first polymer binder is applied to the first bonding coating to enable the first bonding coating to have high bonding strength.

[0059] In one embodiment of the present application, the first polymer binder has a non-core-shell structure, and the polymerized monomer of the 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 bonding strength.

[0060] 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 first bonding coating layer slurry and prevent the sedimentation of the components in the first bonding coating layer 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 layer slurry. The wetting agent is applied to the first bonding coating layer to reduce the surface energy of the first bonding coating layer slurry and prevent the first bonding coating layer 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%.

[0061] In one embodiment of the present application, the coverage Cr2 of the second polymer binder per unit area in the second bonding coat is 40% to 60%. For example, the coverage of the second polymer binder per unit area in the second bonding coat is 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60% or any value between any two of the above numerical ranges. The coverage of the second polymer binder per unit area in the second bonding coat is regulated within the above range, and the second polymer binder provides a large gap between the second bonding coat and the positive electrode sheet or the negative electrode sheet, so that 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 excessive thickness. In this way, the secondary battery can also improve its energy density while taking into account both cycle dynamics performance and high temperature stability.

[0062] In one embodiment of the present application, the second polymer binder has a core-shell structure, comprising a second outer shell and a second inner core. The monomers of the second outer shell include at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, styrene, butadiene, acrylonitrile, acrylic acid, methyl acrylate, or butyl acrylate, and the monomers of the second inner core include at least one of ethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate, or ethyl chloromethylacrylate. The use of these second polymer binders allows for a large gap between the second bonding coating and the positive / negative electrode sheets.

[0063] In one embodiment of the present application, the second polymer binder has a non-core-shell structure, and the 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, styrene, butadiene, or acrylonitrile. The use of these second polymer binders allows for a large gap between the second bonding coating and the positive / negative electrode sheets.

[0064] In one embodiment of the present application, the second bonding coating includes a second polymer binder and an auxiliary binder. The auxiliary binder is applied to the second bonding coating, 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, as long as the purpose of the present application can be achieved. For example, based on the mass of the second bonding coating, the mass percentage of the second polymer binder is 85% to 95%, and the mass percentage of the auxiliary binder is 5% to 15%.

[0065] 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.

[0066] 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 layers of ceramic coating 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 layers of ceramic coating 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 cycle dynamics and high-temperature stability. In the present application, it is preferred that the second bonding coating 33 faces the positive electrode plate 10, and the ceramic coating 34 is arranged between the isolation membrane substrate 31 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 improve 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.

[0067] 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 has no particular limitation on the thickness of the ceramic coating. For example, the thickness of the ceramic coating may be 0.5 μm to 6 μm.

[0068] In this application, Dv50 refers to the particle size at which 50% of the volume is accumulated, starting from the small particle size side, in the volume-based particle size distribution. The above-mentioned "particles" in this application can be positive electrode active materials or negative electrode active materials. This application does not particularly limit the method for regulating the Dv50 of positive electrode active materials and negative electrode active materials, as long as the purpose of this application can be achieved. For example, this can be achieved by directly purchasing positive electrode active materials and negative electrode active materials whose Dv50 is within the range of this application, or by crushing, grinding or ball milling.

[0069] In the present application, the average particle size can be understood as an equivalent diameter, which generally refers to the diameter of a sphere with the same volume as an object with an irregular shape. In the present application, the cross section of the electrode is obtained, the area of ​​the particle of the object to be measured on the cross section is measured, and then the diameter of a circle with the same area as the area is used as the equivalent diameter of the particle of the object to be measured. The present application has no special restrictions on the method for regulating the average particle size of the first polymer binder, the average particle size of the second polymer binder, and the average particle size of the ceramic particles, as long as the purpose of the present application can be achieved. For example, it can be achieved by directly purchasing the first polymer binder, the second polymer binder, and the ceramic particles whose average particle size is within the range of the present application, or by crushing, grinding, or ball milling.

[0070] The present application does not particularly limit the isolation film substrate, as long as it can achieve the purpose of this application. For example, the structure of the isolation film 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 the isolation film substrate includes at least one of polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET). The thickness of the isolation film substrate can be 3 μm to 20 μm.

[0071] In one embodiment of the present application, the weight percentage of the chain carboxylate is 18% to 40% based on the weight of the electrolyte. For example, the weight percentage of the chain carboxylate is 18%, 20%, 25%, 30%, 35%, 40%, or any value between any two of the above ranges. By regulating the weight percentage of the chain carboxylate within the above range, lithium ions can be transported faster in the electrolyte, thereby further improving the cycling kinetics of the secondary battery while maintaining good high-temperature stability.

[0072] In one embodiment of the present application, the organic solvent further comprises at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, or tetrahydrofuran. These organic solvents have good stability at high temperatures and excellent lithium ion transport capabilities at low temperatures. Adding these organic solvents to the electrolyte can further improve the high-temperature stability, cycling kinetics, and post-storage capacity retention of the secondary battery.

[0073] In one embodiment of the present application, the mass percentage of the organic solvent is 60% to 90% based on the mass of the electrolyte. For example, the mass percentage of the organic solvent is 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any value between any two of the above ranges based on the mass of the electrolyte. Regulating the mass percentage of the organic solvent within the above range is beneficial to improving the solubility of the additive and the lithium salt, so that the electrolyte has a lower viscosity and higher conductivity, which is beneficial to the migration of lithium ions in the electrolyte, thereby enabling the secondary battery to have good cycle dynamics and high temperature stability.

[0074] In one embodiment of the present application, the mass percentage of the lithium salt is 8% to 20% based on the mass of the electrolyte. For example, the mass percentage of the lithium salt is 8%, 10%, 12%, 14%, 16%, 18%, 20% or any value between any two of the above numerical ranges. The present application does not particularly limit the type of lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt includes but is not limited to 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.

[0075] In one embodiment of the present application, the mass percentage of the additive is 2% to 20% based on the mass of the electrolyte. For example, the mass percentage of the additive is 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20% or any value between any two of the above numerical ranges. The present application does not particularly limit the type of additive, 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.

[0076] 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 elemental silicon, 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 high 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, so that the secondary battery has good cycle kinetics while maintaining high temperature stability.

[0077] 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: 0.2≤I d / I g ≤1.0. For example, I d / I gis 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 or any value between any two of the above numerical ranges. This indicates that the surface of the carbon-based material contains amorphous carbon. The presence of amorphous carbon on the surface of the carbon-based material can enhance the electrochemical activity of the carbon-based material, making the embedding of lithium ions smoother during the cycle of the secondary battery, 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 d / I g The application of high-value carbon-based materials in secondary batteries is beneficial to further improve the cycle dynamics performance of secondary batteries on the basis of good high-temperature stability.

[0078] 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 -1 The peak of g is the shift range of 1530cm in the Raman spectrum of carbon-based material particles. -1 to 1630cm -1 Peak.

[0079] 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.

[0080] The present application does not particularly limit 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: mixing the carbon-based material and amorphous carbon uniformly, heating to 500°C to 1500°C, and then maintaining the temperature for 10 hours to 20 hours to obtain a carbon-based material with amorphous carbon coated on the surface.

[0081] 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 materials, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate. The chemical formula of the above-mentioned "lithium-rich manganese-based materials" is LiMnO·LiMO, where M may include Ni, Co, or Mn. The above-mentioned types of positive electrode active materials have high surface activity and are applied to secondary batteries to increase the 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, so that the secondary battery has good cycle dynamics performance on the basis of high temperature stability.

[0082] 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 any value between any two of the above numerical ranges. 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.

[0083] 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. 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 particularly limit the type of positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector can include but is not limited to aluminum foil or aluminum alloy foil. The positive electrode active material layer of the present application includes the positive electrode active material described in the above embodiments. In the present application, there is no particular limitation 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, and further, the thickness of the positive electrode current collector can be 6μm to 18μm. The thickness of the positive electrode active material layer is 30μm to 120μm.

[0084] Optionally, the positive electrode active material layer may further include a positive electrode conductor and a positive electrode binder. The present application has no particular restrictions on the types of positive electrode conductors and positive electrode binders in the positive electrode active material layer, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the mass ratio of the positive electrode active material, the positive electrode conductor, and the 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 the present application can be achieved. For example, the mass ratio of the positive electrode active material, the positive electrode conductor, and the positive electrode binder in the positive electrode active material layer is (95-98): (0.5-3.5): (1.5-3.4).

[0085] 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 above-mentioned "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 type of negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector includes but is not limited to copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam or copper foam. The negative electrode active material layer of the present application includes the negative electrode active material described in the above embodiments. In the present application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 6μm to 10μm, and the thickness of the negative electrode active material layer is 30μm to 130μm.

[0086] Optionally, the negative electrode active material layer may also include at least one of a negative electrode conductor, a dispersant, and a negative electrode binder. The present application does not particularly limit the types of the negative electrode conductor, dispersant, and negative electrode binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved. The present application does not particularly limit the mass ratio of the negative electrode active material, the negative electrode conductor, the dispersant, and the 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 mass ratio of the negative electrode active material, the negative electrode conductor, the dispersant, and the negative electrode binder in the negative electrode active material layer is (96-98):(0-2):(0-1.5):(1.0-1.9).

[0087] 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.

[0088] 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.

[0089] The secondary battery of the present application can be used under super-fast charging conditions, specifically, can be used under conditions of 5C to 15C. For example, the charging rate of the secondary battery can be 5C, 6C, 7C, 8C, 9C, 10C, 11C, 12C, 13C, 14C, 15C or any rate between any two of the above rate ranges.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] The second aspect of the present application provides an electric device, which includes the secondary battery described in any of the above embodiments. Therefore, the electric device has good performance.

[0098] 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.

[0099] Example

[0100] 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.

[0101] Test methods and equipment:

[0102] Relevant particle size tests:

[0103] 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 equivalent diameters of 10 first polymer binder or second polymer binder particles are randomly selected and 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 two surfaces 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. It is worth noting that since the particles bonded by the first polymer binder and the second polymer will deform under the pressure of cold pressing, hot pressing, etc. 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 obtained by measuring 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 layer and the second bonding layer.

[0104] The average particle size of the ceramic particles on the isolation membrane can be determined by observing the cross section of the isolation membrane that has been sliced ​​by argon ion polishing or embedding using a SEM, measuring the diameters of 10 ceramic particles, and calculating the average value.

[0105] The Dv50 and Dv99 of the positive and negative active materials were measured using a laser particle size analyzer.

[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 ​​Smm 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 ​​Smm was punched out on the test samples of the separators. 2 The small disc is weighed and recorded as m3, and then the second bonding coating on the small disc is peeled off to obtain the mass of the small disc after peeling off the second bonding coating, recorded as m4, and the single-sided coating weight of the second bonding coating = (m3-m4) / S.

[0110] Test of thickness of first bonding coating and second bonding coating:

[0111] The coated separator is subjected to argon ion polishing or embedding sectioning to obtain a cross-section of the separator. The cross-section is observed using a scanning electron microscope (SEM) to measure the thickness of the first and second adhesive coating layers. In the cross-section of the separator, the side with the smaller particle diameter represents the first adhesive coating layer containing the first polymer binder, while the side with the larger particle diameter represents the second adhesive 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. The negative electrode sheet was cleaned with dimethyl carbonate and dried. 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 adhesion between the separator and the positive electrode sheet was measured using a 180° peel test. The lithium-ion batteries in the tested examples and comparative examples were discharged at 0.5C to 3V and then disassembled. The negative electrode sheet was peeled off. 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 54.2mm × 72.5mm samples. The separator and positive electrode sheet were then laminated and hot-pressed using a hot press at 85°C, 1MPa, and 85s. The laminated sample was then cut into 15mm × 54.2mm strips to obtain test strips for the adhesion test of the separator to the positive electrode sheet. A 15mm × 55mm 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 adhesion 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 a 180° peel test. The lithium-ion batteries in the tested examples and comparative examples were discharged at 0.5C to 3.0V and then disassembled. The positive electrode sheet was 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 strips 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] Cyclic dynamics performance test:

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

[0124] (1) Adjust the test temperature to a constant temperature of 25°C, place the temperature sensing line of the multi-channel thermometer at the center of the lithium-ion battery surface, and perform the following steps: 1) 10C constant current charge to 4.2V; 2) 8C constant current charge to 4.3V; 3) 6C constant current charge to 4.45V; 4) 4.45V constant voltage charge to 0.05C; 5) stand for 30 minutes; 6) 1C constant current discharge to 3.0V; 7) stand for 30 minutes; end;

[0125] Charging speed: the time from step 1) to step 4) in step (1);

[0126] Charging temperature rise: The difference between the maximum temperature of the lithium-ion battery surface temperature sensor line during the process of step (1) from step 1) to step 4) and the room temperature.

[0127] (2) Adjust the test temperature to 25°C and start the test: 1) 10C constant current charge to 4.2V; 2) 8C constant current charge to 4.3V; 3) 6C constant current charge to 4.45V; 4) 4.45V constant voltage charge 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 cycles (cls); end;

[0128] Capacity retention (%) = discharge capacity after 1000 cycles / first cycle discharge capacity × 100%.

[0129] The cycle kinetic performance is characterized by charging speed, charging temperature rise and capacity retention rate. Among them, the shorter the charging time and the smaller the charging temperature rise, the better the initial kinetic performance of the lithium-ion battery, and the higher the capacity retention rate, the better the cycle performance of the lithium-ion battery.

[0130] High temperature stability test:

[0131] Test the thickness of the lithium-ion battery after it is manufactured, referred to as the initial thickness of the lithium-ion battery;

[0132] 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;

[0133] After the lithium-ion battery is placed in a high and low temperature box at 85°C for 8 hours, the thickness of the lithium-ion battery after storage is tested, and the test is completed.

[0134] 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.

[0135] Example 1-1

[0136] <Preparation of Separator>

[0137] A single-layer polypropylene film with a thickness of 7 μm is used as the base material of the isolation membrane;

[0138] Ceramic particles of boehmite and ceramic coating binder butadiene-styrene polymer (butadiene and styrene mass ratio 1:1, weight average molecular weight Mw = 7×10 6 ), solvent deionized water is mixed in a mass ratio of 35:10:55. Specifically, 30 kg of butadiene-styrene polymer and deionized water are first added to a 60 L double planetary mixer and dispersed at 45° C. for 3 hours; then 16.1 kg of boehmite 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 zirconia beads with a diameter of 6 μm as the grinding medium to obtain a ceramic coating slurry; the average particle size of the boehmite ceramic particles is 2 μm;

[0139] The first polymer binder polyacrylic acid (Mw = 3 × 10 3 ), thickener sodium carboxymethyl cellulose (Mw = 80000) and wetting agent polyoxyethylene ether (Mw = 6 × 10 3 ) are mixed in a mass ratio of 91:0.5:8.5, deionized water is added as a solvent, and the mixture is 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 is 1.6 μm; the first polymer binder has a non-core-shell structure;

[0140] The second polymer binder polyvinylidene fluoride (Mw = 8 × 10 5 ) and auxiliary binder methacrylic acid according to a mass ratio of 90:10, deionized water is added as a solvent, and stirred evenly to form a second bonding coating slurry with a solid content of 75wt%; the average particle size of the second polymer binder is 25μm; the second polymer binder is a non-core-shell structure;

[0141] 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).

[0142] The single-sided coating weight of the first adhesive coating layer is Cw1 = 0.0006 mg / mm 2The 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 = 0.0023 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%.

[0143] <Preparation of positive electrode sheet>

[0144] The positive electrode active material is lithium cobalt oxide, the positive electrode conductive agent is single-walled carbon nanotubes, and the positive electrode binder is polyvinylidene fluoride (PVDF, Mw = 6×10 6 ) are mixed in a mass ratio of 95:3:2, N-methylpyrrolidone (NMP) is added as a solvent, and stirred under a vacuum mixer until a solid content of 75wt% and a uniform positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a 10μm thick positive electrode current collector aluminum foil 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 other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode active material layer. The sheet is then cold pressed, cut into pieces, and slit. After slit, it is dried at 85°C under vacuum for 4 hours to obtain a positive electrode sheet with a specification of 50mm×1300mm for use. Among them, the single layer thickness of the positive electrode active material layer is 38.5μm, and the thickness of the positive electrode sheet is 87μm. The tab area of ​​the positive electrode current collector is die-cut to form 18 positive tabs in one piece, and the compaction density of the positive electrode sheet is 4.0g / cm 3 The Dv99 of lithium cobalt oxide is 30 μm and the Dv50 is 13 μm.

[0145] <Preparation of negative electrode sheet>

[0146] The negative electrode active material and dispersant 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 97.5:1.0:1.5, 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 negative electrode slurry was obtained. The negative electrode slurry was evenly coated on 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 on one side with a negative electrode active material layer. The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode active material layer. The sheet was then cold pressed, cut, and slit, and then dried at 110°C under vacuum for 4 hours to obtain a negative electrode sheet measuring 56 mm x 1350 mm for future use. The thickness of the negative electrode active material layer was 58.5 μm, and the thickness of the negative electrode sheet was 123 μm. Eighteen negative electrode tabs were integrally formed in the tab area of ​​the negative electrode current collector by die-cutting, with a compact density of 1.5 g / cm2. The negative electrode active material has a Dv99 of 25 μm and a Dv50 of 9 μm. The types of negative electrode active materials are shown in Table 5.

[0147] <Preparation of Electrolyte>

[0148] Under an environment with a water content of less than 10 ppm, a lithium salt, an organic solvent, and an additive are prepared in a mass ratio of 9:90:1 to obtain an electrolyte. The lithium salt is lithium hexafluorophosphate, the additive is ethanedinitrile, and the organic solvents are n-propyl propionate, ethylene carbonate, and diethyl carbonate. The mass ratio of n-propyl propionate, ethylene carbonate, and diethyl carbonate is 40:30:30. Based on the mass of the electrolyte, the mass percentage of the chain carboxylic acid ester is W1 = 40% × 90% = 36%, the mass percentage of ethylene carbonate is W2 = 30% × 90% = 27%, and the mass percentage of diethyl carbonate is W3 = 30% × 90% = 27%.

[0149] <Preparation of lithium-ion batteries>

[0150] 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.

[0151] Example 1-2 to Example 1-22

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

[0153] When the mass percentage of the linear carboxylate changes, the mass percentages of ethylene carbonate and diethyl carbonate also change, while the mass ratio of the lithium salt, organic solvent, and additives remains unchanged. The sum of the mass percentages of the linear carboxylate, ethylene carbonate, and diethyl carbonate is W1+W2+W3=90%, with W2=W3. The sum of the mass percentages of the lithium salt, organic solvent, and additives is 100%.

[0154] Examples 1-23

[0155] Except that the mass ratio of lithium salt, organic solvent and additive was adjusted to 32:60:8 in <Preparation of Electrolyte>, the rest was the same as Example 1-1.

[0156] Examples 1-24

[0157] Except that the mass ratio of lithium salt, organic solvent and additive was adjusted to 16:80:4 in <Preparation of Electrolyte>, the rest was the same as Example 1-1.

[0158] Examples 1-25

[0159] Except that the mass ratio of lithium salt, organic solvent and additive was adjusted to 40:50:10 in <Preparation of Electrolyte>, the rest was the same as Example 1-1.

[0160] Examples 1-26

[0161] Except that the mass ratio of lithium salt, organic solvent and additive was adjusted to 4:95:1 in <Preparation of Electrolyte>, the rest was the same as Example 1-1.

[0162] Example 1-27 to Example 1-30

[0163] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0164] Examples 1-31

[0165] Except that in <Preparation of Lithium-ion Battery>, the first bonding coating layer in the separator is close to the positive electrode plate and the second bonding coating layer is close to the negative electrode plate, the rest is the same as Example 1-1.

[0166] Example 1-32 to Example 1-34

[0167] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0168] Example 2-1 to Example 2-12

[0169] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as Example 1-1.

[0170] Example 3-1

[0171] Except for adjusting the relevant preparation parameters according to Table 5, the rest is the same as Example 1-1.

[0172] Example 3-2 to Example 3-4

[0173] 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 5.

[0174] Example 3-5 and Example 3-6

[0175] Except for adjusting the relevant preparation parameters according to Table 5, the rest is the same as Example 1-1.

[0176] Comparative Examples 1 to 10

[0177] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0178] When the mass percentage of the linear carboxylate changes, the mass percentages of ethylene carbonate and diethyl carbonate also change, while the mass ratio of the lithium salt, organic solvent, and additives remains unchanged. The sum of the mass percentages of the linear carboxylate, ethylene carbonate, and diethyl carbonate is W1+W2+W3=90%, with W2=W3. The sum of the mass percentages of the lithium salt, organic solvent, and additives is 100%.

[0179] Comparative Example 11

[0180] <Preparation of Separator>

[0181] 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.

[0182] The rest is the same as Example 1-1.

[0183] <Preparation of lithium-ion batteries>

[0184] 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.

[0185] <Preparation of positive electrode sheet>, <Preparation of negative electrode sheet>, and <Preparation of electrolyte> are the same as those in Comparative Example 1.

[0186] Comparative Example 12

[0187] <Preparation of Separator>

[0188] 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.

[0189] The rest is the same as Example 1-1.

[0190] <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 11.

[0191] Comparative Example 13

[0192] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0193] When the mass percentage of the linear carboxylate changes, the mass percentages of ethylene carbonate and diethyl carbonate also change, while the mass ratio of the lithium salt, organic solvent, and additives remains unchanged. The sum of the mass percentages of the linear carboxylate, ethylene carbonate, and diethyl carbonate is W1+W2+W3=90%, with W2=W3. The sum of the mass percentages of the lithium salt, organic solvent, and additives is 100%.

[0194] Comparative Example 14

[0195] <Preparation of Separator> and <Preparation of Lithium Ion Battery> are the same as those in Comparative Example 11.

[0196] <Preparation of positive electrode sheet>, <Preparation of negative electrode sheet>, and <Preparation of electrolyte> are the same as those in Comparative Example 13.

[0197] Comparative Example 15

[0198] <Preparation of Separator> and <Preparation of Lithium Ion Battery> are the same as those in Comparative Example 12.

[0199] <Preparation of positive electrode sheet>, <Preparation of negative electrode sheet>, and <Preparation of electrolyte> are the same as those in Comparative Example 13. The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 5.

[0200] Table 1

[0201] Note: “\” in Table 1 indicates no corresponding parameter; the difference between Example 1-1 and Example 1-31 in Table 1 is:

[0202] 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 1-31, 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.

[0203] Table 2

[0204] From Examples 1-1 to 1-34 and Comparative Examples 1 to 15, it can be seen that the secondary battery of the embodiment of the present application, by respectively providing a first bonding coating and a second bonding coating on both sides of the separator, 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 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 content of the chain carboxylic acid ester in the electrolyte is within the scope of the present application, so that the separator has a high bonding force F1 to the positive electrode sheet and the separator has a high bonding force F2 to the negative electrode sheet, the secondary battery can simultaneously have a short charging time (i.e., a high charging speed), a low charging temperature rise, and a high capacity retention rate at a charging rate of 10C, and the secondary battery has a low expansion rate after being stored at 85°C for 8h. This shows that the secondary battery of the embodiment of the present application can take into account high temperature stability on the basis of having good cycle dynamics performance under super-fast charging conditions, that is, the secondary battery has better comprehensive performance under super-fast charging conditions. However, the content of chain carboxylic acid ester in the electrolyte of the secondary batteries of Comparative Examples 1 and 2 is not within the scope of the present application; the average particle size of the second polymer binder in the isolation membrane of the secondary batteries of Comparative Examples 3 and 4 is not within the scope of the present application; the average particle size of the first polymer binder in the isolation membrane of the secondary batteries of Comparative Examples 5 and 6 is not within the scope of the present application; the Dv99 of the negative electrode active material of the secondary batteries of Comparative Examples 7 and 8 is not within the scope of the present application; the Dv99 of the positive electrode active material of the secondary batteries of Comparative Examples 9 and 10 is not within the scope of the present application; the second battery of Comparative Example 11 has both sides of its isolation membrane set as the first bonding coating instead of the isolation membrane structure of the present application; the second battery of Comparative Example 12 has both sides of its isolation membrane set as the second bonding coating instead of the isolation membrane structure of the present application; Secondary batteries, whose Dv99 of positive electrode active materials and negative electrode active materials are not within the scope of this application, and the content of chain carboxylic acid esters in the electrolyte is not within the scope of this application; the secondary batteries of Comparative Examples 14 and 15, whose Dv99 of positive electrode active materials, Dv99 of negative electrode active materials, the content of chain carboxylic acid esters in the electrolyte and the isolation membrane are all not within the scope of this application; the secondary batteries of Comparative Examples 1 to 15 have a longer charging time (i.e., a lower charging speed) and / or a higher charging temperature rise and / or a lower capacity retention rate at a charging rate of 10C, or the thickness of the secondary batteries has a higher expansion rate after being stored at 85°C for 8h, indicating that the secondary batteries cannot take into account the charging time, charging temperature rise, capacity retention rate and expansion rate under super-fast charging conditions, that is, the secondary batteries cannot take into account both cycle dynamics and high temperature stability under super-fast charging conditions.

[0205] The Dv99 content of the positive electrode active material generally affects the cycle dynamics and high-temperature stability of the secondary battery. As can be seen from Examples 1-1 to 1-5, Comparative Examples 9 and 10, secondary batteries using Dv99 as the positive electrode active material, which falls within the scope of this application, exhibit a shorter charging time, lower charging temperature rise, and higher capacity retention at a 10C charge rate, and exhibit a lower thickness expansion rate after storage at 85°C for 8 hours. As a result, the secondary battery can achieve both good cycle dynamics and high-temperature stability under super-fast charging conditions.

[0206] The Dv99 negative electrode active material generally affects the cycle dynamics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 1-6, 1-9, Comparative Examples 7, and 8, secondary batteries using Dv99 negative electrode active materials within the scope of this application have a shorter charging time, lower charging temperature rise, and higher capacity retention at a 10C charge rate, and a lower thickness expansion rate after storage at 85°C for 8 hours. As a result, secondary batteries can achieve both good cycle dynamics and high-temperature stability under super-fast charging conditions.

[0207] The average particle size of the first polymer binder usually affects the cycle dynamics and high-temperature stability of the secondary battery. From Examples 1-1, 1-10 to 1-13, Comparative Examples 5 and 6, it can be seen that the secondary battery with an average particle size of the first polymer binder within the range of this application has a shorter charging time, a lower charging temperature rise, and a higher capacity retention rate at a charge rate of 10C, and a lower thickness expansion rate after storage at 85°C for 8 hours. As a result, the secondary battery can have good cycle dynamics under super-fast charging conditions while taking into account high-temperature stability.

[0208] The average particle size of the second polymer binder usually affects the cycle dynamics and high-temperature stability of the secondary battery. From Examples 1-1, 1-14 to 1-17, Comparative Examples 3 and 4, it can be seen that the secondary battery with an average particle size of the second polymer binder within the range of this application has a shorter charging time, a lower charging temperature rise, and a higher capacity retention rate at a charge rate of 10C, and a lower thickness expansion rate after storage at 85°C for 8 hours. As a result, the secondary battery can have good cycle dynamics under super-fast charging conditions while taking into account high-temperature stability.

[0209] The content of chain carboxylic acid ester in the electrolyte usually affects the cycle dynamics and high-temperature stability of the secondary battery. From Example 1-1, Example 1-18 to Example 1-26, Comparative Example 1 and Comparative Example 2, it can be seen that the secondary battery with the content of chain carboxylic acid ester in the electrolyte within the range of this application has a shorter charging time, lower charging temperature rise and higher capacity retention rate at a charging rate of 10C, and has a lower thickness expansion rate after storage at 85°C for 8h. As a result, the secondary battery can have good cycle dynamics performance under super-fast charging conditions while taking into account high-temperature stability.

[0210] The content of organic solvent in the electrolyte usually affects the cycle kinetics and high temperature stability of secondary batteries.

[0211] As shown in Examples 1-1, 1-23, and 1-26, secondary batteries containing an organic solvent content within the range of this application exhibit a shorter charging time, a lower charging temperature rise, and a higher capacity retention rate at a 10C charge rate. Furthermore, the thickness exhibits a lower expansion rate after storage at 85°C for 8 hours. This allows the secondary battery to maintain both good cycling dynamics and high-temperature stability under super-fast charging conditions.

[0212] The Dv50 of the positive electrode active material usually affects the cycle dynamics and high temperature stability of the secondary battery. It can be seen from Examples 1-1 to 1-5, 1-27 and 1-28 that the secondary battery using the positive electrode active material with a Dv50 within the scope of this application has a shorter charging time, a lower charging temperature rise and a higher capacity retention rate at a charging rate of 10C, and a lower thickness expansion rate after storage at 85°C for 8 hours. As a result, the secondary battery can have good cycle dynamics under super-fast charging conditions while taking into account high temperature stability. And, from

[0213] It can also be seen from Examples 1-2 and 1-27 that when the positive electrode active material with the same Dv99 has different Dv50, the cycle dynamics performance and high-temperature stability of the secondary battery will also be affected.

[0214] The Dv50 of the negative electrode active material usually affects the cycle dynamics and high temperature stability of the secondary battery. It can be seen from Example 1-1, Example 1-6 to Example 1-9, Example 1-29 and Example 1-30 that the secondary battery whose Dv50 of the negative electrode active material is within the scope of this application has a shorter charging time, a lower charging temperature rise and a higher capacity retention rate at a charging rate of 10C, and the thickness has a lower expansion rate after storage at 85°C for 8h. As a result, the secondary battery can have good cycle dynamics under super fast charging conditions while taking into account high temperature stability. Moreover, it can also be seen from Example 1-6, Example 1-9, Example 1-29 and Example 1-30 that when the negative electrode active material of the same Dv99 has different Dv50, the cycle dynamics and high temperature stability of the secondary battery will also be affected.

[0215] The positional relationship between the first and second adhesive coatings in the separator and the positive and negative electrode sheets usually affects the cycle dynamics and high-temperature stability of the secondary battery. As can be seen from Examples 1-1 and 1-31, the secondary battery selected in which the positional relationship between the first and second adhesive coatings in the separator and the positive and negative electrode sheets is within the scope of this application has a shorter charging time, a lower charging temperature rise, and a higher capacity retention rate at a charge rate of 10C, and a lower thickness expansion rate after storage at 85°C for 8 hours. As a result, the secondary battery can have good cycle dynamics under super-fast charging conditions while taking into account high-temperature stability.

[0216] The type of chain carboxylate generally affects the cycle dynamics and high-temperature stability of secondary batteries. As can be seen from Examples 1-1, 1-32, and 1-34, secondary batteries using chain carboxylate types within the scope of this application have a shorter charging time, lower charging temperature rise, and higher capacity retention at a charge rate of 10C, and a lower thickness expansion rate after storage at 85°C for 8 hours. As a result, secondary batteries can achieve both good cycle dynamics and high-temperature stability under super-fast charging conditions.

[0217] Table 3

[0218] Table 4

[0219] The coverage rate of the first polymer binder in the first adhesive coating per unit area, Cr1, the single-sided coating weight of the first adhesive coating, Cw1, and the thickness H1 of the first adhesive coating 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 the coverage rate of the first polymer binder in the first adhesive coating per unit area, Cr1, the single-sided coating weight of the first adhesive coating, Cw1, and the thickness H1 of the first adhesive coating within the scope of this application has a short charging time, a low charging temperature rise, and a high capacity retention rate at a charging rate of 10C, and a low expansion rate of the thickness after storage at 85°C for 8 hours. As a result, the secondary battery can have good cycle dynamics under super-fast charging conditions while taking into account high-temperature stability.

[0220] The coverage rate of the second polymer binder per unit area of ​​the second adhesive coating layer Cr2, the single-sided coating weight of the second adhesive coating layer Cw2, and the thickness of the second adhesive coating layer H2 generally affect the cyclic dynamics performance and high-temperature stability of the secondary battery. As can be seen from Examples 1-1, 2-5, and 2-8, the secondary battery selected for the coverage rate of the second polymer binder per unit area of ​​the second adhesive coating layer Cr2, the single-sided coating weight of the second adhesive coating layer Cw2, and the thickness of the second adhesive coating layer H2 within the scope of this application has a short charging time, a low charging temperature rise, and a high capacity retention rate at a charge rate of 10C, and a low expansion rate of the thickness after storage at 85°C for 8 hours. As a result, the secondary battery can have good cyclic dynamics performance under super-fast charging conditions while taking into account high-temperature stability.

[0221] The type of the first polymer binder generally affects the cycle dynamics and high-temperature stability of the secondary battery. As can be seen from Examples 1-1, 2-9, and 2-10, secondary batteries using the type of first polymer binder within the scope of this application have a shorter charging time, lower charging temperature rise, and higher capacity retention at a charge rate of 10C, and a lower thickness expansion rate after storage at 85°C for 8 hours. As a result, the secondary battery can achieve both good cycle dynamics and high-temperature stability under super-fast charging conditions.

[0222] The type of second polymer binder generally affects the cycle dynamics and high-temperature stability of the secondary battery. As can be seen from Examples 1-1, 2-11, and 2-12, the secondary battery using the type of second polymer binder within the scope of this application has a shorter charging time, lower charging temperature rise, and higher capacity retention at a charge rate of 10C, and has a lower thickness expansion rate after storage at 85°C for 8 hours. As a result, the secondary battery can have good cycle dynamics under super-fast charging conditions while taking into account high-temperature stability.

[0223] Table 5

[0224] Note: “\” in Table 5 indicates no corresponding parameter; “N1” in Table 5 indicates the mass ratio of artificial graphite to amorphous carbon.

[0225] Types of negative electrode active materials, carbon-based materials d / I g The value usually affects the cycle dynamics 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 scope of this application has a shorter charging time, a lower charging temperature rise and a higher capacity retention rate at a charging rate of 10C, and a lower thickness expansion rate after storage at 85°C for 8h. As a result, the secondary battery can have good cycle kinetics performance under super-fast charging conditions while taking into account high-temperature stability. 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 active material, its I d / I g A higher value indicates that it has good surface activity.

[0226] The type of positive electrode active material usually affects the cycle dynamics performance and high temperature stability of the secondary battery. It can be seen from Examples 1-1, 3-5 and 3-6 that the type of positive electrode active material, the carbon-based material d / I g Secondary batteries with values ​​within the range of this application have a short charging time, a low charging temperature rise, and a high capacity retention rate at a charging rate of 10C, and a low thickness expansion rate after storage at 85°C for 8 hours. As a result, the secondary batteries can achieve good cycle dynamics under super-fast charging conditions while also maintaining high-temperature stability.

[0227] 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.

[0228] 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.

[0229] 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: The invention comprises an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet comprises a positive electrode active material, the negative electrode sheet comprises a negative electrode active material, 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 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 comprises a second polymer binder, and the average particle size of the second polymer binder is 10 μm to 38 μm; The electrolyte includes an organic solvent, a lithium salt and an additive, wherein the organic solvent includes a chain carboxylic acid ester; Based on the mass of the electrolyte, the mass percentage of the chain carboxylic acid ester is 6% to 56%.

2. The secondary battery according to claim 1, wherein The Dv99 of the positive electrode active material is 28 μm to 31 μm, and / or the Dv99 of the negative electrode active material is 24 μm to 26 μm.

3. The secondary battery according to claim 1, wherein The average particle size of the first polymer binder is 0.6 μm to 1.6 μm; and / or the average particle size of the second polymer binder is 20 μm to 30 μm.

4. 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.

5. 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.

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 0.0001 mg / mm 2 To 0.001mg / mm 2 The single-sided coating weight of the second bonding coating is 0.0004 mg / mm 2 To 0.002mg / 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 is a core-shell structure, comprising a first shell and a first core, wherein the polymerizable monomer of the first shell comprises 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, and the polymerizable monomer of the first core comprises at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid or maleic acid; or, The first polymer binder is a non-core-shell structure, and the polymerized monomer of the 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 per unit area in the second bonding coating layer is 40% to 60%.

11. The secondary battery according to claim 1, wherein The second polymer binder is a core-shell structure, comprising a second outer shell and a second inner core, the polymerizable monomer of the second outer shell comprising at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, styrene, butadiene, acrylonitrile, acrylic acid, methyl acrylate or butyl acrylate, and the polymerizable monomer of the second inner core comprising at least one of ethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate or ethyl chloromethylacrylate; or, The second polymer binder is a non-core-shell structure, and the polymerization 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, styrene, butadiene or acrylonitrile.

12. The secondary battery according to claim 1, wherein The chain carboxylic acid ester includes at least one of methyl formate, methyl acetate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, methyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl butyrate, n-propyl butyrate, propyl isobutyrate, n-pentyl butyrate, n-pentyl isobutyrate, n-butyl butyrate, isobutyl isobutyrate or n-pentyl valerate.

13. The secondary battery according to claim 1, wherein Based on the mass of the electrolyte, the mass percentage of the chain carboxylic acid ester is 18% to 40%.

14. The secondary battery according to claim 1, wherein The organic solvent further comprises at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone or tetrahydrofuran; Based on the mass of the electrolyte, the mass percentage of the organic solvent is 60% to 90%.

15. The secondary battery according to claim 1, wherein The additive includes 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; Based on the mass of the electrolyte, the mass percentage of the additive is 2% to 20%.

16. 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 elemental silicon, silicon-carbon material or silicon-oxygen material, and the tin-based material includes at least one of elemental tin, tin alloy or tin oxide.

17. The secondary battery according to claim 16, wherein The carbon-based material is tested by Raman with a peak intensity ratio of d peak to g peak. d / I g Satisfy: 0.2≤I d / I g ≤1.

0.

18. 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.

19. The secondary battery according to claim 18, 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.

20. An electric device comprising the secondary battery according to any one of claims 1 to 19.

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