Secondary battery and electric device

Abstract

The present application provides a secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; the positive electrode sheet comprises a positive electrode active material layer, and the negative electrode sheet comprises a negative electrode active material layer; the coating weight of the positive electrode active material layer is Wz, the coating weight of the negative electrode active material layer is Wf, and Wz and Wf satisfy that: 1.6Wf≤Wz≤2.2Wf, and 3.25 mg / cm2≤Wf≤5.84 mg / cm2. The separator comprises 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 the two sides of the separator substrate. The electrolyte comprises a chain-like carboxylic acid ester, and based on the mass of the electrolyte, the mass percentage content of the chain-like carboxylic acid ester is 6% to 56%. The secondary battery provided by the present application has good cycle performance and high-temperature storage performance under fast charging conditions.

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, boast high specific energy, high operating voltage, low self-discharge, compact size, and light weight, making them widely used in various fields, including energy storage, portable electronic devices, and electric vehicles. With the continuous iterative development of consumer lithium-ion batteries in recent years, the market demand for their charging speeds has become increasingly stringent. The proportion of fast-charging products has gradually increased, and the charging rate has continued to rise. Consumer demand has gradually increased from 1C to 3C, 5C, 6C, 7C, and 10C. At a 10C rate, a lithium-ion battery can be fully charged in less than 15 minutes, providing users with a very good experience and providing great convenience in daily life.

[0003] However, to meet the requirements of fast charging and cycling, the high-temperature storage performance of lithium-ion batteries is affected. This is because side reactions in lithium-ion batteries increase under fast charging (charging rate ≥ 5C) and high temperature conditions (for example, temperatures greater than or equal to 40°C). Therefore, how to balance the cycling performance of lithium-ion batteries under fast charging conditions with the storage performance under high-temperature conditions has become a technical problem that needs to be solved by those skilled in the art.

[0004] Summary of the Invention

[0005] The purpose of the present application is to provide a secondary battery that takes into account both the cycle performance and high-temperature storage performance of the secondary battery, and at the same time provides an electrical device using the secondary battery.

[0006] 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:

[0007] The first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active material layer, and the negative electrode sheet comprises a negative electrode active material layer; the coating weight of the positive electrode active material layer is W z , the coating weight of the negative electrode active material layer is W f , W z and W f Between: 1.6W f ≤W z ≤2.2W f 、3.25mg / cm 2 ≤W f≤5.84mg / cm 2 The isolation film includes an isolation film substrate, a first bonding coating and a second bonding coating, the first bonding coating and the second bonding coating are respectively arranged on both sides of the isolation film substrate; the first bonding coating includes a first polymer binder, the average particle size of the first polymer binder is 0.3μm to 3μm; the second bonding coating includes a second polymer binder, 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, and the mass percentage of the chain carboxylic acid ester is 6% to 56% based on the mass of the electrolyte. The present application combines the coating weight of the positive electrode active material layer and the negative electrode active material layer, the isolation film and the electrolyte, and regulates W z 、W f , the mass percentage of the chain carboxylic acid ester, the average particle size of the first polymer binder and the average particle size of the second polymer binder are within the above ranges, which can enable the coating weight of the positive electrode active material layer and the negative electrode active material layer, the isolation membrane and the electrolyte to have a good synergistic effect, which is beneficial to accelerate the transmission of ions and the infiltration of the electrolyte, and can also improve the problem of gas production caused by the intensified interface side reactions between the electrolyte and the positive electrode plate or the negative electrode plate, so as to take into account the cycle performance and high-temperature storage performance of the secondary battery under fast charging conditions.

[0008] Fast-charging secondary batteries control the coating weight of the positive and negative active material layers within the above range, which can reduce the thickness of the active material layer, increase the porosity of the active material layer, reduce the transmission distance of the electrolyte in the electrode, accelerate the infiltration of the electrode, and improve the fast-charging performance. At the same time, by regulating the mass percentage of the chain carboxylic acid ester in the electrolyte within the above range, the lithium ion has 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 making the secondary battery have good cycle performance and fast-charging performance. 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 occur to produce a large amount of gas, resulting in poor high-temperature performance of the battery. The present application provides a first bonding coating and a second bonding coating on both sides of the isolation membrane, respectively, and the average particle size of the first polymer binder in the first bonding coating and the average particle size of the second polymer binder in the second bonding coating are within the above-mentioned range of the present application, which is beneficial to strengthening the interface between the isolation membrane and the electrode, inhibiting gas production under high temperature conditions, and improving the cycle performance and high-temperature storage performance. On one side of the second bonding coating of the isolation membrane, an electrolyte flow channel can be generated and the electrolyte can be stored, meeting the requirements of the secondary battery for high electrolyte retention (such as 1.5g / Ah to 2.4g / Ah) and high transmission and infiltration in the fast charging state, thereby improving the rate and cycle performance of the secondary battery.

[0009] In some embodiments of the present application, 6.49 mg / cm 2 ≤W z ≤11.69 mg / cm 2 By regulating W z When the value of is within the above range, the transmission distance of ions and electrons on the positive electrode sheet can be shortened, the infiltration speed of the electrolyte to the positive electrode sheet or the negative electrode sheet can be increased, which is beneficial to the transmission of ions, thereby improving the high-temperature storage performance of the secondary battery while further improving its cycle performance.

[0010] In some embodiments of the present application, the first bonding coating is disposed on the side of the separator substrate close to the negative electrode plate, and the second bonding coating is disposed on the side of the separator substrate close to the positive electrode plate. For most secondary batteries, fast charging is primarily 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 insertion of lithium ions into the negative electrode. Therefore, disposing the first bonding coating with smaller separator particles on the negative electrode plate can shorten the lithium ion transmission path during the charging process and achieve faster charging speeds.

[0011] In some embodiments 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, 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 electrolyte including the chain carboxylate has a low viscosity and a high electrical conductivity, is conducive to the transport of ions, and can further improve the cycle performance of the secondary battery on the basis of having good high-temperature storage performance.

[0012] In some embodiments of the present application, the organic solvent further comprises at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, or tetrahydrofuran; the weight percentage of the organic solvent is 70% to 80% based on the weight of the electrolyte. The inclusion of the above-mentioned organic solvents in the electrolyte can improve the stability of the electrolyte at high temperatures, thereby further improving the cycling performance and high-temperature storage performance of the secondary battery.

[0013] In some embodiments of the present application, the lithium salt includes 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; and the weight percentage of the lithium salt is 10% to 20% based on the weight of the electrolyte. The electrolyte includes the lithium salt within the above range and regulates its weight percentage within the above range. The lithium salt has a high solubility in the electrolyte, which can make the electrolyte have a high electrical conductivity, thereby improving the cycle performance of the secondary battery.

[0014] In some embodiments 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-tris(2-cyanoethoxy)propane; the weight percentage of the additive is 2% to 10% based on the weight of the electrolyte. By regulating the type and weight percentage of the additive within the above range, it is beneficial to improve the stability of the positive electrode and reduce the occurrence of side reactions in the electrolyte, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0015] In some embodiments 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 the above range, the electrolyte can have a lower viscosity and higher conductivity, which is conducive to ion transport, thereby further improving the cycle performance of the secondary battery while maintaining good high-temperature storage performance.

[0016] In some embodiments of the present application, 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. The bonding coating layer has a smaller particle size and stronger bonding force. Its thickness is 0.2 μm to 4 μm. It can maximize the energy density while maintaining high bonding force, while shortening the lithium ion transmission path in the active material layer corresponding to the first bonding coating layer. The second bonding coating layer has a larger particle size, which can form a channel for electrolyte circulation. It is set between 5 μm and 20 μm, which can improve the energy density of the secondary battery under the premise of good flow and wettability of the electrolyte.

[0017] In some embodiments 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 2By regulating the single-sided coating weight of the first bonding coating within the above range, the high bonding properties of the first bonding coating can be fully utilized, the electrode and the separator can be better bonded, and the mechanical reliability of the secondary battery can be ensured; by regulating the single-sided coating weight of the second bonding coating within the above range, the electrolyte flow channel between the electrode and the separator can be fully realized, and the dynamic and cycle performance of the secondary battery can be improved.

[0018] In some embodiments of the present application, the coverage of the first polymer binder per unit area of ​​the first bonding coating layer is 40% to 60%. By regulating the coverage of the first polymer binder per unit area of ​​the first bonding coating layer within the above range, the high bonding properties of the first bonding coating layer can be fully utilized. This facilitates the bonding of the separator and the electrode, allowing for faster lithium ion transmission speeds, enabling the secondary battery to achieve both cycling performance and high-temperature storage performance while having lower production costs.

[0019] In some embodiments of the present application, the first polymer binder includes a core-shell structure first polymer binder or a non-core-shell structure first polymer binder, the core of the core-shell structure first polymer binder includes at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid or maleic acid, the shell of the core-shell structure first polymer binder includes at least one of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, chloromethyl ethyl acrylate, chlorostyrene, fluorostyrene, methylstyrene, acrylonitrile or methacrylonitrile; the non-core-shell structure first polymer binder includes at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, fluorostyrene, chlorostyrene or propylene. The above-mentioned first polymer binder is applied to the first bonding coating layer, which can make the first bonding coating layer have high bonding force, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0020] In some embodiments of the present application, the coverage of the second polymer binder per unit area of ​​the second bonding coat layer is 40% to 60%. By regulating the coverage of the second polymer binder per unit area of ​​the second bonding coat layer within this range, the separator has a strong bond with the positive or negative electrode sheet, enabling the secondary battery to achieve both cycling performance and high-temperature storage performance while having a lower production cost.

[0021] In some embodiments of the present application, the polymerizable monomers of the second polymer binder include at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, allyl chloride, acrylic acid, acrylate, styrene, butadiene, acrylonitrile, methyl acrylate, butyl acrylate, ethyl acrylate, chlorostyrene, fluorostyrene, ethyl methacrylate, methyl methacrylate, butyl methacrylate, and ethyl chloromethylacrylate. The use of the aforementioned second polymer binder can provide a larger gap between the second bonding coating layer and the positive or negative electrode sheet, resulting in good bonding performance, better heat dissipation during cycling, and facilitated electrolyte transport, resulting in the secondary battery having good cycling performance and high-temperature storage performance under fast-charging conditions.

[0022] In some embodiments of the present application, the second polymer binder includes a core-shell structure second polymer binder or a non-core-shell structure second polymer binder; the polymerization monomer of the shell of the core-shell structure second polymer binder includes at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, styrene, butadiene, acrylonitrile, acrylic acid, methyl acrylate or butyl acrylate, and the core of the core-shell structure second polymer binder includes at least one of methyl acrylate, butyl acrylate, ethyl acrylate, ethyl methacrylate, methyl methacrylate, butyl methacrylate or ethyl chloromethyl acrylate; the polymerization monomer of the non-core-shell structure second polymer binder includes at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, propylene, chlorostyrene, fluorostyrene, vinylidene chloride, vinylidene fluoride, hexafluoropropylene, vinyl chloride or chloropropylene. The selection of the above-mentioned type of second polymer binder can provide a larger gap between the second bonding coating and the positive electrode sheet or the negative electrode sheet and have good bonding performance, and dissipate heat well during the cycle, so that the secondary battery has good cycle performance and high temperature storage performance under fast charging conditions.

[0023] The second aspect of the present application provides an electrical device comprising the secondary battery of any of the aforementioned embodiments. The secondary battery provided in the first aspect of the present application has good cycle performance and high-temperature storage performance. Therefore, the electrical device has good performance.

[0024] Beneficial effects of this application:

[0025] The present application provides a secondary battery and an electric device. In which, by combining the coating weight of the positive electrode active material layer and the negative electrode active material layer, the separator and the electrolyte, and regulating W z 、W fThe mass percentage of the chain carboxylic acid ester, the average particle size of the first polymer binder, and the average particle size of the second polymer binder within the scope of this application can achieve good synergy between the coating weight of the positive electrode active material layer and the negative electrode active material layer, the separator, and the electrolyte, which is beneficial for accelerating ion transmission and electrolyte infiltration, and can also improve the problem of gas production caused by the intensification of interfacial side reactions between the electrolyte and the positive electrode plate or the negative electrode plate, so as to take into account the cycle performance and high-temperature storage performance of the secondary battery under fast charging conditions. The electrical device of this application has good performance. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

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

[0032] Reference numerals: separator 30 , separator substrate 31 , first bonding coating 32 , second bonding coating 33 , ceramic coating 34 , positive electrode sheet 10 , negative electrode sheet 20 . DETAILED DESCRIPTION

[0033] 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.

[0034] 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.

[0035] The first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active material layer, and the negative electrode sheet comprises a negative electrode active material layer; the coating weight of the positive electrode active material layer is W z , the coating weight of the negative electrode active material layer is W f , W z and W f Between: 1.6W f ≤W z ≤2.2W f 、3.25mg / cm 2 ≤W f ≤5.84mg / cm 2 , such as W f Can be 3.25mg / cm 2 、3.5mg / cm 2 、3.75mg / cm 2 , 4mg / cm 2 , 4.25mg / cm 2 , 4.5mg / cm 2 , 4.75mg / cm 2 , 5mg / cm 2 , 5.25mg / cm 2 , 5.5mg / cm 2 , 5.84mg / cm 2 Or a range of any two values, W z Can be 1.6W f , 1.7W f , 1.8W f , 1.9W f , 2.0W f , 2.1W f , 2.2W fOr a range consisting of any two of the values. The isolation film comprises an isolation film substrate, a first bonding coating and a second bonding coating, and the first bonding coating and the second bonding coating are respectively arranged on both sides of the isolation 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, for example, the average particle size of the first polymer binder can be or is 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or a range consisting of any two of the values; 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, for example, the average particle size of the second polymer binder is 10 μm to 38 μm. The average particle size can be 10 μm, 15 μm, 25 μm, 26 μm, 30 μm, 35 μm, 38 μm or a range consisting of any two of the values; the electrolyte includes an organic solvent, a lithium salt and an additive, the organic solvent includes a chain carboxylate, and the mass percentage of the chain carboxylate is 6% to 56% based on the mass of the electrolyte, preferably 18% to 40%. For example, the mass percentage of the chain carboxylate can be 6%, 10%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 40%, 45%, 50%, 56% or a range consisting of any two of the values.

[0036] This application is regulated by W z and W f A value within the above range can shorten the transmission distance of ions (e.g., lithium ions) within the positive or negative electrode sheet, increase the rate of electrolyte penetration into the positive or negative electrode sheet, facilitate ion transmission, and thus improve the cycle performance of the secondary battery. A secondary battery comprising the above electrolyte and regulating the mass percentage of the linear carboxylate within the above range, with high conductivity and low viscosity, can increase the ion transmission rate and reduce the electrochemical polarization and concentration polarization of the secondary battery, thereby achieving good cycle performance. However, the high-dynamic system with the above characteristics will affect the high-temperature storage performance of the secondary battery. The secondary battery includes the above-mentioned isolation membrane, and regulates the average particle size of the first polymer binder and the average particle size of the second polymer binder within the above-mentioned range, which can enhance the bonding force between the isolation membrane and the positive electrode or the negative electrode, improve the problem of gas production caused by the intensified interface side reaction between the electrolyte and the positive electrode or the negative electrode, and improve the secondary high-temperature storage performance. At the same time, the isolation membrane with the above-mentioned characteristics can accelerate the transmission of ions and the infiltration of the electrolyte, thereby taking into account both the cycle performance and the high-temperature storage performance of the secondary battery.

[0037] The inventors found that when the coating weight of the positive electrode active material layer is less than 1.6W fThe coating weight of the negative electrode active material layer is too large relative to the coating weight of the positive electrode active material layer. When the potential of the secondary battery is reached, the delithiation rate of the positive electrode active material increases significantly, resulting in a very high actual potential of the positive electrode active material and easy destruction of the structure. The capacity of the positive electrode sheet decays rapidly, resulting in the secondary battery being unable to cycle normally. The coating weight of the positive electrode active material layer is greater than 2.2W f , the coating weight of the positive electrode active material layer is too large relative to the coating weight of the negative electrode active material layer, and the lithium ions released from the positive electrode are excessive. The negative electrode cannot accept all the lithium ions released from the positive electrode, and the lithium ions cannot be normally embedded in the negative electrode sheet, which will cause lithium deposition on the negative electrode sheet and affect the cycle dynamics performance of the secondary battery. f When it is too large, for example, greater than 5.84 mg / cm 2 , the transmission distance of ions in the positive electrode or negative electrode increases, the impedance of the secondary battery increases, which is not conducive to the transmission of lithium ions and cannot improve the cycle performance of the secondary battery. f Too small, for example, less than 3.25 mg / cm 2, the energy density of the secondary battery is reduced, the service life is reduced, and it is difficult to meet the application requirements of the secondary battery. When the average particle size of the first polymer binder is too small, for example, less than 0.3μm, the particles of the first polymer binder are prone to agglomeration when preparing the first bonding coating slurry. In this way, the probability of the first polymer binder being uniformly dispersed in the first bonding coating slurry is extremely small, and the distribution of the first polymer binder in the formed first bonding coating is uneven, which will affect the adhesion of the first bonding coating, and cannot improve the problem of gas production caused by the aggravated interface side reaction between the electrolyte and the positive electrode or the negative electrode, resulting in poor high-temperature storage performance of the secondary battery. When the average particle size of the first polymer binder is too large, for example, greater than 3μm, the gap between the particles of the first polymer binder will be too large, resulting in poor cycle performance. In addition, an excessively large average particle size of the first polymer binder will also increase the thickness of the first bonding coating, thereby increasing the volume of the secondary battery and causing its energy density to be lost. If the average particle size of the second polymer binder is too small, for example, less than 10 μm, the gap between the separator and the positive or negative electrode sheet is too small, and the electrolyte transmission channel is too narrow, which affects the electrolyte transmission and thus the cycling performance of the secondary battery. If the average particle size of the second polymer binder is too large, for example, greater than 38 μm, the thickness of the second bonding coat layer will increase, thereby increasing the volume of the secondary battery and resulting in a loss of energy density. Chain carboxylic acid esters have high conductivity, low viscosity, and facilitate lithium ion transport, giving the electrolyte high kinetic properties. If the weight percentage of chain carboxylic acid ester is too small, for example, less than 6%, the chain carboxylic acid ester content in the electrolyte is too low to fully utilize its inherent properties, which will affect the cycling performance of the secondary battery. If the weight percentage of chain carboxylic acid ester is too large, for example, greater than 56%, the chain carboxylic acid ester content in the electrolyte is too high, the electrolyte activity is too high, and side reactions in the electrolyte are particularly aggravated at high temperatures, leading to serious gassing problems in the secondary battery, thus affecting the high-temperature cycling performance of the secondary battery. Overall, the present application combines the coating weight of the positive electrode active material layer and the negative electrode active material layer, the isolation membrane and the electrolyte, and regulates the above parameters within the scope of the present application, so that there is a good synergistic effect between the coating weight of the positive electrode active material layer and the negative electrode active material layer, the isolation membrane and the electrolyte, so as to take into account the cycle performance and high-temperature storage performance of the secondary battery under fast charging conditions.

[0038] 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.

[0039] The secondary battery of the present application can be used under fast charging conditions, specifically, can be used at a charging rate of 5C to 15C. For example, the charging rate of the secondary battery is 5C, 8C, 10C, 12C, 15C or a range consisting of any two values ​​therein.

[0040] In this application, the average particle size can be understood as an equivalent diameter. This application does not particularly limit the method for regulating the average particle size of the first polymer binder, the average particle size of the second polymer binder, and the average particle size of the ceramic particles, as long as the purpose of this application can be achieved. For example, this can be achieved by purchasing a first polymer binder, a second polymer binder, and ceramic particles with an average particle size within the range of this application, or by adjusting the average particle size by crushing, grinding, or ball milling.

[0041] In some embodiments of the present application, 6.49 mg / cm 2 ≤W z ≤11.69mg / cm 2 , such as W z It can be 6.49mg / cm 2 、6.7mg / cm 2 , 7mg / cm 2 , 7.23mg / cm 2 , 7.5mg / cm 2 , 7.79mg / cm 2 , 8mg / cm 2 、8.24mg / cm 2 、8.5mg / cm 2 , 8.8mg / cm 2, 9mg / cm 2 , 9.2mg / cm 2 , 9.5mg / cm 2 , 9.7mg / cm 2 、10mg / cm 2 、10.2mg / cm 2 、10.5mg / cm 2 、10.7mg / cm 2 、11mg / cm 2 、11.69mg / cm 2 Or it can be a range consisting of any two values. By adjusting W z When the value of is within the above range, the transmission distance of ions and electrons on the positive electrode sheet can be shortened, the infiltration speed of the electrolyte to the positive electrode sheet or the negative electrode sheet can be increased, which is beneficial to the transmission of ions, thereby improving the high-temperature storage performance of the secondary battery while further improving its cycle performance.

[0042] In some embodiments of the present application, the first bonding coating is provided on the side of the separator substrate close to the negative electrode sheet, and the second bonding coating is provided on the side of the separator substrate close to the positive electrode sheet. As shown in FIG1 , the first bonding coating 32 is provided on the side of the separator substrate 31 close to the negative electrode sheet 20, and the second bonding coating 33 is provided on the side of the separator substrate 31 close to the positive electrode sheet 10. 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 a secondary battery mainly involves the embedding of lithium ions into the negative electrode. Therefore, the first bonding coating with smaller separator particles is provided on the negative electrode sheet side. This can shorten the lithium ion transmission path during the charging process and achieve faster charging speed. It is also beneficial for the positive electrode sheet or the negative electrode sheet to have excellent bonding properties with the separator, so that the secondary battery has good high-temperature storage performance.

[0043] In some embodiments 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, 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 electrolyte including the chain carboxylate has a low viscosity and a high electrical conductivity, is conducive to the transport of ions, and can further improve the cycle performance of the secondary battery on the basis of having good high-temperature storage performance.

[0044] In some embodiments 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; based on the mass of the electrolyte, the mass percentage of the organic solvent is 70% to 80%, for example, the mass percentage of the organic solvent can be 70%, 72%, 75%, 78%, 80%, or a range consisting of any two of these values. The electrolyte comprising the above-mentioned organic solvents can improve the stability of the electrolyte at high temperatures and can also have excellent kinetic properties, thereby further improving the cycle performance and high-temperature storage performance of the secondary battery.

[0045] Generally, the present application can regulate the mass percentage of the organic solvent by regulating the amount of organic solvent added to the electrolyte. The present application can regulate the mass percentage of the chain carboxylate by regulating the amount of the chain carboxylate added to the electrolyte. The mass percentage of the non-chain carboxylate in the organic solvent = the mass percentage of the organic solvent - the mass percentage of the chain carboxylate. In the present application, the non-chain carboxylate can be at least one of the above-mentioned ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone or tetrahydrofuran.

[0046] In some embodiments of the present application, the lithium salt includes 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; based on the mass of the electrolyte, the mass percentage of the lithium salt is 10% to 20%, for example, the mass percentage of the lithium salt can be 10%, 12%, 13%, 14%, 15%, 16%, 18%, 20%, or a range consisting of any two values ​​thereof. The electrolyte includes a lithium salt within the above range and regulates its mass percentage within the above range. The lithium salt has a higher solubility in the electrolyte, which can make the electrolyte have a higher conductivity, thereby improving the cycle performance of the secondary battery.

[0047] In some embodiments 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-tris(2-cyanoethoxy)propane; based on the mass of the electrolyte, the mass percentage of the additive is 2% to 10%, for example, the mass percentage of the additive can be 2%, 3%, 5%, 7%, 8%, 9%, 10% or a range consisting of any two values ​​therein. By regulating the type and mass percentage of the additive within the above range, a positive electrode solid electrolyte interface film (CEI film) can be formed on the surface of the positive electrode sheet, which is beneficial to improving the stability of the positive electrode sheet, reducing the dissolution of transition metals in the positive electrode active material, and also improving the stability of the negative electrode active material, reducing the occurrence of side reactions in the electrolyte, thereby improving the cycle performance and high temperature storage performance of the secondary battery under fast charging conditions.

[0048] 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 can be 0.2μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm or a range consisting of any two of the numerical values. 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 when its high bonding force is exerted, thereby improving the energy density of the fast-charging secondary battery and shortening the transmission path of lithium ions in the active material layer corresponding to the first bonding coating. Thus, the secondary battery can be made to have both cycle performance and high temperature storage performance while having high energy density.

[0049] In this application, the thickness of the first bonding coating layer and the thickness of the second bonding coating layer are obtained by observing and testing the parameters of the cross-sectional sample of the isolation membrane. This application does not particularly limit the method for preparing the cross-sectional sample of the isolation membrane, as long as it can achieve the purpose of this application. For example, the isolation membrane cross-sectional sample can be obtained by argon ion polishing or embedded sectioning.

[0050] 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 can be 5μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm or a range consisting of any two of the numerical values. The particle size of the second polymer binder in the second bonding coating is large, and a channel for electrolyte circulation can be formed. The thickness of the second bonding coating is regulated within the above range. The second bonding coating has a suitable thickness and can reduce the risk of energy density loss caused by the increase in the volume of the secondary battery due to the excessive thickness when the electrolyte has good flow wettability in the pole piece and the separator. In this way, the secondary battery can take into account both cycle performance and high temperature storage performance while having high energy density.

[0051] 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 can be 0.0001 mg / mm 2 , 0.0004mg / mm 2 、 0.0005mg / mm 2 , 0.0007mg / mm 2 , 0.0009mg / mm 2 , 0.001mg / mm 2 or a range consisting of any two of these values. By regulating the single-sided coating weight of the first bonding coating within the above range, the first bonding coating can better bond the positive electrode sheet or negative electrode sheet and the separator while exerting its high bonding effect. 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 achieve both cycling performance and high-temperature storage performance while having high energy density.

[0052] 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 may be 0.0004 mg / mm 2 , 0.0008mg / mm 2 , 0.001mg / mm 2 , 0.0012mg / mm 2 , 0.00015mg / mm 2 , 0.0018mg / mm 2 , 0.002mg / mm 2or a range consisting of any two of these values. By regulating the single-sided coating weight of the first bonding coating within the above range, the electrolyte flow channel between the positive electrode sheet or the negative electrode sheet and the separator can be fully realized, thereby improving the dynamic performance and cycle performance 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 achieve both cycle performance and high-temperature storage performance while having high energy density.

[0053] In some embodiments of the present application, the coverage rate Cr1 of the first polymer binder in the first bonding coating per unit area is 40% to 60%, for example, Cr1 can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, or a range consisting of any two values ​​therein. By regulating the coverage rate of the first polymer binder in the first bonding coating per unit area within the above range, the first polymer binder can play a role of high bonding force, and can give full play to the high bonding properties of the first bonding coating, which is beneficial to the bonding of the separator and the electrode, and is beneficial to the transmission of lithium ions, so that the secondary battery has both cycle performance and high temperature storage performance, while having good dynamic performance.

[0054] In some embodiments of the present application, the first polymer binder includes a core-shell structure first polymer binder or a non-core-shell structure first polymer binder, the core of the core-shell structure first polymer binder includes at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid or maleic acid, the shell of the core-shell structure first polymer binder includes at least one of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, chloromethyl ethyl acrylate, chlorostyrene, fluorostyrene, methylstyrene, acrylonitrile or methacrylonitrile; the non-core-shell structure first polymer binder includes at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, fluorostyrene, chlorostyrene or propylene. The above-mentioned first polymer binder is applied to the first bonding coating layer, which can make the first bonding coating layer have higher bonding force, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0055] In the present application, the isolation membrane may further include 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 includes 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 includes 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 Figure 5, the isolation membrane 30 includes an isolation membrane 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 arranged on both sides of the isolation membrane substrate 31, and a layer of ceramic coating 34 is arranged between the isolation membrane substrate 31 and the first bonding coating 32. At the same time, another layer of ceramic coating 34 is arranged between the isolation membrane substrate 31 and the second bonding coating 33.

[0056] It should be noted that the two ceramic coating layers mentioned above can be the same or different. Ceramic coatings have excellent hardness and heat resistance. Providing a ceramic coating on the separator can improve the hardness and heat resistance of the secondary battery, thereby enabling the secondary battery to have good thermal safety and mechanical reliability in addition to good kinetic and cycling performance. This application does not specifically limit the thickness of the ceramic coating; for example, the thickness of the ceramic coating can be 0.5 μm to 6 μm. The ceramic coating comprises ceramic particles and a ceramic coating binder. This application does not specifically limit the type of ceramic coating binder, as long as it can achieve the objectives of this application. For example, ceramic coating binders include but are not limited to at least one of polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, polybutyl acrylate, or polyacrylonitrile. This application does not specifically limit the content of ceramic particles and ceramic coating binder in the ceramic coating, as long as it can achieve the objectives of this application. For example, the weight percentage of ceramic particles is 5% to 95%, and the weight percentage of ceramic coating binder is 5% to 95%, based on the mass of the ceramic coating. This application does not specifically limit the separator substrate, as long as it can achieve the objectives of this application. For example, the structure of the separator 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 separator substrate includes at least one of polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET). The separator substrate can have a thickness of 3 μm to 20 μm.

[0057] In the present application, the first bonding coating layer includes a first polymer binder and may also include 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 coating 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 can be 85% to 95%, the mass percentage of the thickener can be 0.5% to 2%, the mass percentage of the auxiliary binder can be 0% to 15%, and the mass percentage of the wetting agent can be 4% to 10%. The present application does not particularly limit the types of the above-mentioned thickeners, auxiliary binders, and wetting agents, as long as they can achieve the purpose of this application. For example, thickeners include but are not limited to sodium carboxymethyl cellulose. 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 they can achieve the purpose of this application. For example, monovinyl compounds include but are not limited to at least one of styrene, chlorostyrene, fluorostyrene, or methylstyrene. Wetting agents may include but are not limited to sodium carboxymethyl cellulose, dimethyl siloxane, polyethylene oxide dimethyl siloxane, polyethylene oxide, oxyethylene alkylphenol ethers, polyoxyethylene fatty alcohol ethers, oxyethylene alkylphenol ethers, polyoxyethylene fatty alcohol ethers, polyoxyethylene polyoxypropylene block copolymers, dioctyl sodium sulfosuccinate, etc.

[0058] In some embodiments of the present application, the coverage rate Cr2 of the second polymer binder in the second bonding coating per unit area is 40% to 60%. For example, Cr2 can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60% or a range consisting of any two of these values. The coverage rate of the second polymer binder in the second bonding coating per unit area is regulated within the above range. When the second polymer binder provides a large gap between the second bonding coating and the positive electrode sheet or between the second bonding coating and the negative electrode sheet, a wider electrolyte transmission channel can be provided during the cycle. The electrolyte has good flow wettability in the positive electrode sheet, the negative electrode sheet and the separator, so that the second bonding coating has a suitable thickness, thereby reducing the risk of energy density loss caused by the increase in the volume of the fast-charging secondary battery due to the excessive thickness, thereby enabling the secondary battery to have a higher energy density while taking into account both cycle performance and high temperature storage performance.

[0059] In some embodiments of the present application, 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, acrylate, styrene, butadiene, acrylonitrile, methyl acrylate, butyl acrylate, ethyl acrylate, chlorostyrene, fluorostyrene, ethyl methacrylate, methyl methacrylate, butyl methacrylate, and ethyl chloromethylacrylate. The use of the above-mentioned second polymer binder can provide a larger gap between the second bonding coating and the positive or negative electrode sheet and have good bonding properties. The electrolyte has good flow and wettability in the positive electrode sheet, negative electrode sheet, and separator, which is beneficial for the transmission of the electrolyte, resulting in the secondary battery having good cycle performance and high-temperature storage performance under fast charging conditions.

[0060] In some embodiments of the present application, the second polymer binder includes a core-shell structure second polymer binder or a non-core-shell structure second polymer binder; the polymerization monomer of the shell of the core-shell structure second polymer binder includes at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, styrene, butadiene, acrylonitrile, acrylic acid, methyl acrylate or butyl acrylate, and the core of the core-shell structure second polymer binder includes at least one of methyl acrylate, butyl acrylate, ethyl acrylate, ethyl methacrylate, methyl methacrylate, butyl methacrylate or ethyl chloromethylacrylate; the polymerization monomer of the non-core-shell structure second polymer binder includes at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, propylene, chlorostyrene, fluorostyrene, vinylidene chloride, vinylidene fluoride, hexafluoropropylene, vinyl chloride or propylene chloride. The selection of the above-mentioned type of second polymer binder can create a larger gap between the second bonding coating and the positive electrode sheet or the negative electrode sheet and have good bonding properties, and the electrolyte has good flow and wettability in the positive electrode sheet, the negative electrode sheet and the isolation membrane, which is beneficial to the transmission of the electrolyte, so that the secondary battery has good cycle performance and high-temperature storage performance under fast charging conditions.

[0061] In the present application, the second bonding coating layer includes a second polymer binder and may further include an auxiliary binder. The auxiliary binder is applied to the second bonding coating layer, and can bond the second polymer binder to the isolation membrane substrate and / or ceramic coating during the application of the second bonding coating layer slurry. The present application does not particularly limit the type of auxiliary binder, as long as the purpose of the present application can be achieved. For example, it can be the same as the auxiliary binder in the above-mentioned first bonding coating layer. The present application does not particularly limit the content of the second polymer binder and the auxiliary binder in the second bonding coating layer, as long as the purpose of the present application can be achieved. For example, based on the mass of the second bonding coating layer, the mass percentage of the second polymer binder is 85% to 95%, and the mass percentage of the auxiliary binder is 5% to 15%.

[0062] The positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. In some embodiments, the positive electrode active material layer is disposed on one surface of the positive electrode current collector. In other embodiments, the positive electrode active material layer is disposed on both surfaces of the positive electrode current collector, wherein the above-mentioned "surface" can be part of the surface or the entire surface of the positive electrode current collector. The present application has no particular restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The positive electrode active material layer of the present application includes a positive electrode active material. The present application has no particular restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material can include at least one of lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. In the present application, the positive electrode active material may also contain non-metallic elements, for example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm, preferably 6μm to 18μm. The thickness of the single-sided positive electrode material layer is 30μm to 120μm. In the present application, the positive electrode active material layer may also include a positive electrode conductor and a positive electrode binder. In the present application, there is no particular restriction on the type of positive electrode binder in the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application does not particularly limit the type of positive electrode conductive agent in the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.The present application does not particularly limit the mass ratio of the cathode active material, the cathode conductive agent, and the cathode binder in the cathode active material layer. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved. For example, the mass ratio of the cathode active material, the cathode conductive agent, and the cathode binder in the cathode active material layer is (95 to 98):(0.5 to 2.5):(1.5 to 3.4).

[0063] The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. In some embodiments, the negative electrode active material layer is provided on one surface of the negative electrode current collector. In other embodiments, the negative electrode active material layer is provided on both surfaces of the negative electrode current collector. Herein, the above "surface" can be a partial surface or the entire surface of the negative electrode current collector. The present application does not particularly limit the negative electrode current collector as long as the purpose of the present application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.). The negative electrode active material layer of the present application contains a negative electrode active material. The present application does not particularly limit the type of the negative electrode active material as long as the purpose of the present application can be achieved. For example, the negative electrode active material can include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12, Li-Al alloy or metallic lithium. In the present application, there is no particular restriction on the thickness of the negative electrode current collector and the negative electrode 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 4μm to 20μm, and the thickness of the negative electrode active material layer is 30μm to 130μm. Optionally, the negative electrode active material layer may also include a negative electrode conductive agent and a negative electrode binder. The present application has no particular restriction on the type of conductive agent in the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the negative electrode conductive agent may be the same as the type of positive electrode conductive agent in the above-mentioned positive electrode active material layer. The present application has no particular restriction on the type of negative electrode binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the negative electrode binder may be the same as the type of positive electrode binder in the above-mentioned positive electrode active material layer. Optionally, the negative electrode active material layer may also include a stabilizer. The present application has no particular restriction on the type of stabilizer. For example, the stabilizer may include sodium carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the mass ratio of the negative electrode active material, the negative electrode conductive agent, the stabilizer, and the negative electrode binder in the negative electrode active material layer can be (96 to 98): (0.5 to 2): (0 to 1.5): (1.0 to 1.9).

[0064] 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.

[0065] 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.

[0066] The present application does not impose any particular restrictions on the method for preparing the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the positive electrode sheet includes but is not limited to the following steps: (1) preparing a positive electrode slurry; (2) coating the positive electrode slurry on one surface of the positive electrode main region of the positive electrode current collector, and after drying, forming a positive electrode active material layer on one surface of the positive electrode main region of the positive electrode current collector; (3) coating the positive electrode slurry on the other surface of the positive electrode main region of the positive electrode current collector, and after drying, forming a positive electrode active material layer on each of the two surfaces of the positive electrode main region of the positive electrode current collector; (4) cold pressing, cutting, and slitting to obtain the positive electrode sheet. The present application does not impose any particular restrictions on the solid content of the positive electrode slurry in the above step (1), as long as the coating weight of the obtained positive electrode active material layer is within the range of the present application and the purpose of the present application can be achieved. For example, the solid content of the positive electrode slurry is 70wt% to 80wt%. The present application does not impose any particular restrictions on the drying time and temperature in the above steps (2) and (3), as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the process parameters of the cold pressing in the above step (4), as long as the purpose of the present application can be achieved.

[0067] The present application does not impose any particular restrictions on the method for preparing the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the negative electrode sheet includes but is not limited to the following steps: (1) preparing a negative electrode slurry; (2) coating the negative electrode slurry on one surface of the negative electrode main region of the negative electrode current collector, and after drying, forming a negative electrode active material layer on one surface of the negative electrode main region of the negative electrode current collector; (3) coating the negative electrode slurry on the other surface of the negative electrode main region of the negative electrode current collector, and after drying, forming a negative electrode active material layer on each of the two surfaces of the negative electrode main region of the negative electrode current collector; (4) cold pressing, cutting, and slitting to obtain the negative electrode sheet. The present application does not impose any particular restrictions on the solid content of the negative electrode slurry in the above step (1), as long as the coating weight of the obtained negative electrode active material layer is within the range of the present application and the purpose of the present application can be achieved. For example, the solid content of the negative electrode slurry is 40wt% to 60wt%. The present application does not impose any particular restrictions on the drying time and temperature in the above steps (2) and (3), as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the process parameters of the cold pressing in the above step (4), as long as the purpose of the present application can be achieved.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] The second aspect of the present application provides an electrical device comprising the secondary battery of any of the aforementioned embodiments. The secondary battery provided in the first aspect of the present application has good cycle performance and high-temperature storage performance. Therefore, the electrical device has good performance.

[0076] 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.

[0077] Example

[0078] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0079] Test methods and equipment:

[0080] The coating weight W of the positive electrode active material layer z test:

[0081] The lithium-ion batteries of each embodiment and comparative example were discharged at 0.5C to 3.0V, and then disassembled to obtain the positive electrode sheets. The positive electrode sheets were soaked in dimethyl carbonate (DMC) solution for 4 hours, dried, and cut into pieces with an area of ​​A mm 2 The positive electrode sheet sample is placed on a balance and weighed, which is recorded as p1. Then the positive electrode active material layer on the positive electrode sheet is scraped off and cleaned to obtain the positive electrode current collector. The positive electrode current collector is placed on a balance and weighed, which is recorded as p2. If the positive electrode sheet is coated with a positive electrode active material layer on one side, W z =(p1-p2) / A. If it is a positive electrode sheet with a positive electrode active material layer coated on both sides, W z =(p1-p2) / 2A.

[0082] The coating weight W of the negative electrode active material layer f test:

[0083] After the lithium-ion batteries of each embodiment and comparative example were discharged to 3.0V at 0.5C, the negative electrode sheets were disassembled and soaked in DMC solution for 4 hours, dried, and cut into pieces with an area of ​​B mm.2 The negative electrode sheet sample is placed on a balance and weighed, which is recorded as q1. Then the negative active material layer on the negative electrode sheet is scraped off and cleaned to obtain the positive electrode current collector. The negative electrode current collector is placed on a balance and weighed, which is recorded as q2. If the negative electrode sheet is coated with a negative active material layer on one side, W f =(q1-q2) / B. If it is a negative electrode sheet with a negative electrode active material layer coated on both sides, W f =(q1-q2) / 2B.

[0084] Average particle size test:

[0085] For the average particle size of the first polymer binder and the second polymer binder, the surface of the isolation membrane perpendicular to the thickness direction can be observed by a scanning electron microscope (SEM), and the diameters of 10 first polymer binders and 10 second polymer binder particles are measured respectively, and the average value is obtained. Wherein, the first polymer binder and the second polymer binder are distinguished by the size of the particle diameter. Specifically, in the surface of the isolation membrane, the side with a relatively smaller diameter of each particle is the first bonding coating containing the first polymer binder, and 10 first polymer binders are arbitrarily selected in the first bonding coating to obtain the average particle size of the first polymer binder; the side with a relatively larger diameter of each particle is the second bonding coating containing the second polymer binder, and 10 second polymer binders are arbitrarily selected in the second bonding coating to obtain the average particle size of the second polymer binder. Since the particles of the first polymer binder and the second polymer binder will be deformed under the pressure of cold pressing, hot pressing and other processes during the preparation of the secondary battery, the diameters of the particles along the thickness direction of the isolation membrane and the direction perpendicular to the thickness direction of the isolation membrane are different. The average particle size of the first polymer binder and the second polymer binder of the present application is the diameter measured on the surface of the particles perpendicular to the thickness direction of the isolation membrane. Therefore, the average particle size of the above-mentioned first polymer binder and the second polymer binder is not limited by the thickness of the first bonding coating and the second bonding coating.

[0086] Test of single-sided coating weight of the first bonding coat:

[0087] The lithium-ion batteries of the examples and comparative examples were discharged at 0.5C to 3.0V, and then disassembled to obtain the separators. The impurities on the separator surface were cleaned with DMC and dried at 60°C to obtain the test samples of the separators. An area of ​​S mm was punched out on the test samples of the separators. 2 The small disc is weighed and recorded as m1, and then the first bonding coating on the small disc is peeled off to obtain the mass of the small disc after peeling off the first bonding coating, which is recorded as m2. The single-sided coating weight of the first bonding coating = (m1-m2) / S.

[0088] Test for single-sided coating weight of the second bonding coat:

[0089] The lithium-ion batteries of the examples and comparative examples were discharged at 0.5C to 3.0V, and then disassembled to obtain the separators. The impurities on the separator surface were cleaned with DMC and dried at 60°C to obtain the test samples of the separators. An area of ​​S mm was punched out on the test samples of the separators. 2 The small disc is weighed and recorded as m3, and then the second 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.

[0090] Tests of the thickness of the first bonding coating and the thickness of the second bonding coating:

[0091] The coated separator was subjected to argon ion polishing to obtain a cross-section of the separator. The cross-section was observed using a scanning electron microscope to measure the thickness of the first bonding coating layer and the thickness of the second bonding coating layer. In the cross-section of the separator, the side with the smaller particle diameter represents the first bonding coating layer containing the first polymer binder, while the side with the larger particle diameter represents the second bonding coating layer containing the second polymer binder.

[0092] Test of coverage of the first polymer binder:

[0093] The surface of the isolation membrane provided with the first adhesive coating was observed using a scanning electron microscope (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.

[0094] Second polymer binder coverage test:

[0095] 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 substance in the electron microscope photograph by the area of ​​the isolation membrane sampled in the entire electron microscope photograph.

[0096] Test of the bonding force F1 of the separator to the positive electrode:

[0097] 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 3.0V 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 composited and hot-pressed using a hot press at 85°C, 1MPa, and 85s. The composited sample was 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.

[0098] Test of the bonding force F2 of the separator to the negative electrode:

[0099] The adhesion 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 between the separator and the negative electrode sheet, F2, was then measured in N / m, following the same procedure as described for the separator-to-positive-electrode adhesion test.

[0100] Cycle performance test:

[0101] The cycle performance of lithium-ion batteries is evaluated by capacity retention. The higher the capacity retention, the better the cycle performance. The charging process of the lithium-ion batteries of each embodiment and comparative example is divided into three stages for step charging. The charging rate is 10C / 8C / 6C to perform cycle performance test. The specific test steps are as follows: adjust the test temperature to 25℃ constant temperature and start the test: (1) 10C constant current charging to 4.2V; (2) 8C constant current charging to 4.3V; (3) 6C constant current charging to 4.45V; (4) 4.45V constant voltage charging to 0.05C; (5) stand for 5min; (6) 1C constant current discharge to 3.0V; (7) stand for 5min; 8) steps (1) to (7) are cycled for 1000 cycles (cls); end, record the first cycle discharge capacity and the discharge capacity after 1000cls of the lithium-ion battery. Capacity retention (%) = discharge capacity after 1000 cycles / first cycle discharge capacity × 100%.

[0102] High temperature storage performance test:

[0103] The high-temperature storage performance of lithium-ion batteries is evaluated by the expansion rate of lithium-ion batteries. The smaller the expansion rate, the better the high-temperature storage performance. The thickness of the lithium-ion battery in the state of lithium-ion battery preparation is tested, referred to as the initial thickness of the lithium-ion battery. The lithium-ion battery is fully charged according to the following steps: charging to 4.45V at a constant current of 0.7C, and charging to 0.02C at a constant voltage of 4.45V; then testing the thickness of the lithium-ion battery in the fully charged state. After the lithium-ion battery is placed in an 80°C environment and stored for 8 hours, the thickness of the lithium-ion battery after storage is tested, and the test is completed. 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%.

[0104] Example 1-1

[0105] <Preparation of Separator>

[0106] The ceramic particles aluminum oxide, ceramic coating binder butadiene-styrene polymer (butadiene and styrene mass ratio is 2:1, weight average molecular weight Mw=8×10 6 ), solvent deionized water are 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 aluminum oxide ceramic particles are added to the mixer and dispersed at high speed at 45 ° C for 2 hours; then ball milling is carried out using a nano grinder for 1.5 hours. The grinding medium used is spherical zirconium oxide beads with a diameter of 6 μm to obtain a ceramic coating slurry; the average particle size of the ceramic particles is 2 μm.

[0107] The first polymer binder polyacrylic acid (Mw = 6000), the thickener sodium carboxymethyl cellulose and the wetting agent polyoxyethylene ether (Mw = 8000) are mixed in a mass ratio of 91:2:7, 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 is a non-core-shell structure.

[0108] The second polymer binder polyvinylidene fluoride (Mw = 850000) and the auxiliary binder methacrylic acid are mixed in a mass ratio of 93:7, 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.

[0109] A single-layer polypropylene film with a thickness of 5 μm was used as the separator substrate. A ceramic coating slurry was applied to one surface of the separator substrate and dried at 60°C to form a ceramic coating on the one surface of the separator substrate. A second bonding coating slurry was applied to the surface of the ceramic coating facing away from the separator substrate and dried at 60°C to form a second bonding coating on the surface of the ceramic coating facing away from the separator substrate. A first bonding coating slurry was applied to the other surface of the separator substrate and dried at 60°C to form a first bonding coating on the other surface of the separator substrate. This produced a separator (see, but not limited to, Figure 4 for the structure).

[0110] The single-sided coating weight of the first adhesive coating layer is Cw1 = 0.0006 mg / mm 2 The thickness of the first bonding coating layer is H1 = 2 μm, and the single-sided coating weight of the second bonding coating layer is Cw2 = 0.0012 mg / mm 2 The thickness of the second bonding coating is H2 = 12 μm. The single-sided coating weight of the ceramic coating is Cw3 = 0.06 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%.

[0111] <Preparation of positive electrode sheet>

[0112] The positive electrode active material is lithium cobalt oxide, the positive electrode conductive agent is carbon fiber, and the positive electrode binder is polyvinylidene fluoride (PVDF, Mw = 7×10 6) are mixed in a mass ratio of 95:2.5:2.5, N-methylpyrrolidone (NMP) is added as a solvent, and stirred under the action of a vacuum mixer to a positive electrode slurry with a solid content of 75wt% and a uniform system. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, 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. After cold pressing, cutting, and slitting, after slitting, it is dried at 85°C under vacuum conditions for 4h to obtain a positive electrode sheet with a specification of 60mm×1580mm for standby 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 90μm. The tab area of ​​the positive electrode current collector is formed into 18 positive tabs by die-cutting. The coating weight W of the positive electrode active material layer z 9.08 mg / cm 2 .

[0113] <Preparation of negative electrode sheet>

[0114] The negative electrode active material artificial graphite, negative electrode conductive agent Super P, stabilizer sodium carboxymethyl cellulose (CMC-Na, Mw = 7 × 10 5 ), negative electrode binder styrene-butadiene rubber (SBR, Mw = 6 × 10 6 ) are mixed in a mass ratio of 96.5:1.0:1.0:1.5, and then deionized water is added as a solvent, and stirred under the action of a vacuum mixer until the solid content is 51wt% and the system is uniform. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 10μm, and dried at 85°C to obtain a negative electrode sheet with a single-sided negative electrode active material layer. Thereafter, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode active material layer. Then, it is cold pressed, cut into pieces, and slit, and after slit, it is dried at 110°C under vacuum conditions for 4h to obtain a negative electrode sheet with a specification of 62mm×1600mm for standby use. Among them, the single layer thickness of the negative electrode active material layer is 58.5μm, and the thickness of the negative electrode sheet is 127μm. The tab area of ​​the negative electrode current collector is formed into 18 negative electrode tabs by die-cutting. The coating weight W of the negative electrode active material layer f 4.54 mg / cm 2 .

[0115] <Preparation of Electrolyte>

[0116] In an environment with a water content of less than 10 ppm, a linear carboxylate n-propyl propionate, a non-linear carboxylate ethylene carbonate, and diethyl carbonate are mixed to obtain an organic solvent. A lithium salt of lithium hexafluorophosphate (LiPF6) and an additive, succinonitrile, are then added, dissolved, and mixed uniformly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of the linear carboxylate n-propyl propionate is 30%, the mass percentage of the lithium salt LiPF6 is 15%, the mass percentage of the additive is 7%, and the balance is the non-linear carboxylate ethylene carbonate and diethyl carbonate, with the mass ratio of the two being 1:1.

[0117] <Preparation of lithium-ion batteries>

[0118] 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.

[0119] Example 1-2 to Example 1-16

[0120] The process is the same as Example 1-1 except that the relevant parameters are adjusted according to Table 1. When the mass percentage of the chain carboxylate changes, the mass percentage of the non-chain carboxylate changes accordingly, while the mass percentages of the lithium salt and additives remain unchanged.

[0121] Examples 1-17

[0122] Except for the following process of <Preparation of Lithium Ion Battery>, the rest is the same as Example 1-1.

[0123] <Preparation of lithium-ion batteries>

[0124] 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 positive electrode sheet, while the second adhesive coating layer is adjacent to the negative electrode sheet. The electrode assembly is then wound together. The electrode assembly is then 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.

[0125] Example 2-1 to Example 2-6

[0126] The process was the same as Example 1-1 except that the mass percentages of the organic solvent, lithium salt and additives were adjusted according to Table 2, the mass percentage of the chain carboxylate remained unchanged, and the mass percentage of the non-chain carboxylate was changed accordingly.

[0127] Example 2-7 to Example 2-9

[0128] Except for adjusting the type of the chain carboxylic acid ester according to Table 2, the rest is the same as Example 1-1.

[0129] Example 2-10 to Example 2-11

[0130] Except for adjusting the type of non-chain carboxylic acid ester according to Table 2, the rest is the same as Example 1-1.

[0131] Example 2-12

[0132] Except for adjusting the type of lithium salt according to Table 2, the rest is the same as Example 1-1.

[0133] Example 2-13

[0134] Except for adjusting the types of additives according to Table 2, the rest is the same as Example 1-1.

[0135] Example 3-1 to Example 3-12

[0136] Except for adjusting the relevant parameters according to Table 3, the rest is the same as Example 1-1.

[0137] Comparative Example 1

[0138] In addition to preparing the isolation film according to the following <Preparation of Isolation Film> process, and adjusting W according to Table 1 f 、W z , no chain carboxylate is added to the electrolyte, the mass percentage of non-chain carboxylate changes accordingly, and the mass percentage of lithium salt and additives remain unchanged, and the rest is the same as Example 1-1.

[0139] <Preparation of Separator>

[0140] A single-layer polypropylene film with a thickness of 5 μm was used as the isolation film substrate. Aluminum oxide ceramic particles, ceramic coating binder butadiene-styrene polymer (butadiene and styrene mass ratio 2:1, weight average molecular weight Mw = 8×10 6), solvent deionized water is mixed in a mass ratio of 35:10:55. Specifically: first, 30 kg of butadiene-styrene polymer and deionized water are added to a double planetary mixer with a volume of 60 L, and dispersed at 45°C for 3 hours; then 16.1 kg of aluminum oxide ceramic particles are added to the mixer and dispersed at high speed at 45°C for 2 hours; then, ball milling is performed using a nano grinder for 1.5 hours. The grinding medium used is spherical zirconium oxide beads with a diameter of 6 μm to obtain a ceramic coating slurry; the average particle size of the ceramic particles is 2 μm; the ceramic coating slurry is applied 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 to obtain an isolation membrane.

[0141] Comparative Example 2 to Comparative Example 11

[0142] In addition to adjusting W according to Table 1 f 、W z , the average particle size of the first polymer binder, the average particle size of the second polymer binder, and the mass percentage of the chain carboxylic acid ester in the electrolyte, the mass percentage of the non-chain carboxylic acid ester changes accordingly, and the mass percentage of the lithium salt and the additive remains unchanged, and the rest is the same as Example 1-1.

[0143] Comparative Example 12

[0144] Except for the following processes of <Preparation of Separator> and <Preparation of Lithium-ion Battery>, the rest is the same as Example 1-1.

[0145] <Preparation of Separator>

[0146] The ceramic coating slurry, the preparation method for applying the first bonding coating slurry, and the isolation membrane substrate were the same as those in Example 1-1. The ceramic coating slurry was applied to one surface of the isolation membrane substrate and dried at 60°C to form a ceramic coating on the one surface of the isolation membrane substrate. The first bonding coating slurry was applied to the surface of the ceramic coating away from the isolation membrane substrate and dried at 60°C to form a first bonding coating on the surface of the ceramic coating away from the isolation membrane substrate. The first bonding coating slurry was applied to the other surface of the isolation membrane substrate and dried at 60°C to form a first bonding coating on the other surface of the isolation membrane substrate, thereby producing an isolation membrane.

[0147] <Preparation of lithium-ion batteries>

[0148] 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.

[0149] Comparative Example 13

[0150] Except for the following process of <Preparation of Isolation Film>, the rest is the same as Comparative Example 12.

[0151] <Preparation of Separator>

[0152] 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.

[0153] Comparative Example 14

[0154] In addition to adjusting W according to Table 1 f 、W z , the mass percentage of the chain carboxylate, the mass percentage of the non-chain carboxylate changes accordingly, and the mass percentage of the lithium salt and the additive remains unchanged, and the rest is the same as Comparative Example 12.

[0155] Comparative Example 15

[0156] In addition to adjusting W according to Table 1 f 、W z , the mass percentage of the chain carboxylate, the mass percentage of the non-chain carboxylate changes accordingly, and the mass percentage of the lithium salt and the additive remains unchanged, and the rest is the same as Comparative Example 13.

[0157] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0158] Table 1 Note: “ / ” in Table 1 indicates no relevant parameters.

[0159] From Example 1-1 to Example 1-14 and Comparative Example 1 to Comparative Example 8, it can be seen that the present invention can achieve the desired effect by adjusting W f and W z The value of is within the scope of this application, and the first bonding coating and the 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 scope of this application, and a chain carboxylate is added to the electrolyte, and the mass percentage of the chain carboxylate is regulated within the scope of this application, so that the isolation membrane has a greater bonding force to the positive electrode sheet or the negative electrode sheet, and the lithium-ion battery has a higher capacity retention rate under fast charging conditions, and a lower expansion rate after storage at 80°C for 8 hours, indicating that the lithium-ion battery of this application has better cycle performance and high-temperature storage performance under fast charging conditions. In contrast, the lithium-ion battery of Comparative Example 1, W f and Wz The value of is not within the scope of this application, the first bonding coating or the second bonding coating is not provided on both sides of the separator, and no chain carboxylate is added to the electrolyte; the lithium ion batteries in Comparative Examples 2 to 3, W f It is not within the scope of this application. The lithium ion batteries in Comparative Examples 4 and 5, W z Not within the scope of the present application, the average particle size of the first polymer binder in the separator of the lithium ion batteries of Comparative Examples 6 and 7 is not within the scope of the present application; the average particle size of the second polymer binder in the separator of the lithium ion batteries of Comparative Examples 8 and 9 is not within the scope of the present application; the mass percentage of the chain carboxylic acid ester in the lithium ion batteries of Comparative Examples 10 and 11 is not within the scope of the present application, the lithium ion battery of Comparative Example 12 has both sides of its separator set as the first bonding coating, rather than the separator structure of the present application; the lithium ion battery of Comparative Example 13 has both sides of its separator set as the second bonding coating, rather than the separator structure of the present application; the lithium ion battery of Comparative Example 14 has both sides of its separator set as the first bonding coating, and W f and W z The value of and the mass percentage of the chain carboxylic acid ester are not within the scope of this application. In the lithium-ion battery of Comparative Example 15, both sides of the separator are provided with a second bonding coating, rather than the separator structure of this application; and W f and W z The value of and the mass percentage of the chain carboxylic acid ester are not within the scope of this application. In the lithium-ion batteries of Comparative Examples 1 to 15, the capacity retention rate of the lithium-ion batteries under fast charging conditions is lower and / or the expansion rate is higher after storage at 80°C for 8 hours, indicating that the cycle performance and / or high-temperature storage performance of the lithium-ion batteries under fast charging conditions are worse.

[0160] W f The value of W usually affects the cycle performance and high temperature storage performance of lithium ion batteries. From Example 1-1 to Example 1-3 and Comparative Example 2 to Comparative Example 3, it can be seen that W f The lithium-ion battery with a value within the scope of this application has a high capacity retention rate under fast charging conditions and a low expansion rate after storage at 80°C for 8 hours, indicating that the lithium-ion battery has good cycle performance and high-temperature storage performance under fast charging conditions. The coating weight W of the positive electrode active material layer of Comparative Example 2 is z The coating weight W of the negative electrode active material layer f Although the capacity retention rate of the obtained lithium-ion battery is high and the expansion rate is small, the coating weight of the positive electrode active material layer and the negative electrode active material layer is too low, and the cost of accurately controlling the coating weight in actual industrial production is too high. The qualified rate of the lithium-ion battery obtained in large-scale production is too low and the energy density of the obtained lithium-ion battery is too low, which cannot meet the needs of actual production and is not suitable for industrial production applications.

[0161] W z / W f The value of W usually affects the cycle performance and high temperature storage performance of lithium ion batteries. From Example 1-1, Example 1-4 to Example 1-5, Comparative Example 4 to Comparative Example 5, it can be seen that W z / W f The lithium-ion battery with a value within the scope of this application has a higher capacity retention rate under fast charging conditions, and a lower expansion rate after storage at 80°C for 8 hours, indicating that the lithium-ion battery has better cycle performance and high-temperature storage performance under fast charging conditions.

[0162] W z The value of W usually affects the cycle performance and high temperature storage performance of lithium ion batteries. z The lithium-ion battery with a value within the scope of this application has a high capacity retention rate under fast charging conditions, and a low expansion rate after storage at 80°C for 8 hours, indicating that the lithium-ion battery has good cycle performance and high-temperature storage performance under fast charging conditions.

[0163] The average particle size of the first polymer binder typically affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-8, 1-9, and Comparative Examples 6 and 7, lithium-ion batteries with an average particle size of the first polymer binder within the range of this application exhibit greater adhesion of the separator to the negative electrode sheet, higher capacity retention under fast-charging conditions, and lower expansion after storage at 80°C for 8 hours, indicating that the lithium-ion batteries have better cycling performance and high-temperature storage performance under fast-charging conditions.

[0164] The average particle size of the second polymer binder typically affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-10, 1-11, and Comparative Examples 8 and 9, lithium-ion batteries with an average particle size of the first polymer binder within the range of this application have a greater adhesion of the separator to the positive electrode sheet, a higher capacity retention rate under fast charging conditions, and a lower expansion rate after storage at 80°C for 8 hours, indicating that the lithium-ion battery has better cycling performance and high-temperature storage performance under fast charging conditions.

[0165] The positional relationship between the first and second adhesive coatings in the separator and the positive and negative electrode sheets generally affects the kinetic performance, cycling performance, and mechanical reliability of a secondary battery. As can be seen from Examples 1-1 and 1-17, the poor adhesion between the second polymer binder, polyvinylidene fluoride, and the negative electrode sheet results in a low bonding force F2 between the separator and the negative electrode sheet. This results in the lithium-ion battery of Example 1-17 being more susceptible to swelling and having relatively poor cycling performance compared to the lithium-ion battery of Example 1-1.

[0166] The mass percentage of chain carboxylate esters typically affects the cycling performance and high-temperature storage performance of lithium-ion batteries. The lithium-ion batteries in Examples 1-1, 1-12, 1-16, and Comparative Examples 10 and 11, in which the mass percentage of chain carboxylate esters is outside the scope of this application, show that lithium-ion batteries with a mass percentage of chain carboxylate esters within the scope of this application exhibit higher capacity retention under fast-charging conditions and lower expansion rates after storage at 80°C for 8 hours, indicating that lithium-ion batteries have better cycling performance and high-temperature storage performance under fast-charging conditions.

[0167] Table 2 Note: “ / ” in Table 2 indicates no relevant parameters or substances. The mass ratio of the two solvents of non-chain carboxylic acid esters in Table 2 is 1:1.

[0168] The mass percentages of organic solvents, lithium salts, and additives generally affect the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1, and 2-6, lithium-ion batteries with mass percentages of organic solvents, lithium salts, and additives in the electrolyte within the ranges of this application exhibit high capacity retention under fast-charge conditions and low expansion rates after storage at 80°C for 8 hours, indicating that the lithium-ion batteries exhibit good cycling performance and high-temperature storage performance under fast-charge conditions.

[0169] The type of chain carboxylate generally affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-7, and 2-9, lithium-ion batteries using chain carboxylate types within the scope of this application exhibit high capacity retention under fast-charging conditions and low expansion after storage at 80°C for 8 hours, demonstrating good cycling performance and high-temperature storage performance under fast-charging conditions.

[0170] The type of non-chain carboxylate generally affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-10, and 2-11, lithium-ion batteries using non-chain carboxylate within the scope of this application exhibit high capacity retention under fast-charging conditions and low expansion after storage at 80°C for 8 hours, demonstrating good cycling performance and high-temperature storage performance under fast-charging conditions.

[0171] The type of lithium salt generally affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1 and 2-12, lithium-ion batteries using lithium salts within the scope of this application exhibit high capacity retention under fast-charging conditions and low expansion after storage at 80°C for 8 hours, demonstrating good cycling performance and high-temperature storage performance under fast-charging conditions.

[0172] The type of additive generally affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1 and 2-13, lithium-ion batteries using additives within the scope of this application exhibit high capacity retention under fast-charge conditions and low expansion after storage at 80°C for 8 hours, demonstrating good cycling performance and high-temperature storage performance under fast-charge conditions.

[0173] Table 3

[0174] The coverage rate of the first polymer binder per unit area in the first bonding coating layer, Cr1, the single-sided coating weight of the first bonding coating layer, Cw1, and the thickness H1 of the first bonding coating layer generally affect the cycling performance and high-temperature storage performance of the lithium-ion battery. As can be seen from Examples 1-1, 3-1, and 3-4, the lithium-ion battery with the values ​​of Cr1, Cw1, and H1 within the scope of this application has a large adhesion force between the separator and the positive or negative electrode sheet, a high capacity retention rate under fast charging conditions, and a low expansion rate after storage at 80°C for 8 hours, indicating that the lithium-ion battery has good cycling performance and high-temperature storage performance under fast charging conditions.

[0175] The coverage rate Cr2 of the second polymer binder per unit area of ​​the second bonding coat, the single-sided coating weight Cw2 of the second bonding coat, and the thickness H2 of the second bonding coat generally affect the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-5, and 3-8, lithium-ion batteries with values ​​of Cr2, Cw2, and H2 within the scope of this application have a strong bonding force between the separator and the positive or negative electrode sheet, a high capacity retention rate under fast charging conditions, and a low expansion rate after storage at 80°C for 8 hours, indicating that the lithium-ion battery has good cycling performance and high-temperature storage performance under fast charging conditions.

[0176] The type of first polymer binder generally affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-9, and 3-10, lithium-ion batteries using a first polymer binder within the scope of this application exhibit strong adhesion of their separators to the positive or negative electrode sheets, high capacity retention under fast-charging conditions, and low expansion after storage at 80°C for 8 hours, demonstrating good cycling performance and high-temperature storage performance under fast-charging conditions.

[0177] The type of second polymer binder generally affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-11, and 3-12, lithium-ion batteries using a second polymer binder within the scope of this application exhibit strong adhesion between the separator and the positive or negative electrode, high capacity retention under fast-charging conditions, and low expansion after storage at 80°C for 8 hours, demonstrating good cycling performance and high-temperature storage performance under fast-charging conditions.

[0178] 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, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0179] 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.

[0180] 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 comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active material layer, the negative electrode sheet comprises a negative electrode active material layer; the coating weight of the positive electrode active material layer is W z The coating weight of the negative electrode active material layer is W f , W z and W f Between: 1.6W f ≤W z ≤2.2W f , 3.25mg / cm 2 ≤W f ≤5.84mg / cm 2 ; The 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. The organic solvent includes a chain carboxylate. Based on the mass of the electrolyte, the mass percentage of the chain carboxylate is 6% to 56%.

2. The secondary battery according to claim 1, wherein 6.49mg / cm 2 ≤W z ≤11.69mg / cm 2 。 3. 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.

4. 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, 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.

5. 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 70% to 80%.

6. The secondary battery according to claim 1, wherein The lithium salt includes 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; based on the mass of the electrolyte, the mass percentage of the lithium salt is 10% to 20%.

7. 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-tris(2-cyanoethoxy)propane; based on the mass of the electrolyte, the mass percentage of the additive is 2% to 10%.

8. 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%.

9. 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.

10. 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 .

11. 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%.

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

13. 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%.

14. The secondary battery according to claim 1, wherein 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, ethyl acrylate, chlorostyrene, fluorostyrene, ethyl methacrylate, methyl methacrylate, butyl methacrylate, ethyl chloromethylacrylate, styrene, butadiene or acrylonitrile.

15. The secondary battery according to claim 1, wherein The second polymer binder includes a core-shell structure second polymer binder or a non-core-shell structure second polymer binder; The polymerized monomer of the shell of the core-shell structure second polymer binder includes at least one of vinylidene chloride, vinylidene fluoride, hexafluoropropylene, styrene, butadiene, acrylonitrile, acrylic acid, methyl acrylate or butyl acrylate, and the core of the core-shell structure second polymer binder includes at least one of methyl acrylate, butyl acrylate, ethyl acrylate, ethyl methacrylate, methyl methacrylate, butyl methacrylate or ethyl chloromethylacrylate; The polymerizable monomer of the non-core-shell structured second polymer binder includes at least one of acrylic acid, methyl acrylate, butyl acrylate, butadiene, styrene, acrylonitrile, ethylene, propylene, chlorostyrene, fluorostyrene, vinylidene chloride, vinylidene fluoride, hexafluoropropylene, vinyl chloride or allyl chloride. 16 . An electric device comprising the secondary battery according to claim 1 .

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