Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises an electrolyte and an isolating membrane, the electrolyte comprises a lithium salt additive and ethylene glycol bis (propionitrile) ether, based on the total mass of the electrolyte, the mass percentage content of the lithium salt additive is A%, the mass percentage content of the ethylene glycol bis (propionitrile) ether is B%, 0.035 < = A / B < = 20, and 0.005 < = B < = 2.9; the lithium salt additive meets at least one of the following characteristics: a, the lithium salt additive comprises lithium bis (fluorosulfonyl) imide, wherein A is more than or equal to 0.1 and less than or equal to 2.5; b, the lithium salt additive comprises lithium tetrafluoroborate, and 0.1 < = A < = 2.5; the isolating membrane comprises a base material layer, the porosity of the base material layer is P%, and P is larger than or equal to 15 and smaller than or equal to 35. The electrolyte and the isolating membrane are adopted, and the A / B value, the A value, the B value and the P value are regulated in the application range, so that the secondary battery has relatively good low-temperature floating charge performance, safety performance and overcharge resistance under high temperature and high pressure.

Description

[0001] This application is a divisional application of the application with the application number 202510029396.0, the application date of January 8, 2025, and the invention title of "A secondary battery and an electronic device". Technical Field

[0002] This application relates to the field of electrochemistry technology, and particularly to a secondary battery and an electronic device. Background Art

[0003] Secondary batteries, such as lithium-ion batteries, are widely used in fields such as smart phones, wearable devices, consumer drones, and electric vehicles due to their advantages such as high energy density, long cycle life, and no memory effect. With the wide application of lithium-ion batteries in the above fields, the market has higher and higher performance requirements for lithium-ion batteries. However, there are many side reactions between the positive electrode plate and the electrolyte, and between the negative electrode plate and the electrolyte during the cycling of existing lithium-ion batteries, which will affect the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device to improve the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of the secondary battery. The specific technical solutions are as follows:

[0005] In the first aspect of this application, a secondary battery is provided. The secondary battery includes an electrolyte and a separator. The electrolyte includes a lithium salt additive and ethylene glycol bis(propionitrile) ether. Based on the total mass of the electrolyte, the mass percentage content of the lithium salt additive is A%, and the mass percentage content of ethylene glycol bis(propionitrile) ether is B%, where 0.035 ≤ A / B ≤ 20. The lithium salt additive satisfies at least one of the following characteristics: a. The lithium salt additive includes lithium bis(fluorosulfonyl)imide, and 0.1 ≤ A ≤ 2.5; b. The lithium salt additive includes lithium tetrafluoroborate, and 0.1 ≤ A ≤ 2.5. The separator includes a substrate layer, and the porosity of the substrate layer is P%, where 15 ≤ P ≤ 35. In this application, an electrolyte including a lithium salt additive and ethylene glycol bis(propionitrile) ether is used. The chelating effect of ethylene glycol bis(propionitrile) ether can adsorb the ions after the solvation of the lithium salt additive, and a cathode solid electrolyte interface film (CEI film) can be formed at the interface between the positive electrode plate and the electrolyte. By regulating the values of A / B and A within the scope of this application, the CEI film can have good mechanical strength and chemical stability, and good compactness and uniformity, which can inhibit the formation of electrolyte side reactions and reduce the generation of interface gas. At the same time, by regulating the porosity of the separator substrate layer within the scope of this application, the CEI film and the separator at the interface can have compatible ion permeability and electronic insulation, so that the secondary battery of this application has good low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure.

[0006] In some embodiments, 0.047 ≤ A / B ≤ 10. By regulating the value of A / B within the above range, the mechanical strength and chemical stability of the CEI film formed by the lithium salt additive and ethylene glycol bis(propionitrile) ether can be further improved, making the ion permeability and electron insulation of the CEI film more compatible, thereby further improving the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0007] In some embodiments, 0.047 ≤ A / B ≤ 5. By regulating the value of A / B within the above range, the mechanical strength and chemical stability of the CEI film formed by the lithium salt additive and ethylene glycol bis(propionitrile) ether can be further improved, making the ion permeability and electron insulation of the CEI film more compatible, thereby further improving the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0008] In some embodiments, 15 ≤ P ≤ 25. By regulating the value of P within the above range, the CEI film and the separator can simultaneously have better electron insulation and ion permeability, and the separator itself meets certain structural strength and stability. At the same time, by using the electrolyte in the present application, the risk of separator deformation can be reduced, which is beneficial to improving the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0009] In some embodiments, the electrolyte further includes 4,4'-diphenylether dicarboxylic acid. Based on the total mass of the electrolyte, the mass percentage content of 4,4'-diphenylether dicarboxylic acid is C%, and 0.5 ≤ C ≤ 2.5. By using an electrolyte that further includes 4,4'-diphenylether dicarboxylic acid and regulating the value of C within the above range, 4,4'-diphenylether dicarboxylic acid can form a more stable, more uniform, and thinner CEI film with the lithium salt additive and ethylene glycol bis(propionitrile) ether. At the same time, it can form a stable and thin solid electrolyte interface film (SEI film) at the interface between the negative electrode plate and the electrolyte, and enable the formed SEI film and CEI film to both have good electron insulation and ion permeability, thereby facilitating the improvement of the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0010] In some embodiments, the electrolyte further includes methylene methanedisulfonate. Based on the total mass of the electrolyte, the mass percentage content of methylene methanedisulfonate is D%, and 0.01 ≤ D ≤ 0.5. By using an electrolyte that further includes methylene methanedisulfonate and regulating the value of D within the above range, methylene methanedisulfonate can form a more stable, more uniform, and thinner CEI film with the lithium salt additive and ethylene glycol bis(propionitrile) ether, and enable the formed SEI film to have good electron insulation and ion permeability, thereby facilitating the improvement of the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0011] In some embodiments, the separator membrane further includes a first coating on at least one surface of the substrate layer. The first coating includes an adhesive layer, and the average wall thickness between adjacent pores in the adhesive layer is T nm, where 2 ≤ T ≤ 450. When the average wall thickness between adjacent pores in the adhesive layer is within the scope of this application, the adhesion uniformity between the separator membrane and the electrode sheet can be improved, the risk of the electrode sheet detaching caused by a large difference in the bonding strength in a local area can be reduced, and thus the phenomenon of lithium deposition and black spots in some areas caused by the difference in the local rate of lithium ion transmission can be reduced. As a result, while the secondary battery of this application has good low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, it also has good low-temperature rate performance and safety performance. At the same time, when the average wall thickness between adjacent pores in the adhesive layer is within the above range, the strength of the separator membrane is relatively uniform, which can enable the secondary battery to have a higher passing rate in safety tests and thus have better safety performance.

[0012] In some embodiments, the separator membrane further includes a second coating on at least one surface of the substrate layer. On the surface of the second coating, in a region of 2 μm × 2 μm, the ratio of the apparent concentration of nitrogen element to the apparent concentration of carbon element is Y, where 1 ≤ Y ≤ 8. When the ratio Y of the apparent concentration of nitrogen element to the apparent concentration of carbon element on the surface of the second coating of the separator membrane is within the scope of this application, there are nitrogen-containing functional groups in the separator membrane, which can play a stable binding role with the metal ions of the positive electrode active material, reduce the binding energy, make the structure of the separator membrane and the positive electrode sheet more stable, enable the secondary battery to have a higher passing rate in safety tests, and at the same time can reduce the gas generation amount and self-discharge during the cycling of the secondary battery, and reduce the voltage drop. As a result, while the secondary battery of this application has good low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, it also has good low-temperature discharge performance and safety performance.

[0013] In some embodiments, 1 ≤ Y ≤ 4. By adjusting the ratio Y of the apparent concentration of nitrogen element to the apparent concentration of carbon element within the above range, the nitrogen-containing functional groups in the separator membrane can better play a more stable binding role with the metal ions on the positive electrode active material, further reduce the binding energy, thereby making the structure of the separator membrane and the positive electrode sheet more stable, enabling the secondary battery to have a higher passing rate in safety tests, and at the same time can further reduce the gas generation amount and self-discharge during the cycling of the secondary battery, and reduce the voltage drop. As a result, while the secondary battery of this application has good low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, it also has better low-temperature discharge performance and safety performance.

[0014] In some embodiments, the secondary battery further includes a positive electrode plate, which includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector. The dyne value of the positive electrode current collector is E dyn / cm, the positive electrode active material layer includes a positive electrode active material, the average particle size of the positive electrode active material is F μm, and 0.5 ≤ E / F ≤ 30. In the present application, the ratio E / F of the dyne value of the positive electrode current collector to the average particle size of the positive electrode active material is within the scope of the present application, and the surface tension of the positive electrode current collector itself is adapted to the positive electrode active material particles used, so that the force between the two is appropriate, which can make the positive electrode plate have a higher strength and maintain good structural stability when using the electrolyte of the present application. It can make the secondary battery have a higher passing rate in the safety test, and at the same time can reduce the gas generation amount during the cycling of the secondary battery and reduce the voltage drop, so that the secondary battery has good low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, while also having good low-temperature discharge performance and safety performance.

[0015] In some embodiments, 1 ≤ E / F ≤ 12.5. When the ratio E / F of the dyne value of the positive electrode current collector to the average particle size of the positive electrode active material is within the above range, the positive electrode plate can have a higher strength and maintain better structural stability when using the electrolyte of the present application, so that the secondary battery has good low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, while also having better low-temperature discharge performance and safety performance.

[0016] In some embodiments, the specific surface area of the positive electrode active material is S m 2 / g, and 0.05 ≤ S ≤ 0.86. The positive electrode active material with a specific surface area within the above range has an active specific surface area and structural strength adapted to the above electrolyte, which is beneficial to improving the structural stability of the positive electrode plate. It can make the secondary battery have a higher passing rate in the safety test, and at the same time can reduce the voltage drop of the secondary battery and improve the low-temperature rate performance of the secondary battery, so that the secondary battery has good low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, while also having good low-temperature discharge performance, low-temperature rate performance and safety performance.

[0017] In some embodiments, the positive electrode active material contains aluminum element. The positive electrode active material contains aluminum element, and the aluminum element participates in the formation of the interfacial CEI film, which can improve the Young's modulus of the interfacial CEI film, improve the strength and hardness of the CEI film, reduce the influence of the generated gas on the CEI film, and reduce the risk of CEI film decomposition. It can improve the self-discharge of the secondary battery and reduce the voltage drop, so that the secondary battery has good low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, while also having good low-temperature discharge performance, low-temperature rate performance and safety performance.

[0018] In some embodiments, 1 ≤ F ≤ 30. The positive electrode active material with an average particle size within the above range has better adaptability to the positive electrode current collector, can have better adhesion under a certain modulus of the positive electrode current collector, further improve the stability of the positive electrode sheet, enable the secondary battery to have a higher passing rate in safety tests, and at the same time can further reduce the voltage drop of the secondary battery, further improve the low-temperature rate performance of the secondary battery, so that the secondary battery has better low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, while also having better low-temperature discharge performance, low-temperature rate performance and safety performance.

[0019] The second aspect of the present application provides an electronic device, wherein the electronic device includes the secondary battery provided by the first aspect of the present application.

[0020] The present application provides a secondary battery and an electronic device. The secondary battery includes an electrolyte and a separator. The electrolyte includes a lithium salt additive and ethylene glycol bis(propionitrile) ether. Based on the total mass of the electrolyte, the mass percentage content of the lithium salt additive is A%, and the mass percentage content of ethylene glycol bis(propionitrile) ether is B%, 0.035 ≤ A / B ≤ 20; the lithium salt additive satisfies at least one of the following characteristics: a. The lithium salt additive includes lithium bis(fluorosulfonyl)imide, 0.1 ≤ A ≤ 2.5; b. The lithium salt additive includes lithium tetrafluoroborate, 0.1 ≤ A ≤ 2.5; the separator includes a substrate layer, and the porosity of the substrate layer is P%, 15 ≤ P ≤ 35. The present application uses an electrolyte including a lithium salt additive and ethylene glycol bis(propionitrile) ether. The chelating effect of ethylene glycol bis(propionitrile) ether can adsorb the ions after the solvation of the lithium salt additive, and a CEI film can be formed at the interface between the positive electrode sheet and the electrolyte. By adjusting the values of A / B and A within the scope of the present application, the CEI film can have good mechanical strength and chemical stability, and good denseness and uniformity, which can inhibit the formation of electrolyte side reactions and reduce the generation of interface gas. At the same time, by adjusting the porosity of the separator substrate layer within the scope of the present application, the CEI film and the separator at the interface can have compatible ion permeability and electronic insulation, so that the secondary battery of the present application has good low-temperature floating charge performance, safety performance and overcharge resistance performance under high temperature and high pressure.

[0021] Of course, it is not necessary for any product or method implementing the present application to achieve all the above advantages simultaneously. Detailed Description of the Embodiments

[0022] Next, the technical solutions in the present application will be clearly and completely described in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0023] The first aspect of the present application provides a secondary battery. The secondary battery includes an electrolyte and a separator. The electrolyte includes a lithium salt additive and ethylene glycol bis(propionitrile) ether. Based on the total mass of the electrolyte, the mass percentage of the lithium salt additive is A%, and the mass percentage of ethylene glycol bis(propionitrile) ether is B%, where 0.035 ≤ A / B ≤ 20. The lithium salt additive satisfies at least one of the following characteristics: a. The lithium salt additive includes lithium bis(fluorosulfonyl)imide, and 0.1 ≤ A ≤ 2.5; b. The lithium salt additive includes lithium tetrafluoroborate, and 0.1 ≤ A ≤ 2.5. The separator includes a substrate layer, and the porosity of the substrate layer is P%, where 15 ≤ P ≤ 35. For example, A / B can be 0.035, 0.04, 0.047, 0.05, 0.09, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range composed of any two of these values; A can be 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, 1.0, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.1, 2.2, 2.3, 2.5, or a range composed of any two of these values; P can be 15, 17, 19, 20, 22, 24, 25, 26, 28, 30, 31, 32, 33, 34, 35, or a range composed of any two of these values. In the present application, the substrate layers with different porosities can be obtained by purchase, and then tested by the test methods of the above parameters provided in the following text of the present application to select the required substrate layer.

[0024] When the value of A / B is too small, for example, less than 0.035, the content of the lithium salt additive is low, and it is difficult to form a CEI film with good mechanical strength and chemical stability, and the effect of inhibiting the formation of side reactions of the electrolyte is poor, making it difficult to improve the low-temperature floating charge performance, safety performance and overcharge resistance performance under high temperature and high pressure of the secondary battery. When the value of A / B is too large, for example, greater than 20, the content of the lithium salt additive is too high, which will make the stability of the CEI film worse, the effect of inhibiting the occurrence of side reactions of the electrolyte worse, and the compactness of the CEI film too high, affecting the transmission of lithium ions, resulting in an increase in by-products, which is not conducive to improving the low-temperature floating charge performance, safety performance and overcharge resistance performance under high temperature and high pressure of the secondary battery. When the value of P is too small, for example, less than 15, there are fewer pores on the base material layer of the separator, and the ion permeability is poor, which is not conducive to improving the low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure of the secondary battery. When the value of P is too large, for example, greater than 35, there are too many pores on the base material layer of the separator, which will increase the risk of internal short circuit of the secondary battery and is not conducive to improving the safety performance of the secondary battery. In the present application, an electrolyte including a lithium salt additive and ethylene glycol bis(propionitrile) ether is used. The chelating effect of ethylene glycol bis(propionitrile) ether can adsorb the ions after the lithium salt additive is solvated, and a CEI film can be formed at the interface between the positive electrode sheet and the electrolyte. By controlling the values of A / B and A within the scope of the present application, the CEI film can have good mechanical strength and chemical stability, and good compactness and uniformity, which can inhibit the formation of side reactions of the electrolyte, reduce the generation of interface gas. At the same time, by controlling the porosity of the separator base material layer within the scope of the present application, the CEI film at the interface and the separator can have compatible ion permeability and electronic insulation, so that the secondary battery of the present application has good low-temperature floating charge performance, safety performance and overcharge resistance performance under high temperature and high pressure.

[0025] In some embodiments, more preferably, 0.047 ≤ A / B ≤ 10. By controlling the value of A / B within the above range, the mechanical strength and chemical stability of the CEI film formed by the lithium salt additive and ethylene glycol bis(propionitrile) ether can be further improved, making the ion permeability and electronic insulation of the CEI film more compatible, so as to further improve the low-temperature floating charge performance, safety performance and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0026] In some embodiments, even more preferably, 0.047 ≤ A / B ≤ 5. By controlling the value of A / B within the above range, the mechanical strength and chemical stability of the CEI film formed by the lithium salt additive and ethylene glycol bis(propionitrile) ether can be further improved, making the compatibility between the ion permeability and electronic insulation of the CEI film better, so as to further improve the low-temperature floating charge performance, safety performance and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0027] In some embodiments, more preferably, 15 ≤ P ≤ 25. By regulating the value of P within the above range, the CEI film and the separator can simultaneously have better electron insulation and ion permeability, and the separator itself meets certain structural strength and stability. At the same time, by using the electrolyte in the present application, the risk of separator deformation can be reduced, which is beneficial to improving the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0028] In some embodiments, the lithium salt additive includes lithium bis(fluorosulfonyl)imide (LiFSI), and 0.1 ≤ A ≤ 2.5. When the lithium salt additive of the present application includes lithium bis(fluorosulfonyl)imide and the value of A is regulated within the above range, it is beneficial to uniformly form a CEI film with good stability, good compactness, and relatively thin thickness under high pressure, which is beneficial to improving the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0029] In some embodiments, the lithium salt additive includes lithium tetrafluoroborate, and 0.1 ≤ A ≤ 2.5. When the lithium salt additive of the present application includes lithium tetrafluoroborate and the value of A is regulated within the above range, it is beneficial to uniformly form a CEI film with good stability, good compactness, and relatively thin thickness under high pressure, which is beneficial to improving the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0030] In some embodiments, the lithium salt additive includes lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate, and 0.1 ≤ A ≤ 2.5. In some embodiments, the mass ratio of lithium bis(fluorosulfonyl)imide to lithium tetrafluoroborate is 1:(0.5 to 1.5). When the lithium salt additive of the present application includes lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate and the value of A is regulated within the above range, lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate can produce a synergistic effect, and can uniformly form a CEI film with better stability, more appropriate compactness, and relatively thin thickness under high pressure, and can make the flow rate of lithium ions within a suitable range, so that the secondary battery has better low-temperature floating charge performance and safety performance, and at the same time has better overcharge resistance performance under high temperature and high pressure.

[0031] In some embodiments, 0.005 ≤ B ≤ 2.9. For example, B can be 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, 2.2, 2.5, 2.7, 2.9 or a range composed of any two of these values. By regulating the value of B within the above range, it is beneficial to the chelating effect of ethylene glycol bis(propionitrile) ether, so that the lithium salt additive and ethylene glycol bis(propionitrile) ether can form a CEI film with good stability, good compactness, and relatively thin thickness, which is beneficial to improving the low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure of the secondary battery.

[0032] In some embodiments, the electrolyte further includes 4,4'-diphenylether dicarboxylic acid. Based on the total mass of the electrolyte, the mass percentage content of 4,4'-diphenylether dicarboxylic acid is C%, where 0.5 ≤ C ≤ 2.5. For example, C can be 0.5, 1.0, 1.2, 1.5, 1.7, 2.0, 2.2, 2.5, or a range composed of any two of these values. By using an electrolyte that further includes 4,4'-diphenylether dicarboxylic acid and controlling the value of C within the above range, 4,4'-diphenylether dicarboxylic acid can form a more stable, more uniform, and thinner CEI film with the lithium salt additive and ethylene glycol bis(propionitrile) ether. At the same time, it can form a stable and thin solid electrolyte interface film (SEI film) at the interface between the negative electrode sheet and the electrolyte, and enable both the formed SEI film and CEI film to have good electron insulation and ion permeability, thereby facilitating the improvement of the low-temperature floating charge performance, safety performance, and overcharge resistance under high temperature and high pressure of the secondary battery.

[0033] In some embodiments, the electrolyte further includes methylene methanedisulfonate. Based on the total mass of the electrolyte, the mass percentage content of methylene methanedisulfonate is D%, where 0.01 ≤ D ≤ 0.5. For example, D can be 0.01, 0.02, 0.05, 0.06, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, 0.33, 0.35, 0.37, 0.4, 0.43, 0.45, 0.48, 0.5, or a range composed of any two of these values. By using an electrolyte that further includes methylene methanedisulfonate and controlling the value of D within the above range, methylene methanedisulfonate can form a more stable, more uniform, and thinner CEI film with the lithium salt additive and ethylene glycol bis(propionitrile) ether, and enable the formed SEI film to have good electron insulation and ion permeability, thereby facilitating the improvement of the low-temperature floating charge performance, safety performance, and overcharge resistance under high temperature and high pressure of the secondary battery.

[0034] In some embodiments, the electrolyte further includes 4-isopropylphenyl diphenyl phosphate. Based on the total mass of the electrolyte, the mass percentage of 4-isopropylphenyl diphenyl phosphate is G%, where 1.5 ≤ G ≤ 4.5. For example, G can be 1.5, 1.8, 2.0, 2.2, 2.4, 2.5, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.5, or a range composed of any two of these values. By using an electrolyte that further includes 4-isopropylphenyl diphenyl phosphate and controlling the value of G within the above range, 4-isopropylphenyl diphenyl phosphate can help form a dense and uniform SEI film at the interface between the negative electrode sheet and the electrolyte, inhibit the solvent decomposition of the electrolyte during the reduction process, and simultaneously reduce the risk of lithium dendrite deposition on the surface of the negative electrode sheet. Thereby, while improving the low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure of the secondary battery, it can also improve the high-temperature storage performance and low-temperature intermittent cycling performance of the secondary battery, and can further improve the safety performance of the secondary battery.

[0035] In some embodiments, the electrolyte further includes other additives. The other additives include at least one of vinylene sulfate (DTD), vinylene sulfite (VC), or 1,3-propane sultone; further, the other additives further include at least one of methyl fluoromethyl carbonate, methyl difluoromethyl carbonate, methyl trifluoromethyl carbonate, methyl trifluoroethyl carbonate, or bis(trifluoroethyl) carbonate. The present application does not particularly limit the content of the other additives, as long as the object of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage of the other additives is 0.2% to 2.5%.

[0036] In some embodiments, in addition to the above lithium salt additives, the electrolyte further includes other ionizable lithium salts. The other ionizable lithium salts include at least one of LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiC(CF3SO2)3, or LiC4BO8. The present application does not particularly limit the content of the other ionizable lithium salts, as long as the object of the present application can be achieved. In some embodiments, based on the total mass of the electrolyte, the mass percentage of the other ionizable lithium salts is 8% to 15%, preferably 8% to 12%, and further preferably 8% to 10%. Controlling the content of the other ionizable lithium salts within the above range can enable the electrolyte to have an appropriate number of mobile lithium ions, keep the viscosity of the electrolyte within an appropriate range, improve the migration rate of lithium ions, and enhance the performance of the secondary battery.

[0037] In some embodiments, the electrolyte further includes propyl propionate. The present application does not particularly limit the content of propyl propionate, as long as the object of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage content of propyl propionate is 22% to 40%. In some embodiments, the electrolyte further includes fluoroethylene carbonate (FEC). The present application does not particularly limit the content of fluoroethylene carbonate, as long as the object of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage content of fluoroethylene carbonate is 0.5% to 10%. In some embodiments, the electrolyte further includes a trinitrile compound. The present application does not particularly limit the content of the trinitrile compound, as long as the object of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage content of the trinitrile compound is 0.1% to 5%. In some embodiments, the trinitrile compound includes at least one of 1,2,6-hexanetricarbonitrile, 1,3,6-hexanetricarbonitrile, or 1,3,5-pentanetricarbonitrile.

[0038] In some embodiments, the electrolyte further includes a fluoroether. The present application does not particularly limit the content of the fluoroether, as long as the object of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage content of the fluoroether is 0.5% to 4.5%.

[0039] In some embodiments, the electrolyte further includes a non-aqueous solvent. The present application does not particularly limit the non-aqueous solvent, as long as the object of the present application can be achieved. For example, the non-aqueous solvent may include, but is not limited to, at least one of a carbonate compound, a carboxylate compound, an ether compound, or other organic solvents.

[0040] The above-mentioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above-mentioned chain carbonate compounds may include, but are not limited to, at least one of diethyl carbonate (DEC), ethyl propionate (EP), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or ethyl methyl carbonate (EMC). The above-mentioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The above-mentioned fluorinated carbonate compounds may include, but are not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above-mentioned carboxylate compounds may include, but are not limited to, at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, or methyl formate. The above-mentioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above-mentioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the object of this application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage content of the non-aqueous solvent is 48% to 69%. For example, the mass percentage content of the non-aqueous solvent is 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, or a range composed of any two of these values.

[0041] In some embodiments, the separator further includes a first coating on at least one surface of the substrate layer. The first coating includes an adhesive layer, and the average wall thickness between adjacent pores in the adhesive layer is T nm, where 2 ≤ T ≤ 450. For example, T can be 2, 10, 20, 50, 80, 100, 120, 150, 180, 200, 250, 300, 320, 350, 380, 400, 420, 450, or a range composed of any two of these values. If the average wall thickness between adjacent pores in the adhesive layer of the separator is too low, for example, less than 2 nm, it is difficult to achieve in the process. When the average wall thickness between adjacent pores in the adhesive layer is within the scope of this application, the adhesion uniformity between the separator and the electrode can be good, reducing the risk of electrode detachment caused by large differences in the bonding strength in local areas, thereby reducing the phenomenon of lithium deposition and black spots in some areas due to the differential local rate of lithium ion transport. This enables the secondary battery of this application to have good low-temperature floating charge performance and overcharge resistance under high temperature and high pressure, while also having good low-temperature rate performance and safety performance. At the same time, when the average wall thickness between adjacent pores in the adhesive layer is within the above range, the strength of the separator is relatively uniform, enabling the secondary battery to have a higher passing rate in safety tests and better safety performance.

[0042] In some embodiments, the separator further includes a second coating on at least one surface of the substrate layer. On the surface of the second coating, in a 2 μm × 2 μm area, the ratio of the apparent concentration of nitrogen element to the apparent concentration of carbon element is Y, where 1 ≤ Y ≤ 8. For example, Y can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range composed of any two of these values. When the ratio Y of the apparent concentration of nitrogen element to the apparent concentration of carbon element on the surface of the second coating of the separator is within the scope of this application, there are nitrogen-containing functional groups in the separator, which can play a stable binding role with the metal ions of the positive electrode active material, reducing the binding energy, so that the structural stability of the separator and the positive electrode is better. This enables the secondary battery to have a higher passing rate in safety tests, and at the same time can reduce the gas generation amount and self-discharge during the cycling of the secondary battery, reducing the voltage drop. Thus, the secondary battery has good low-temperature floating charge performance and overcharge resistance under high temperature and high pressure, while also having good low-temperature discharge performance and safety performance.

[0043] In some embodiments, 1 ≤ Y ≤ 4. By regulating the ratio Y of the apparent nitrogen element concentration to the apparent carbon element concentration within the above range, the nitrogen-containing functional groups of the separator membrane can better and more stably bind to the metal ions on the cathode active material, further reducing the binding energy, thereby making the structure of the separator membrane and the cathode electrode sheet more stable, enabling the secondary battery to have a higher passing rate in safety tests, and at the same time being able to further reduce the gas generation amount and self-discharge during the cycling of the secondary battery, reducing the voltage drop, so that the secondary battery has better low-temperature floating charge performance and overcharge resistance under high temperature and high pressure, while also having better low-temperature discharge performance and safety performance.

[0044] In some embodiments, the base material layer of the separator membrane includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene or ultra-high molecular weight polyethylene. In some embodiments, the base material layer of the separator membrane includes at least one of polyethylene or polypropylene, which has a good effect on preventing short circuits and can improve the safety performance of the secondary battery through the shut-off effect. The present application does not particularly limit the molecular weight of the base material layer as long as the object of the present application can be achieved.

[0045] In some embodiments, the separator membrane further includes an inorganic coating, and the inorganic coating is disposed on at least one surface of the separator membrane. In some embodiments, the separator membrane further includes an inorganic coating, and along the thickness direction of the separator membrane, the inorganic coating is disposed between the base material layer and the first coating. In some embodiments, the separator membrane further includes an inorganic coating, and along the thickness direction of the separator membrane, the inorganic coating is disposed between the base material layer and the second coating. The inorganic coating includes inorganic particles and a binder, and the inorganic particles are selected from at least one of aluminum oxide (Al2O3), silicon dioxide (SiO2), magnesium oxide (MgO), titanium dioxide (TiO2), hafnium dioxide (HfO2), tin dioxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application does not particularly limit the binder as long as the object of the present application can be achieved. For example, the binder is selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyethylene ether, polytetrafluoroethylene or polyhexafluoropropylene. The separator membrane with an inorganic coating can improve the heat resistance, antioxidant performance and electrolyte infiltration performance of the separator membrane, and enhance the adhesion between the separator membrane and the electrode sheet. The present application does not particularly limit the mass ratio of the inorganic particles to the binder as long as the object of the present application can be achieved.

[0046] In some embodiments, the adhesive layer comprises inorganic particles and a binder. The binder comprises a high-temperature resistant resin, and the high-temperature resistant resin comprises at least one of a high melting point crystalline polymer or a high-temperature resistant amorphous polymer. The high melting point crystalline polymer comprises at least one of polypropylene, poly(4-methyl-1-pentene), polytetrafluoroethylene, or polyvinylidene fluoride. The high-temperature resistant amorphous polymer comprises a cycloolefin copolymer. Based on the mass of the substrate layer, the mass percentage Z% of the high-temperature resistant resin is 2.5% to 9%. For example, the mass percentage Z% of the high-temperature resistant resin can be 2.5%, 3%, 5%, 7%, 8%, 9%, or any range composed of any two of these values. Using the separator film with the adhesive layer comprising the above high-temperature resistant resin and controlling the mass percentage of the high-temperature resistant resin within the above range is beneficial to increasing the melting break temperature and strength of the separator film and improving the high-temperature performance of the secondary battery. There is no particular limitation on the inorganic particles in this application as long as the purpose of this application can be achieved. For example, the inorganic particles can be at least one of the above inorganic particles.

[0047] In some embodiments, the preparation steps of the adhesive layer include: mixing the inorganic particles and the binder according to a mass ratio, then adding a first solvent and stirring evenly to obtain an adhesive layer coating solution with a solid content of 3-14 wt%, coating it on the surface of the separator film, immersing it in a coagulation liquid for 15 s to 100 s, and then drying it at a temperature of 20°C to 100°C for 0.5 h to 6 h to obtain a separator film with an adhesive layer. There is no particular limitation on the first solvent in this application as long as the purpose of this application can be achieved. For example, the first solvent is N-methylpyrrolidone. There is no particular limitation on the coagulation liquid in this application as long as the purpose of this application can be achieved. For example, the coagulation liquid comprises a second solvent and a third solvent. Based on the total mass of the coagulation liquid, the mass percentage of the second solvent is 30% to 50%, and the balance is the third solvent. There is no particular limitation on the types of the second solvent and the third solvent in this application as long as the purpose of this application can be achieved. For example, the second solvent is N-methylpyrrolidone and the third solvent is deionized water. In this application, the average wall thickness T nm between adjacent pores in the adhesive layer can be controlled by adjusting parameters such as the mass ratio of the inorganic particles and the binder and the solid content of the adhesive layer coating solution in the preparation steps of the adhesive layer. Specifically, increasing the mass ratio of the inorganic particles and the binder in the adhesive layer, T will decrease; increasing the solid content of the adhesive layer coating solution, T will increase. In some embodiments, the mass ratio M1:M2 of the inorganic particles and the binder in the adhesive layer is 75:25 to 98:2; for example, M1:M2 can be 75:25, 80:20, 85:15, 90:10, 95:5, 98:2, or any range composed of any two of these values.

[0048] In some embodiments, the second coating includes a nitrogen-containing material and a binder. In some embodiments, the second coating further includes inorganic particles. The present application does not particularly limit the contents of the nitrogen-containing material, the binder, and the inorganic particles, as long as the objectives of the present application can be achieved. For example, based on the total mass of the nitrogen-containing material, the binder, and the inorganic particles, the mass percentage content of the nitrogen-containing material is 60% to 95%, the mass percentage content of the binder is 0.5% to 10%, and the mass percentage content of the inorganic particles is 0% to 30%. The present application does not particularly limit the type of the nitrogen-containing material, as long as the objectives of the present application can be achieved. For example, the nitrogen-containing material is selected from at least one of cyanuric chloride, pyrazinamide, 5,6-diamino-2,3-dicyanopyrazine, sym-triaminotriazine, or 2,3-dicyanopyrazine. The present application does not particularly limit the types of the binder and the inorganic particles, as long as the objectives of the present application can be achieved. For example, it may be at least one of the above-mentioned binder and the above-mentioned inorganic particles.

[0049] In some embodiments, the thickness of the separator membrane can be 3 μm to 480 μm.

[0050] In some embodiments, the secondary battery further includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector, the dyne value of the positive electrode current collector is E (dyn / cm), the positive electrode active material layer includes a positive electrode active material, the average particle size of the positive electrode active material is F μm, and 0.5 ≤ E / F ≤ 30. For example, E / F can be 0.5, 1, 3, 5, 7, 8, 10, 12.5, 13, 14, 15, 18, 20, 22, 25, 27, 29, 30, or a range composed of any two of these values. In the present application, the above-mentioned "positive electrode active material layer located on at least one surface of the positive electrode current collector" means that the positive electrode active material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the positive electrode current collector, or a partial area of the surface of the positive electrode current collector. The present application has no particular limitation, as long as the objectives of the present application can be achieved. By adjusting the ratio E / F of the dyne value of the positive electrode current collector and the average particle size of the positive electrode active material within the scope of the present application, the surface tension of the positive electrode current collector itself is adapted to the positive electrode active material particles used, so that the force between the two is appropriate, which can make the positive electrode plate have a higher strength, maintain good structural stability when using the electrolyte of the present application, enable the secondary battery to have a higher passing rate in the safety test, and at the same time can reduce the gas generation amount of the secondary battery during the cycling process and reduce the voltage drop, so that the secondary battery has good low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, and also has good low-temperature discharge performance and safety performance.

[0051] In some embodiments, 1 ≤ E / F ≤ 12.5. When the ratio E / F of the dyne value of the positive electrode current collector to the average particle size of the positive electrode active material is within the above range, the positive electrode sheet can have higher strength and maintain better structural stability when using the electrolyte of the present application. As a result, the secondary battery has better low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, while also having better low-temperature discharge performance and safety performance.

[0052] In some embodiments, 25 ≤ E ≤ 30. For example, E can be 25, 26, 27, 28, 29, 30, or a range composed of any two of these values. When the dyne value of the positive electrode current collector is within the above range, the positive electrode current collector can be more adapted to the positive electrode active material, further improving the structural stability of the positive electrode sheet. As a result, the secondary battery has better low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, while also having better low-temperature discharge performance and safety performance.

[0053] In some embodiments, the specific surface area (BET) of the positive electrode active material is S m 2 / g, 0.05 ≤ S ≤ 0.86. For example, S can be 0.05, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.86, or a range composed of any two of these values. In the present application, the positive electrode active materials with the above different specific surface areas can be obtained by purchase, and then tested in combination with the test methods for the above parameters provided below in the present application to select the required positive electrode active materials. The positive electrode active materials with specific surface areas within the above range have an active specific surface area and structural strength adapted to the above electrolyte, which is beneficial to improving the structural stability of the positive electrode sheet, can enable the secondary battery to have a high passing rate in safety tests, while also being able to reduce the voltage drop of the secondary battery, improve the low-temperature rate performance of the secondary battery, so that the secondary battery has better low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, while also having better low-temperature discharge performance, low-temperature rate performance and safety performance.

[0054] In some embodiments, the positive electrode active material contains aluminum. The present application does not particularly limit the preparation method of the positive electrode active material containing aluminum, as long as the object of the present application can be achieved. For example, it can be obtained by coating alumina on the surface of the positive electrode active material. If the CEI film decomposes, it is difficult to reduce the formation of interfacial side reactions, which will lead to an increase in interfacial gas generation, intense reactions between the positive and negative electrodes and the electrolyte, and the generation of more interfacial by-products, resulting in poor low-temperature rate performance and severe self-discharge of the secondary battery, and an increase in voltage drop. The positive electrode active material contains aluminum, and the aluminum participates in the formation of the interfacial CEI film, which can improve the Young's modulus of the interfacial CEI film, improve the strength and hardness of the CEI film, reduce the influence of the generated gas on the CEI film, reduce the risk of CEI film decomposition, improve the self-discharge of the secondary battery, reduce the voltage drop, so that the secondary battery has good low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, while also having good low-temperature discharge performance, low-temperature rate performance and safety performance.

[0055] In some embodiments, 1≤F≤30. For example, F can be 1, 4, 5, 7, 10, 12, 15, 18, 20, 22, 25, 28, 30 or a range composed of any two of these values. In the present application, the positive electrode active materials with different average particle sizes can be obtained by purchase, and then tested by combining the test methods of the above parameters provided in the following text of the present application, and the required positive electrode active materials can be selected. The positive electrode active material with an average particle size within the above range has better adaptability to the positive electrode current collector, can have better adhesion under a certain modulus of the positive electrode current collector, further improve the stability of the positive electrode plate, make the secondary battery have a higher passing rate in the safety test, and at the same time can further reduce the voltage drop of the secondary battery, further improve the low-temperature rate performance of the secondary battery, so that the secondary battery has good low-temperature floating charge performance and overcharge resistance performance under high temperature and high pressure, while also having better low-temperature discharge performance, low-temperature rate performance and safety performance.

[0056] The present application does not particularly limit the positive electrode current collector, as long as the object of the present application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or composite current collector (such as aluminum-carbon composite current collector), etc. The present application does not particularly limit the thickness of the positive electrode current collector and the positive electrode material layer, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector can be 1μm to 200μm, and the thickness of the positive electrode material layer can be 10μm to 500μm, for example, it can be 10μm, 20μm, 40μm, 90μm, 400μm, 490μm, 500μm or a range composed of any two of these values.

[0057] The present application has no particular limitation on the positive electrode active material, as long as the object of the present application can be achieved. In some embodiments, the positive electrode active material may include, but is not limited to, at least one of lithium cobaltate (LiCoO2), lithium manganate, lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganate (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate or lithium nickel manganate. In some embodiments, the positive electrode active material is lithium cobaltate or lithium iron phosphate. In some embodiments, the above positive electrode active material may be subjected to doping and / or coating treatment. In some embodiments, the above positive electrode active material is subjected to aluminum doping and / or aluminum coating treatment.

[0058] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent. The present application has no particular limitation on the types of the positive electrode binder and the positive electrode conductive agent, as long as the object of the present application can be achieved. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinyl pyrrolidone, polyethylene ether, polytetrafluoroethylene or polyhexafluoropropylene. For example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), graphene, carbon nanotubes or carbon fibers. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The carbon nanotubes may include, but is not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The carbon fibers may include, but is not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The present application has no particular limitation on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0059] In some embodiments, the surface of the positive electrode active material includes an alumina coating layer, and the thickness of the alumina coating layer is 1 μm to 1.5 μm.

[0060] In some embodiments, the surface of the positive electrode active material includes at least one of lithium phosphate, lithium niobate or melamine, and the mass is 5% to 10% of the mass of the positive electrode material layer. In some embodiments, the surface of the positive electrode active material has polyvinylidene fluoride of α crystal form. In some embodiments, the surface of the positive electrode active material includes at least one of lithium dihydrogen phosphate or aluminum dihydrogen phosphate, and the mass is 5% to 20% of the mass of the positive electrode material layer.

[0061] In some embodiments, the secondary battery further includes a negative electrode plate, and the separator is located between the positive electrode plate and the negative electrode plate. In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The above "the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or can be disposed on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. There is no special limitation in the present application, as long as the purpose of the present application can be achieved. There is no special limitation on the negative electrode current collector in the present application, as long as the purpose of the present application can be achieved. For example, it can include at least one of copper foil, nickel foil or carbon-based current collector. There is no special limitation on the thickness of the negative electrode current collector in the present application, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector can be 1 μm to 200 μm. There is no special limitation on the thickness of the negative electrode active material layer in the present application, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode active material layer can be 10 μm to 500 μm. It should be understood that these are only exemplary, and other suitable thicknesses can also be adopted.

[0062] In some embodiments, the negative electrode active material layer includes a negative electrode active material. There is no special limitation on the negative electrode active material in the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite or silicon-based materials. In some embodiments, the silicon-based material includes at least one of silicon, silicon oxide, silicon carbide or silicon alloy.

[0063] In some embodiments, the negative electrode material layer may further include a negative electrode conductive agent and / or a negative electrode binder. The present application does not particularly limit the types of the negative electrode conductive agent and the negative electrode binder, as long as the purpose of the present application can be achieved. For example, the negative electrode conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), graphene, carbon nanotubes, or carbon fibers. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The carbon nanotubes may include, but is not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The carbon fibers may include, but is not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. For example, the negative electrode binder may include, but is not limited to, at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylates, polyacrylate esters, polyvinylpyrrolidone, polyimide, polysiloxane, or styrene-butadiene rubber. It should be understood that the above materials are only exemplary, and the negative electrode material layer may adopt any other suitable materials. 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 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. In some embodiments, the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode material layer may be (80-99):(0.5-10):(0.5-10). It should be understood that this is only exemplary and does not limit the present application.

[0064] In some embodiments, the negative electrode material layer may further include a thickening agent. The present application does not particularly limit the type of the thickening agent, as long as the purpose of the present application can be achieved. For example, the thickening agent may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickening agent in the negative electrode 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.

[0065] The secondary battery further includes a housing for accommodating the positive electrode plate, the separator, the negative electrode plate, and the electrolyte, as well as other components known in the field of secondary batteries. The present application does not limit the above other components. The present application does not particularly limit the housing, which may be a housing well-known in the art as long as the purpose of the present application can be achieved. For example, the housing may be a hard-shell housing or a flexible housing. The material of the hard-shell housing may be metal. The present application does not limit the type of the metal, and a metal hard-shell housing known in the art may be adopted as long as the purpose of the present application can be achieved. The flexible housing may be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0066] In some embodiments, the secondary battery is a lithium-ion battery, but the present application is not limited thereto.

[0067] The preparation process of the secondary battery of the present application is well-known to those skilled in the art, and there is no special limitation in the present application. For example, the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and winding, folding, etc. as needed to obtain a wound electrode assembly, placing the electrode assembly into a housing, injecting electrolyte into the housing and sealing it to obtain a secondary battery. Or, stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly, placing the electrode assembly into a housing, injecting electrolyte into the housing and sealing it to obtain a secondary battery. In addition, an overcurrent protection element, a guide plate, etc. may be placed in the housing as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0068] In some embodiments, taking a lithium-ion battery as an example, the positive electrode sheet, the separator, and the negative electrode sheet are wound or stacked in sequence to form an electrode assembly, and then it is placed into a housing such as an aluminum-plastic film, electrolyte is injected, and it is formed and encapsulated to make a lithium-ion battery.

[0069] The second aspect of the present application provides an electronic device, wherein the electronic device includes the secondary battery provided by the first aspect of the present application. Thus, the electronic device provided by the present application has good use performance. The present application does not particularly limit the type of the electronic device, and it may be any electronic device known in the prior art. In some embodiments, the electronic device may include but is not limited to a laptop computer, a pen input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset stereo earphone, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0070] Examples

[0071] Hereinafter, examples and comparative examples are given to illustrate the embodiments of the present application more specifically. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0072] Testing methods and equipment:

[0073] Component test of electrolyte:

[0074] The electrolyte was obtained by disassembling the lithium-ion battery. The components of the electrolyte were tested using a gas chromatography-mass spectrometer (GC-MS, model: Agilent GC7890A), and the mass percentage contents of the lithium salt additive, ethylene glycol bis(propionitrile) ether, 4,4'-diphenylether dicarboxylic acid, and methylene methanesulfonate in the electrolyte components were calculated using the external standard method.

[0075] Porosity test of the separator substrate layer:

[0076] The separator was obtained by disassembling the lithium-ion battery. The coating on the surface of the separator was scraped off to obtain the substrate layer of the separator. At a test temperature of 30 °C, the substrate layer was wrapped flat with A4 paper and laid flat on the die, and then stamped with a stamping machine. First, the thickness of the substrate layer was measured using a micrometer, and the apparent volume V1 of the substrate layer was calculated based on the surface area and thickness of the substrate layer. Then, the true volume V2 of the substrate layer was tested using a true density meter (model AccuPycⅡ), and the porosity P% of the substrate layer was obtained as P%=(V1 - V2) / V1×100%.

[0077] Average wall thickness test between adjacent pores in the separator adhesive layer:

[0078] The separator was obtained by disassembling the lithium-ion battery. A 1μm×1μm area of the separator adhesive layer was tested using a scanning electron microscope (SEM), and the wall thickness between every two adjacent pores among 25 adjacent pores with uniform distribution was measured, and the average value was calculated to obtain the average wall thickness T nm between adjacent pores in the adhesive layer.

[0079] Apparent concentration ratio test of nitrogen and carbon elements:

[0080] The separator was obtained by disassembling the lithium-ion battery. The surface of the second coating of the separator was measured using an energy dispersive spectrometer (EDS, model: EDAX Octane SDD). At 30 °C, the apparent concentration of nitrogen and the apparent concentration of carbon in a 2μm×2μm area were tested, and the ratio Y of the apparent concentration of nitrogen to the apparent concentration of carbon was Y = apparent concentration of nitrogen / apparent concentration of carbon.

[0081] Dyne value test of the positive current collector:

[0082] Dyne pens with different dyne values (manufacturer: ACCU) were used to draw lines on the surface of the positive current collector along the running direction of the tape and its perpendicular direction. If the line does not shrink within 3 s, this dyne value is reached. The dyne pen with the same dyne value was tested three times. If the line does not shrink within 3 s each time, then this dyne value is the surface tension of the positive current collector. For the positive current collector in the lithium-ion battery, since the positive current collector at the tab position is relatively flat, the lithium-ion battery was disassembled, the tab was torn off, and the positive current collector at the tab position was taken for testing.

[0083] Average particle size test of the positive active material:

[0084] The lithium-ion battery was disassembled to obtain the positive electrode plate. The SEM photograph of the positive electrode plate was taken using a scanning electron microscope to observe the positive active material particles. Using image analysis software, 30 positive active material particles were randomly selected from the SEM photograph, and the area of each particle was determined. Assuming the particle is spherical, the particle size D (diameter) was calculated through the following formula: D = 2×(S1 / π) 1 / 2 , where S1 is the area of the particle; the arithmetic mean of the particle sizes of the obtained 30 particles was calculated to obtain the average particle size of the positive active material.

[0085] Measurement of the specific surface area of the positive active material:

[0086] In accordance with the national standard "Determination of Specific Surface Area of Solid Materials by Gas Adsorption BET Method" (GB / T 19587-2017), a specific surface area analyzer (model TristarⅡ3020M) was used to measure the specific surface area of the positive active material by the nitrogen adsorption method.

[0087] Detection of aluminum in the positive active material:

[0088] The lithium-ion battery was disassembled to obtain the positive electrode plate. The internal area of the positive active material of the positive electrode plate was tested using EDS to detect whether it contains aluminum element.

[0089] Low-temperature floating charge performance test:

[0090] The lithium-ion battery was placed in a constant temperature oven at 0°C and left standing for 30 minutes to make the lithium-ion battery reach a constant temperature. It was charged at a constant current of 1C until the voltage reached 4.2V, then charged at a constant voltage until the current reached 0.05C, and then discharged at a constant current of 1C until the voltage reached 2.8V. The discharge capacity was recorded and denoted as the initial discharge capacity of the lithium-ion battery. Then it was charged at a constant current of 0.5C until the voltage reached 4.2V, and then charged at a constant voltage until the current reached 0.05C. The lithium-ion battery was transferred to a constant temperature oven at 25°C and charged at a constant voltage of 4.2V for 10 days. After 10 days, the lithium-ion battery was transferred to a constant temperature oven at 0°C and left standing for 60 minutes, and then discharged at a constant current of 1C until the voltage reached 2.8V. Then it was charged at a constant current of 1C until the voltage reached 4.2V, then charged at a constant voltage until the current reached 0.05C, and then discharged at a constant current of 1C to 2.8V. The discharge capacity was recorded and denoted as the recoverable capacity of the lithium-ion battery. The low-temperature floating charge capacity retention rate % = (initial discharge capacity - recoverable capacity) / initial discharge capacity × 100%.

[0091] Hot box test:

[0092] Charge the lithium-ion battery at a constant current of 0.5C to the cut-off voltage of 4.2V, then charge it at a constant voltage until the cut-off current is 200mA, and then let it stand for 5 minutes; Stick a temperature-sensing wire on the fully charged lithium-ion battery between the two tab ears, connect the two tab ears to monitor the voltage, and hang the lithium-ion battery vertically in the thermal chamber; The thermal chamber is heated to 145°C at a heating rate of 5°C and maintained for 60 minutes, and observe the state of the lithium-ion battery during the process. Each lithium-ion battery in each example or comparative example has 20 lithium-ion batteries as parallel samples for testing. Judgment criterion: If the lithium-ion battery does not catch fire or explode, it is considered to pass. Thermal chamber test pass rate (%) = number of passes in thermal chamber test / total number × 100%.

[0093] Overcharge test:

[0094] Under the condition of ambient temperature (60±5)°C, charge the lithium-ion battery at a constant current of 1C to a voltage of 4.2V, charge it at a constant voltage until the current is 0.05C, and then discharge it at a constant current of 1C to a voltage of 2.8V. Charge the discharged lithium-ion battery at a constant current of 0.25C to 10V and then change to constant voltage charging, and stop charging after 5 hours of charging. The passing standard is that the lithium-ion battery does not catch fire or explode. Each lithium-ion battery in each example or comparative example is tested 20 times, record the number of passes in the test, and the overcharge test pass rate (%) = number of passes in overcharge test / total number × 100%.

[0095] Lithium plating performance test:

[0096] Place the lithium-ion battery in an incubator at 10°C. After 60 minutes, charge it at a constant current of 2C to 4.2V, charge it at a constant voltage of 4.2V until the current is 0.05C, let it stand for 5 minutes, and then discharge it at a constant current of 0.5C to 2.5V. This is one cycle. After cycling 10 times according to the above charge and discharge process, charge it at a constant current of 2C to 4.2V, charge it at a constant voltage of 4.2V until the current is 0.05C, let it stand for 5 minutes, and then disassemble the lithium-ion battery to observe the lithium plating state on the surface of the negative electrode plate. The non-lithium-plated area on the surface is golden yellow, and the lithium-plated area is grayish white.

[0097] The judgment criteria for the degree of lithium plating of lithium-ion batteries are as follows: The lithium plating area of 0% means no lithium plating, that is, the degree of lithium plating is none. The lithium plating area greater than 0 and less than or equal to 2% means mild lithium plating, that is, the degree of lithium plating is mild. The lithium plating area greater than 2% and less than or equal to 20% means moderate lithium plating, that is, the degree of lithium plating is moderate. The lithium plating area greater than 20% and less than or equal to 100% means severe lithium plating, that is, the degree of lithium plating is severe, where the percentage of the lithium plating area is calculated based on the total area of the negative electrode material layer of the negative electrode plate.

[0098] Low-temperature rate performance test:

[0099] At 25°C, the lithium-ion battery is charged to 4.2V at 0.5C constant current, then charged to 0.05C at 4.2V constant voltage, and then discharged to 2.8V at 1C constant current, and the discharge capacity is recorded as D02; at 25°C, the lithium-ion battery is charged to 4.2V at 0.5C constant current, then charged to 0.05C at 4.2V constant voltage, the temperature is adjusted to -10°C, the lithium-ion battery is placed for 30 minutes, and then discharged to 2.8V at 1C constant current, and the discharge capacity is recorded as D2. -10°C 1C low temperature retention rate (%) = D2 / D02×100%.

[0100] Gas production test:

[0101] The lithium-ion battery was charged at 0.35C constant current at 25°C to a voltage of 4.2V, then charged at 4.2V constant voltage to a current of 0.05C, and then discharged at a constant current of 0.35C to a voltage of 2.5V. The discharge capacity was recorded as C0. At 25°C, the lithium-ion battery was charged at 0.35C constant current to a voltage of 4.2V, and then charged at 4.2V constant voltage to a current of 0.05C. At this time, the lithium-ion battery was fully charged, the volume of the lithium-ion battery was measured, and recorded as the volume of the lithium-ion battery before storage. The fully charged lithium-ion battery was stored in a thermostat at 45°C for 30 days, then removed from the thermostat, and the volume was measured after returning to room temperature. The amount of gas generated can be tested using an in-situ gas production meter, and the gas production can be determined by testing the change in the volume of the lithium-ion battery.

[0102] Low temperature voltage drop test:

[0103] At 25°C, charge the lithium-ion battery to 4.2V at 1C constant current, then charge to 0.05C at constant voltage, and then discharge to 3V at 1C constant current, and let it stand for 5 minutes, then test the voltage, which is the voltage before storage. After storing at 0°C for 24 hours, re-test the voltage, which is the voltage after storage. Low temperature voltage drop (V) = voltage before storage - voltage after storage.

[0104] Drop performance test:

[0105] The lithium-ion battery was placed in an environment of 25°C, charged at a constant current of 0.5C to a voltage of 4.2V, and then charged at a constant voltage of 4.2V to a cut-off current of 0.05C, and left to stand for 5 minutes to be fully charged; the lithium-ion battery was placed in a fixed fixture, and the appearance was inspected and photographed before and after the test; the battery was freely dropped to the floor using the fixture, and dropped once along the head and tail surfaces and once at the four corners from a drop height of 1.5m. A total of 6 rounds of tests were conducted, 1 round and 6 times, and the order of drop was: head, tail, right corner of the head, right corner of the tail, left corner of the head, and left corner of the tail (angle: 45±15°).

[0106] The voltage of the lithium-ion battery is measured before and after the drop test. The pass standard of the drop test is: no smoke, no leakage, and voltage drop <30mV. Among them, voltage drop = voltage value before drop test - voltage value after drop test. Twenty lithium-ion batteries are tested in each embodiment or comparative example, and the number of passed batteries is recorded. The drop test pass rate (%) = number of drop test passes / total number × 100%. For example, 90% means that 20 lithium-ion batteries are tested and 18 pass the drop test.

[0107] In this application, those skilled in the art will understand that "C" refers to the rated capacity of the finished lithium-ion battery when it leaves the factory. "1C" is the current value that fully discharges the capacity of the lithium-ion battery within 1 hour, "0.1C" is the current value that fully discharges the capacity of the lithium-ion battery within 10 hours, and other multiples are similar.

[0108] Example 1-1

[0109] <Preparation of positive electrode sheet>

[0110] Take 1.2g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) and add it to the ethanol solution. Start stirring. Take 1g of citric acid and add it. Stir and disperse for 2h to form a dispersed system. Weigh 50g of the positive electrode active material lithium cobalt oxide (LiCoO2, specific surface area Sm 2 / g is 0.20m 2 / g, average particle size Fμm is 20.00μm) is added to the above dispersion system, heated to 80°C and stirred for 48h to obtain a gel; the gel is placed in a vacuum drying oven at 115°C and dried for 50h, and the dried gel is ground, crushed and sieved, put into a 200mL crucible, and heated to 440°C at a rate of 5°C / min in a tubular furnace N2 atmosphere for sintering, and kept warm at this temperature for 4h to prepare alumina-coated positive electrode material lithium cobalt oxide; the temperature of the tubular furnace is reduced to 400°C, the N2 atmosphere is switched to O2 atmosphere, and the heat treatment is carried out for 4h to oxidize the carbon matrix to obtain Al2O3-coated lithium cobalt oxide LiCoO2, a lithium cobalt oxide positive electrode material containing a nano-alumina coating layer.

[0111] Mix lithium cobalt oxide LiCoO₂ coated with Al₂O₃, conductive agent Super P (conductive carbon black), and binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:2. Add N-methylpyrrolidone (NMP) and 2800 ppm of methyl acrylate as an additive containing acrylate. Stir evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 65 wt%. Uniformly coat the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm and a surface tension value E dyn / cm of 26 dyn / cm. Dry the aluminum foil at 120 °C for 1 h to obtain a positive electrode plate with a single-sided coated positive electrode active material layer with a thickness of 90 μm and a surface density of 30 mg / cm 2 . Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode plate with a double-sided coated positive electrode active material layer. Then, after cold pressing, slicing, and slitting, dry it under vacuum conditions at 120 °C for 1 h to obtain a positive electrode plate with dimensions of 74 mm (width) × 867 mm (length), and there is a blank foil area of the positive electrode current collector left at one end of the length direction.

[0112] Mix alumina (Dv50 is 2 μm) and binder PVDF in a mass ratio of 80:20. Add N-methylpyrrolidone (NMP) and stir evenly under the action of a vacuum mixer to obtain a positive electrode inorganic coating slurry with a solid content of 30 wt%. Uniformly coat the positive electrode inorganic coating slurry on one surface of the blank foil area of the positive electrode current collector at the tail of the above positive electrode plate (this surface is defined as surface a, and the other surface of the positive electrode current collector is defined as surface b). Dry it at 120 °C for 1 h to obtain a positive electrode plate with a positive electrode inorganic coating on surface a of the positive electrode current collector. The length of the positive electrode inorganic coating is 95 mm and the thickness is 2.5 μm.

[0113] <Preparation of negative electrode plate>

[0114] Mix artificial graphite as the negative electrode active material, conductive agent conductive carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) in a weight ratio of 96.5:1.5:1:1. Add deionized water and stir evenly under the action of a vacuum mixer to obtain a negative electrode slurry, where the solid content of the negative electrode slurry is 75 wt%. Uniformly coat the negative electrode slurry on one surface of a negative electrode current collector copper foil with a thickness of 12 μm. Dry it at 120 °C to obtain a negative electrode plate with a single-sided coated negative electrode material layer with a thickness of 90 μm. Repeat the above steps on the other surface of the negative electrode current collector copper foil to obtain a negative electrode plate with a double-sided coated negative electrode material layer. Then, after cold pressing, slicing, and slitting, obtain a negative electrode plate with specifications of 76 mm (width) × 874 mm (length).

[0115] <Preparation of electrolyte>

[0116] In an argon atmosphere glove box with a water content of less than 10 ppm, first, ethylene carbonate (EC) is heated at a high temperature of 60 °C to be converted into a liquid state. Then, a non-aqueous solvent is prepared by mixing ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a mass ratio of 1:1:1. Subsequently, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate, lithium salt additive lithium tetrafluoroborate, ethylene glycol bis(propionitrile) ether, and 1,2,6-hexanetricarbonitrile are added and mixed evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage content of propyl propionate is 31.000%, the mass percentage content of fluoroethylene carbonate is 8.000%, the mass percentage content of lithium hexafluorophosphate is 12.500%, the mass percentage content A% of lithium salt additive lithium tetrafluoroborate is 0.100%, the mass percentage content B% of ethylene glycol bis(propionitrile) ether is 0.500%, the mass percentage content of 1,2,6-hexanetricarbonitrile is 0.500%, and the balance is the non-aqueous solvent.

[0117] <Preparation of Separator Membrane>

[0118] A polyethylene (PE) microporous membrane with a thickness of 8 μm and a porosity P% of 15% (provided by Shanghai Enjie Co., Ltd.) is used as the base layer of the separator membrane. One surface of the base layer is defined as the c surface, and the other surface is defined as the d surface.

[0119] Preparation of the c-surface coating of the separator membrane:

[0120] Inorganic particles boehmite with a Dv50 of 1.3 μm and polyacrylate (weight average molecular weight of 1.2 million to 2 million) are mixed in a mass ratio of 91:9 and dissolved in deionized water to form an inorganic coating slurry with a solid content of 43 wt%. Subsequently, the inorganic coating slurry is evenly coated on the c surface of the PE base layer by microgravure coating and dried in an oven to obtain a separator membrane with an inorganic coating with a thickness of 1.8 μm on the c surface.

[0121] Add the first polymer polypropylene (PP) particles into a stirrer and stir evenly; add sodium carboxymethyl cellulose into the stirrer and stir evenly; add the wetting agent dimethyl silicone into the stirrer, then add deionized water and stir, add the nitrogen-containing material 2,3-dicyanopyrazine, the binder polyvinylidene fluoride and the inorganic particle boehmite, and adjust the viscosity of the slurry to 45 mPa·s and the solid content to 6 wt% to obtain the second coating slurry. Coat the second coating slurry on the surface of the inorganic coating on the c side of the separator membrane in a stripe distribution manner. The stripe distribution is arranged parallel to the width direction of the separator membrane, and the distance between adjacent second coating stripes is 120 μm. After drying in an oven, a second coating with a thickness of 3 μm is obtained. Among them, the mass ratio of the first polymer, sodium carboxymethyl cellulose, dimethyl silicone, 2,3-dicyanopyrazine, polyvinylidene fluoride and boehmite is 47.5:0.25:2.25:46:3.9:0.1. Based on the total mass of the nitrogen-containing material 2,3-dicyanopyrazine, the binder polyvinylidene fluoride and the inorganic particle boehmite, the mass percentage content M3% of the nitrogen-containing material 2,3-dicyanopyrazine is 92%, the mass percentage content M4% of the binder polyvinylidene fluoride is 7.8%, and the mass percentage content M5% of the inorganic particle boehmite is 0.2%.

[0122] Preparation of the coating on the d side of the separator membrane:

[0123] Mix the inorganic particle boehmite with a Dv50 of 1.3 μm and polyacrylate (weight average molecular weight of 1.2 million to 2 million) according to a mass ratio of 91:9, and dissolve it in deionized water to form an inorganic coating slurry with a solid content of 47 wt%. Subsequently, uniformly coat the inorganic coating slurry on the d side of the PE substrate layer by microgravure coating method, and dry it in an oven to obtain a separator membrane with an inorganic coating with a thickness of 2.2 μm coated on the d side.

[0124] Mix the inorganic particle boehmite and the binder polyvinylidene fluoride according to a mass ratio of M1:M2 = 91:9, then add N-methylpyrrolidone and stir evenly to obtain a binder layer coating solution with a solid content of 7 wt%; coat the binder layer coating solution on the surface of the inorganic coating on the d side of the separator membrane by dip coating method to form a wet film; immerse the separator membrane with the wet film into a coagulation liquid containing deionized water and N-methylpyrrolidone for phase inversion. After immersing for 30 s, put it into an oven and dry it at 60 °C for 2 h to obtain a separator membrane with a binder layer (first coating) with a thickness of 3 μm and an inorganic coating with a thickness of 2.2 μm on the d side, and a second coating with a thickness of 3 μm and an inorganic coating with a thickness of 1.8 μm on the c side. Among them, the mass percentage content of N-methylpyrrolidone in the coagulation liquid is 38%, and the balance is deionized water. The temperatures of the binder layer coating solution and the coagulation liquid are both 25 °C.

[0125] <Preparation of lithium-ion battery>

[0126] Stack the prepared positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play a separating role. Among them, the a side of the positive electrode sheet faces the c side of the separator, wind to obtain an electrode assembly, weld the tabs, then place the electrode assembly in an outer packaging aluminum-plastic film, remove moisture at 80 °C, inject the above electrolyte, and after vacuum packaging, standing, forming (the upper limit voltage of forming is 4.5 V, the forming temperature is 70 °C, and the forming standing time is 2 hours), shaping, capacity testing and other processes, a lithium-ion battery is obtained.

[0127] Examples 1-2 to Examples 1-24

[0128] Except that in <Preparation of electrolyte>, the types and mass percentage contents A% of lithium salt additives and the mass percentage content B% of ethylene glycol bis(propionitrile) ether are adjusted as shown in Table 1, and the mass percentage content of the non-aqueous solvent changes accordingly, while the mass percentage contents of propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate, and 1,2,6-hexanetricarbonitrile remain unchanged. In <Preparation of separator>, except that the porosity P% of the separator base layer is adjusted as shown in Table 1, the rest is the same as Example 1-1.

[0129] Examples 2-1 to Examples 2-5

[0130] Except that in <Preparation of electrolyte>, 4,4'-diphenylether dicarboxylic acid is added according to Table 2, and the mass percentage content C% of 4,4'-diphenylether dicarboxylic acid is adjusted as shown in Table 2, and the mass percentage content of the non-aqueous solvent changes accordingly, while the mass percentage contents of lithium salt additives, ethylene glycol bis(propionitrile) ether, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate, and 1,2,6-hexanetricarbonitrile remain unchanged. The rest is the same as Example 1-1.

[0131] Example 2-6

[0132] Except that in <Preparation of electrolyte>, 4,4'-diphenylether dicarboxylic acid is added according to Table 2, and the mass percentage content C% of 4,4'-diphenylether dicarboxylic acid is adjusted as shown in Table 2, and the mass percentage content of the non-aqueous solvent changes accordingly, while the mass percentage contents of lithium salt additives, ethylene glycol bis(propionitrile) ether, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate, and 1,2,6-hexanetricarbonitrile remain unchanged. The rest is the same as Example 1-21.

[0133] Examples 3-1 to Examples 3-6

[0134] Except that in the <Preparation of electrolyte>, methylene methanedisulfonate is added according to Table 3, and the mass percentage content D% of methylene methanedisulfonate is adjusted as shown in Table 3, the mass percentage content of the non-aqueous solvent changes accordingly, and the mass percentage contents of the lithium salt additive, ethylene glycol bis(propionitrile) ether, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate and 1,2,6-hexanetricarbonitrile remain unchanged. Otherwise, it is the same as Example 1-1.

[0135] Example 3-7

[0136] Except that in the <Preparation of electrolyte>, methylene methanedisulfonate is added according to Table 3, and the mass percentage content D% of methylene methanedisulfonate is adjusted as shown in Table 3, the mass percentage content of the non-aqueous solvent changes accordingly, and the mass percentage contents of the lithium salt additive, ethylene glycol bis(propionitrile) ether, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate and 1,2,6-hexanetricarbonitrile remain unchanged. Otherwise, it is the same as Example 1-21.

[0137] Examples 4-1 to 4-6

[0138] Except that in the <Preparation of separator>, the preparation parameters of the adhesive layer on the d side of the separator are adjusted according to Table 4, so that the average wall thickness T nm between adjacent pores in the adhesive layer is as shown in Table 4. Otherwise, it is the same as Example 1-1.

[0139] Examples 5-1 to 5-6

[0140] Except that in the <Preparation of separator>, the preparation parameters of the second coating on the c side of the separator are adjusted according to Table 5, so that the ratio Y of the apparent concentration of nitrogen element to the apparent concentration of carbon element in the area of 2μm×2μm on the surface of the second coating is as shown in Table 5. Otherwise, it is the same as Example 1-1.

[0141] Examples 6-1 to 6-10

[0142] Except that in the <Preparation of positive electrode sheet>, the average particle size Fμm and specific surface area Sm of the positive electrode active material are adjusted according to Table 6 2 / g. Otherwise, it is the same as Example 1-1.

[0143] Example 6-11

[0144] Except that in the <Preparation of positive electrode sheet>, the positive electrode active material is not coated with Al2O3. Otherwise, it is the same as Example 1-1. The <Preparation of positive electrode sheet> is as follows:

[0145] The positive electrode active material lithium cobalt oxide LiCoO2 (specific surface area Sm 2 / g is 0.2m 2 / g, with an average particle size F μm of 20 μm), conductive agent conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 97:1:2. N-methylpyrrolidone (NMP) was added, and 2800 ppm of methyl acrylate, an additive containing acrylate, was added. The mixture was stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 65 wt%. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm and a surface tension value E dyn / cm of 26 dyn / cm. The aluminum foil was dried at 120 °C for 1 h to obtain a positive electrode plate with a single-sided coating of a positive electrode active material layer with a thickness of 90 μm and a surface density of 30 mg / cm 2 The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode plate with a double-sided coating of the positive electrode active material layer. Then, after cold pressing, slicing, and slitting, it was dried under vacuum conditions at 120 °C for 1 h to obtain a positive electrode plate with a size specification of 74 mm (width) × 867 mm (length), and there was a blank foil area of the positive electrode current collector left at one end of the length direction.

[0146] Aluminum oxide (Dv50 is 2 μm) and binder PVDF were mixed at a mass ratio of 80:20. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under the action of a vacuum mixer to obtain a positive electrode inorganic coating slurry with a solid content of 30 wt%. The positive electrode inorganic coating slurry was evenly coated on one surface (this surface is defined as the a surface, and the other surface of the positive electrode current collector is defined as the b surface) of the blank foil area of the positive electrode current collector at the tail of the above positive electrode plate. It was dried at 120 °C for 1 h to obtain a positive electrode plate with a positive electrode inorganic coating on the a surface of the positive electrode current collector. The length of the positive electrode inorganic coating is 95 mm, and the thickness is 2.5 μm.

[0147] Comparative Examples 1-1 to Comparative Examples 1-8

[0148] Except that in <Preparation of Electrolyte>, the mass percentage content B% of ethylene glycol bis(propionitrile) ether was adjusted as shown in Table 1, and the mass percentage content of the non-aqueous solvent changed accordingly, while the mass percentage contents of the lithium salt additive, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate, and 1,2,6-hexanetricarbonitrile remained unchanged. In <Preparation of Separator>, except that the porosity P% of the separator substrate layer was adjusted as shown in Table 1, the rest was the same as in Example 1-1.

[0149] Table 1

[0150]

[0151] Table 2

[0152]

[0153] Note: " / " in Table 2 indicates no corresponding preparation parameters.

[0154] Table 3

[0155]

[0156] Note: " / " in Table 3 indicates no corresponding preparation parameters.

[0157] Table 4

[0158]

[0159] Table 5

[0160]

[0161] Table 6

[0162]

[0163] It can be seen from Examples 1-1 to 1-24 and Comparative Examples 1-1 to 1-8 that when the electrolyte includes a lithium salt additive and ethylene glycol bis(propionitrile) ether, adopting the types of lithium salt additives in the present application and regulating the value of A within the scope of the present application, and regulating the content ratio A / B of the lithium salt additive and ethylene glycol bis(propionitrile) ether within the scope of the present application, and matching with a separator having a porosity P value of the substrate layer within the scope of the present application, the prepared lithium-ion battery has a high low-temperature floating charge capacity retention rate, a high passing rate in the hot box test, and a high passing rate in the overcharge test, indicating that the lithium-ion battery has good low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure.

[0164] The value of the content C of 4,4'-diphenylether dicarboxylic acid usually affects the low-temperature floating charge performance, safety performance, and overcharge resistance performance of lithium-ion batteries under high temperature and high pressure. It can be seen from Examples 1-1, 2-1 to 2-5, and 1-21, 2-6 that when the value of C is regulated within the scope of the present application, the prepared lithium-ion battery has a high low-temperature floating charge capacity retention rate, a high passing rate in the hot box test, and a high passing rate in the overcharge test, indicating that the lithium-ion battery has good low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure.

[0165] The value of the content D of methylene methanesulfonate usually affects the low-temperature floating charge performance, safety performance, and overcharge resistance performance of lithium-ion batteries under high temperature and high pressure. It can be seen from Examples 1-1, 3-1 to 3-6, and 1-21, 3-7 that when the value of D is regulated within the scope of the present application, the prepared lithium-ion battery has a high low-temperature floating charge capacity retention rate, a high passing rate in the hot box test, and a high passing rate in the overcharge test, indicating that the lithium-ion battery has good low-temperature floating charge performance, safety performance, and overcharge resistance performance under high temperature and high pressure.

[0166] The value of the average wall thickness T between adjacent holes in the separator bonding layer generally affects the low-temperature floating charge performance, safety performance, overcharge resistance performance under high temperature and high pressure, and low-temperature rate performance of lithium-ion batteries. It can be seen from Example 1-1, Examples 4-1 to 4-6 that when the value of T is adjusted within the scope of this application, the prepared lithium-ion battery has a high low-temperature floating charge capacity retention rate, a high heat box test passing rate, a high overcharge test passing rate, a good lithium plating situation, and a high -10°C 1C low-temperature retention rate, indicating that the lithium-ion battery has good low-temperature floating charge performance, safety performance, overcharge resistance performance under high temperature and high pressure, and low-temperature rate performance.

[0167] The value of the ratio Y of the apparent concentration of nitrogen element to the apparent concentration of carbon element on the surface of the second coating of the separator generally affects the low-temperature floating charge performance, safety performance, overcharge resistance performance under high temperature and high pressure, and low-temperature discharge performance of lithium-ion batteries. It can be seen from Example 1-1, Examples 5-1 to 5-6 that when the value of Y is adjusted within the scope of this application, the prepared lithium-ion battery has a high low-temperature floating charge capacity retention rate, a high heat box test passing rate, a high overcharge test passing rate, a low gas generation amount, a low low-temperature voltage drop, and a high drop test passing rate, indicating that the lithium-ion battery has good low-temperature floating charge performance, safety performance, overcharge resistance performance under high temperature and high pressure, and low-temperature discharge performance.

[0168] The ratio E / F of the dyne value E of the positive current collector to the average particle size F of the positive active material, the specific surface area S of the positive active material, and the value of the average particle size F of the positive active material generally affect the low-temperature floating charge performance, safety performance, overcharge resistance performance under high temperature and high pressure, low-temperature discharge performance, and low-temperature rate performance of lithium-ion batteries. It can be seen from Example 1-1, Examples 6-1 to 6-10 that when the values of E / F, S, and F are adjusted within the scope of this application, the prepared lithium-ion battery has a high low-temperature floating charge capacity retention rate, a high heat box test passing rate, a high overcharge test passing rate, a low gas generation amount, a low low-temperature voltage drop, a high drop test passing rate, and a high -10°C 1C low-temperature retention rate, indicating that the lithium-ion battery has good low-temperature floating charge performance, safety performance, overcharge resistance performance under high temperature and high pressure, low-temperature discharge performance, and low-temperature rate performance.

[0169] The presence of aluminum in the positive electrode active material generally affects the low-temperature floating charge performance, safety performance, overcharge resistance performance under high temperature and high pressure, low-temperature discharge performance, and low-temperature rate performance of lithium-ion batteries. As can be seen from Examples 1-1 and 6-11, lithium-ion batteries with aluminum in the positive electrode active material have a higher low-temperature floating charge capacity retention rate, a higher passing rate in the hot box test, a higher passing rate in the overcharge test, a lower gas generation amount, a lower low-temperature voltage drop, a higher passing rate in the drop test, and a higher -10°C 1C low-temperature retention rate, indicating that the lithium-ion batteries have good low-temperature floating charge performance, safety performance, overcharge resistance performance under high temperature and high pressure, low-temperature discharge performance, and low-temperature rate performance.

[0170] It should be noted that, in this article, relational terms such as first and second are only used 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 term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method or article.

[0171] The term "one of", "a", "a kind of" or other similar terms connecting elements refers to any one of the listed elements. For example, "one of A or B" means only A or only B; for another example, "one of A, B and C" means only A, only B or only C. The term "at least one of", "at least a", "at least a kind of" or other similar terms connecting elements refers to any combination of the listed elements. For example, "at least one of A or B" means only A, only B, A and B. For another example, "at least one of A, B or C" means only A, only B, only C, only A and B, only A and C, only B and C, A and B and C.

[0172] Each embodiment in this specification is described in a related manner. The same or similar parts between each embodiment can be referred to each other, and the differences between each embodiment and other embodiments are emphasized.

[0173] The above are only the preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, wherein, The secondary battery includes an electrolyte and a separator. The electrolyte includes a lithium salt additive and ethylene glycol bis(propionitrile) ether. Based on the total mass of the electrolyte, the mass percentage of the lithium salt additive is A%, and the mass percentage of the ethylene glycol bis(propionitrile) ether is B%, where 0.035 ≤ A / B ≤ 20 and 0.005 ≤ B ≤ 2.

9. The lithium salt additive satisfies at least one of the following characteristics: a. The lithium salt additive includes lithium bis(fluorosulfonyl)imide, where 0.1 ≤ A ≤ 2.5; b. The lithium salt additive includes lithium tetrafluoroborate, where 0.1 ≤ A ≤ 2.5; The separator includes a substrate layer, and the porosity of the substrate layer is P%, where 15 ≤ P ≤ 35.

2. The secondary battery according to claim 1, wherein, 0.047 ≤ A / B ≤ 10.

3. The secondary battery according to claim 1, wherein 0.047 ≤ A / B ≤ 5.

4. The secondary battery according to claim 1, wherein, 15≤P≤25。 5. The secondary battery according to claim 1, wherein The electrolyte further includes 4,4'-diphenylether dicarboxylic acid. Based on the total mass of the electrolyte, the mass percentage of the 4,4'-diphenylether dicarboxylic acid is C%, where 0.5 ≤ C ≤ 2.

5.

6. The secondary battery according to claim 1, wherein, The electrolyte further includes methylene methanedisulfonate. Based on the total mass of the electrolyte, the mass percentage of the methylene methanedisulfonate is D%, where 0.01 ≤ D ≤ 0.

5.

7. The secondary battery according to any one of claims 1 to 6, wherein, The separator further includes a first coating on at least one surface of the substrate layer. The first coating includes an adhesive layer, and the average wall thickness between adjacent pores in the adhesive layer is T nm, where 2 ≤ T ≤ 450.

8. The secondary battery according to any one of claims 1 to 6, wherein, The separator further includes a second coating on at least one surface of the substrate layer. On the surface of the second coating, in a region of 2 μm × 2 μm, the ratio of the apparent concentration of nitrogen element to the apparent concentration of carbon element is Y, where 1 ≤ Y ≤ 8.

9. The secondary battery according to claim 8, wherein, 1≤Y≤4。 10. The secondary battery according to any one of claims 1 to 6, wherein, The secondary battery further includes a positive electrode plate, which includes a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector. The dyne value of the positive electrode current collector is E dyn / cm, and the positive electrode active material layer includes a positive electrode active material. The average particle size of the positive electrode active material is F μm, where 0.5 ≤ E / F ≤ 30.

11. The secondary battery according to claim 10, wherein, 1 ≤ E / F ≤ 12.

5.

12. The secondary battery according to claim 10, wherein, The specific surface area of the positive electrode active material is Sm 2 / g, 0.05 ≤ S ≤ 0.

86.

13. The secondary battery according to claim 10, wherein, The positive electrode active material contains aluminum element.

14. The secondary battery according to claim 10, wherein 1≤F≤30。 15. An electronic device, wherein, The electronic device includes the secondary battery according to any one of claims 1 to 14.

Images