Secondary battery and electronic device

Abstract

The present application provides a secondary battery and an electronic device, wherein the secondary battery comprises an electrolyte and an isolating membrane, wherein the electrolyte comprises a lithium salt additive and ethylene glycol bis(propionitrile) ether, wherein the mass percentage of the lithium salt additive is A%, the mass percentage of the ethylene glycol bis(propionitrile) ether is B%, and 0.035≤A / B≤20 based on the total mass of the electrolyte; the lithium salt additive satisfies at least one of the following characteristics: a. the lithium salt additive comprises lithium bis(fluorosulfonyl)imide, 0.1≤A≤2.5; b. the lithium salt additive comprises lithium tetrafluoroborate, 0.1≤A≤2.5; the isolating membrane comprises a substrate layer, and the porosity of the substrate layer is P%, and 15≤P≤35. The present application adopts the electrolyte and the isolating membrane, and regulates the values ​​of A / B, A, and P within the scope of the present application, so that the secondary battery of the present application can have good low-temperature floating charging performance, safety performance, and anti-overcharging performance under high temperature and high pressure.

Description

Technical Field

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

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in smart phones, wearable devices, consumer drones, electric vehicles and other fields due to their high energy density, long cycle life and no memory effect. With the widespread application of lithium-ion batteries in the above fields, the market has higher and higher performance requirements for lithium-ion batteries. However, during the cycle of existing lithium-ion batteries, there are many side reactions between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, which will affect the low-temperature floating performance, safety performance and anti-overcharge performance of lithium-ion batteries under high temperature and high pressure. Summary of the invention

[0003] 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 anti-overcharge performance of the secondary battery under high temperature and high pressure. The specific technical solution is as follows:

[0004] A first aspect of the present application provides a secondary battery, wherein the secondary battery comprises an electrolyte and an isolation 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 of the lithium salt additive is A%, the mass percentage of the ethylene glycol bis(propionitrile) ether is B%, and 0.035≤A / B≤20; the lithium salt additive satisfies at least one of the following characteristics: a. the lithium salt additive comprises lithium bis(fluorosulfonyl)imide, 0.1≤A≤2.5; b. the lithium salt additive comprises lithium tetrafluoroborate, 0.1≤A≤2.5; the isolation membrane comprises a substrate layer, and the porosity of the substrate layer is P%, and 15≤P≤35. 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 positive electrode 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 the present application, the CEI film can have good mechanical strength and chemical stability, good density and uniformity, and can inhibit the formation of electrolyte side reactions and reduce the generation of interfacial gas. At the same time, by regulating the porosity of the isolation membrane substrate layer within the scope of the present application, the CEI membrane and the isolation membrane at the interface can have adaptive ion permeability and electronic insulation, so that the secondary battery of the present application has good low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure.

[0005] 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 membrane formed by the lithium salt additive and ethylene glycol bis(propionitrile) ether can be further improved, so that the ion permeability and electronic insulation of the CEI membrane are more suitable, thereby further improving the low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure of the secondary battery.

[0006] 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 membrane formed by the lithium salt additive and ethylene glycol bis(propionitrile) ether can be further improved, so that the ion permeability and electronic insulation of the CEI membrane are better adapted, thereby further improving the low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure of the secondary battery.

[0007] In some embodiments, 15≤P≤25. By regulating the value of P within the above range, the CEI membrane and the isolation membrane can have better electronic insulation and ion permeability, and the isolation membrane itself meets certain structural strength and stability. At the same time, the use of the electrolyte in the present application can reduce the risk of isolation membrane deformation, thereby improving the low-temperature floating performance, safety performance and anti-overcharge performance of the secondary battery under high temperature and high pressure.

[0008] In some embodiments, the electrolyte further includes 4,4'-diphenyl ether dicarboxylic acid, and the mass percentage of 4,4'-diphenyl ether dicarboxylic acid is C%, 0.5≤C≤2.5 based on the total mass of the electrolyte. By using an electrolyte further including 4,4'-diphenyl ether dicarboxylic acid and adjusting the value of C within the above range, 4,4'-diphenyl ether dicarboxylic acid can form a more stable, more uniform and thinner CEI film with lithium salt additives and ethylene glycol bis(propionitrile) ether, and can also form a stable and thinner negative electrode solid electrolyte interface film (SEI film) at the interface between the negative electrode plate and the electrolyte, and can make the formed SEI film and CEI film have good electronic insulation and ion permeability, so as to improve the low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure of the secondary battery.

[0009] In some embodiments, the electrolyte further includes methylene disulfonate, and the mass percentage of methylene disulfonate is D%, based on the total mass of the electrolyte, and 0.01≤D≤0.5. By using an electrolyte further including methylene disulfonate and adjusting the value of D within the above range, methylene disulfonate can form a more stable, more uniform and thinner CEI film with lithium salt additives and ethylene glycol bis(propionitrile) ether, and can make the formed SEI film have better electronic insulation and ion permeability, thereby improving the low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure of the secondary battery.

[0010] In some embodiments, the isolation film also includes a first coating located on at least one surface of the substrate layer, the first coating includes an adhesive layer, and the average wall thickness between adjacent holes in the adhesive layer is T nm, 2≤T≤450. When the average wall thickness between adjacent holes in the adhesive layer is within the range of the present application, the isolation film can be bonded to the pole piece with good uniformity, reducing the risk of pole piece detachment caused by large differences in bonding strength in local areas, thereby reducing the phenomenon of lithium precipitation and black spots in some areas caused by the difference in local rates of lithium ion transmission, so that the secondary battery of the present application has good low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, while also having good low-temperature rate performance and safety performance. At the same time, the average wall thickness between adjacent holes in the adhesive layer is within the above range, so that the strength of the isolation film is relatively uniform, which can make the secondary battery have a higher pass rate in the safety test, so that the secondary battery has better safety performance.

[0011] In some embodiments, the isolation film further comprises a second coating located on at least one surface of the substrate layer, and the surface of the second coating has a ratio of the apparent concentration of nitrogen element to the apparent concentration of carbon element of Y in an area of ​​2 μm×2 μm, 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 isolation film is within the scope of the present application, the isolation film has a functional group containing N element, which can play a stable binding role with the metal ions of the positive electrode active material, reduce the binding energy, and make the isolation film and the positive electrode plate structure more stable, so that the secondary battery can have a higher pass rate in the safety test, and at the same time can reduce the gas production and self-discharge of the secondary battery during the cycle process, reduce the voltage drop, so that the secondary battery has good low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, and also has good low-temperature discharge performance and safety performance.

[0012] In some embodiments, 1≤Y≤4. By regulating 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 of the isolation membrane can better and more stably bind to the metal ions on the positive active material, further reducing the binding energy, thereby making the isolation membrane and the positive electrode sheet structure more stable, so that the secondary battery has a higher pass rate in the safety test, and can further reduce the gas production and self-discharge of the secondary battery during the cycle process, reduce the voltage drop, so that the secondary battery has better low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, and also has better low-temperature discharge performance and safety performance.

[0013] In some embodiments, the secondary battery further comprises a positive electrode sheet, the positive electrode sheet comprises a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector, the dyne value of the positive current collector is Edyn / cm, the positive electrode material layer comprises a positive active material, the average particle size of the positive active material is F μm, and 0.5≤E / F≤30. The present application regulates the ratio E / F of the dyne value of the positive current collector and the average particle size of the positive active material within the scope of the present application, the surface tension of the positive current collector itself is adapted to the positive active material particles used, so that the force between the two is appropriate, the positive electrode sheet can have a higher strength, and when the electrolyte of the present application is used, it can maintain a good structural stability, so that the secondary battery can have a higher pass rate in the safety test, and at the same time can reduce the gas production of the secondary battery during the cycle process, reduce the voltage drop, so that the secondary battery has good low-temperature floating performance and anti-overcharge performance under high temperature and high pressure, and also has good low-temperature discharge performance and safety performance.

[0014] In some embodiments, 1≤E / F≤12.5. When the ratio E / F of the positive electrode current collector dyne value and the average particle size of the positive electrode active material is within the above range, the positive electrode sheet can have a higher strength, and can maintain better structural stability when the electrolyte of the present application is used, so that the secondary battery has better low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, and also has better low-temperature discharge performance and safety performance.

[0015] In some embodiments, the specific surface area of ​​the positive electrode active material is S m 2 / g, 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 sheet, and can make the secondary battery have a higher pass rate in the safety test, while being able to 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 anti-overcharge performance under high temperature and high pressure, and also has good low-temperature discharge performance, low-temperature rate performance and safety performance.

[0016] In some embodiments, the positive electrode active material contains aluminum. The positive electrode active material contains aluminum, which participates in the formation of the interface CEI film, can increase the Young's modulus of the interface CEI film, improve the strength and hardness of the CEI film, reduce the impact 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 anti-overcharge performance under high temperature and high pressure, and also has good low-temperature discharge performance, low-temperature rate performance and safety performance.

[0017] 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 fit under a certain modulus of the positive electrode current collector, further improves the stability of the positive electrode pole piece, and enables the secondary battery to have a higher pass rate in the safety test, while further reducing the voltage drop of the secondary battery, further improving the low-temperature rate performance of the secondary battery, so that the secondary battery has better low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, and also has better low-temperature discharge performance, low-temperature rate performance and safety performance.

[0018] A 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.

[0019] The present application provides a secondary battery and an electronic device. The secondary battery includes an electrolyte and an isolation membrane. 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%, the mass percentage of the ethylene glycol bis(propionitrile) ether is B%, and 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 isolation membrane includes a substrate layer, and the porosity of the substrate layer is P%, 15≤P≤35. The present application adopts 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 lithium salt additive is solvated, and a 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 the present application, the CEI film can have good mechanical strength and chemical stability, good density and uniformity, and can inhibit the formation of electrolyte side reactions and reduce the generation of interfacial gas. At the same time, by regulating the porosity of the isolation membrane substrate layer within the scope of the present application, the CEI film and the isolation membrane at the interface can have adaptive ion permeability and electronic insulation, so that the secondary battery of the present application has good low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure.

[0020] Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the present application. Obviously, the described embodiments are only 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.

[0022] In a first aspect, the present application provides a secondary battery, wherein the secondary battery includes an electrolyte and an isolation membrane, 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%, the mass percentage of the ethylene glycol bis(propionitrile) ether is B%, and 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 isolation membrane includes a substrate layer, and the porosity of the substrate layer is P%, 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 consisting of any two of them; 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 consisting of any two of them; P can be 15, 17, 19, 20, 22, 24, 25, 26, 28, 30, 31, 32, 33, 34, 35, or a range consisting of any two of them. In the present application, the above-mentioned substrate layers with different porosities can be purchased, and then tested in combination with the test methods of the above-mentioned parameters provided below in the present application to select the desired substrate layer.

[0023] When the value of A / B is too small, for example, less than 0.035, the content of lithium salt additive is low, it is difficult to form a CEI membrane with good mechanical strength and chemical stability, the effect of inhibiting the formation of electrolyte side reactions is poor, and it is difficult to improve the low-temperature floating performance, safety performance and anti-overcharge performance of the secondary battery under high temperature and high pressure. When the value of A / B is too large, for example, greater than 20, the content of lithium salt additive is too high, which will make the stability of the CEI membrane worse, the effect of inhibiting the occurrence of electrolyte side reactions is worse, and the density of the CEI membrane is too high, which affects the transmission of lithium ions and leads to an increase in by-products, which is not conducive to improving the low-temperature floating performance, safety performance and anti-overcharge performance of the secondary battery under high temperature and high pressure. When the value of P is too small, for example, less than 15, the pores on the substrate layer of the isolation membrane are small, and the ion permeability is poor, which is not conducive to improving the low-temperature floating performance and anti-overcharge performance of the secondary battery under high temperature and high pressure. When the value of P is too large, for example, greater than 35, the pores on the substrate layer of the isolation membrane are too many, which will increase the risk of internal short circuit of the secondary battery, which 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 plate and the electrolyte. By regulating 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, good density and uniformity, and can inhibit the formation of electrolyte side reactions and reduce the generation of interfacial gas. At the same time, by regulating the porosity of the isolation membrane substrate layer within the scope of the present application, the CEI film and the isolation membrane at the interface can have adaptive ion permeability and electronic insulation, so that the secondary battery of the present application has good low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure.

[0024] In some embodiments, it is further preferred that 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 membrane formed by the lithium salt additive and ethylene glycol bis(propionitrile) ether can be further improved, so that the ion permeability and electronic insulation of the CEI membrane are more suitable, thereby further improving the low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure of the secondary battery.

[0025] In some embodiments, it is further preferred that 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 membrane formed by the lithium salt additive and ethylene glycol bis(propionitrile) ether can be further improved, so that the ion permeability and electronic insulation of the CEI membrane are better adapted, thereby further improving the low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure of the secondary battery.

[0026] In some embodiments, it is further preferred that 15≤P≤25. By regulating the value of P within the above range, the CEI membrane and the isolation membrane can have better electronic insulation and ion permeability, and the isolation membrane itself meets certain structural strength and stability. At the same time, the use of the electrolyte in the present application can reduce the risk of isolation membrane deformation, thereby improving the low-temperature floating performance, safety performance and anti-overcharge performance of the secondary battery under high temperature and high pressure.

[0027] In some embodiments, the lithium salt additive includes lithium bis(fluorosulfonyl)imide (LiFSI), 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 density and thinness under high pressure, thereby improving the low-temperature floating charge performance, safety performance and anti-overcharge performance of the secondary battery under high temperature and high pressure.

[0028] 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 density and thinness under high pressure, thereby improving the low-temperature floating charge performance, safety performance and anti-overcharge performance of the secondary battery under high temperature and high pressure.

[0029] In some embodiments, the lithium salt additive includes lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate, 0.1≤A≤2.5. In some embodiments, the mass ratio of lithium bis(fluorosulfonyl)imide and 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 adjusted 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 suitable density and thinner 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, while having better anti-overcharge performance under high temperature and high pressure.

[0030] 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 consisting of any two of these values. Regulating the value of B within the above range is beneficial to the chelation 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 density and relatively thinness, thereby improving the low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure of the secondary battery.

[0031] In some embodiments, the electrolyte further includes 4,4'-diphenyl ether dicarboxylic acid, and the mass percentage of 4,4'-diphenyl ether dicarboxylic acid is C%, 0.5≤C≤2.5 based on the total mass of the electrolyte. For example, C can be 0.5, 1.0, 1.2, 1.5, 1.7, 2.0, 2.2, 2.5 or a range consisting of any two values ​​therein. By using an electrolyte further including 4,4'-diphenyl ether dicarboxylic acid and adjusting the value of C within the above range, 4,4'-diphenyl ether dicarboxylic acid can form a more stable, more uniform and thinner CEI film with a lithium salt additive and ethylene glycol bis(propionitrile) ether, and at the same time can form a stable and thinner negative electrode solid electrolyte interface film (SEI film) at the interface between the negative electrode plate and the electrolyte, and can make the formed SEI film and CEI film have good electronic insulation and ion permeability, thereby improving the low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure of the secondary battery.

[0032] In some embodiments, the electrolyte further comprises methylene disulfonate, and the mass percentage of methylene disulfonate based on the total mass of the electrolyte is D%, and 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 consisting of any two of the values. By using an electrolyte that also includes methylene disulfonate and regulating the value of D within the above range, methylene disulfonate can form a more stable, more uniform and thinner CEI film with the lithium salt additive and ethylene glycol bis(propionitrile) ether, and can make the formed SEI film have better electronic insulation and ion permeability, thereby helping to improve the low-temperature floating charge performance, safety performance and anti-overcharge performance of the secondary battery under high temperature and high pressure.

[0033] In some embodiments, the electrolyte further comprises 4-isopropylphenyl diphenyl phosphate, and the mass percentage of 4-isopropylphenyl diphenyl phosphate is G%, based on the total mass of the electrolyte, and 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 consisting of any two of the values. By using an electrolyte that also includes 4-isopropylphenyl diphenyl phosphate and regulating 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 plate and the electrolyte, can inhibit solvent decomposition of the electrolyte during the reduction process, and can reduce the risk of lithium dendrites deposited on the surface of the negative electrode plate, thereby improving the low-temperature floating charge performance of the secondary battery and the anti-overcharge performance under high temperature and high pressure, while also improving the high-temperature storage performance and low-temperature intermittent cycle performance of the secondary battery, and can further improve the safety performance of the secondary battery.

[0034] In some embodiments, the electrolyte further includes other additives, including at least one of vinyl sulfate (DTD), vinylene sulfate (VC) or 1,3-propane sultone; further, the other additives also include at least one of fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, trifluoroethyl methyl carbonate or bis(trifluoroethyl) carbonate. The present application does not particularly limit the content of other additives, as long as the purpose of the present application can be achieved, for example, based on the total mass of the electrolyte, the mass percentage of other additives is 0.2% to 2.5%.

[0035] In some embodiments, in addition to the above-mentioned lithium salt additives, the electrolyte also includes other ionizable lithium salts, including LiPF 6 、LiSbF 6 、LiAsF 6 、LiClO 4 、LiN(C 2 F 5 SO 2 ) 2 CF 3 SO 3 Li、LiC(CF 3 SO 2 ) 3 or LiC 4 BO 8At least one of. The present application has no particular limitation on the content of other ionizable lithium salts, as long as the purpose of the present application can be achieved. In some embodiments, based on the total mass of the electrolyte, the mass percentage of other ionizable lithium salts is 8% to 15%, preferably 8% to 12%, and more preferably 8% to 10%. Controlling the content of other ionizable lithium salts within the above range can make the electrolyte have a suitable number of mobile lithium ions, make the viscosity of the electrolyte within a suitable range, improve the migration rate of lithium ions, and enhance the performance of the secondary battery.

[0036] In some embodiments, the electrolyte further includes propyl propionate, and the content of propyl propionate is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage of propyl propionate is 22% to 40%. In some embodiments, the electrolyte further includes fluoroethylene carbonate (FEC), and the content of fluoroethylene carbonate is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage of fluoroethylene carbonate is 0.5% to 10%. In some embodiments, the electrolyte further includes a trinitrile compound, and the content of the trinitrile compound is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage of the trinitrile compound is 0.1% to 5%. In some embodiments, the trinitrile compound includes at least one of 1,2,6-hexane trinitrile, 1,3,6-hexane trinitrile, or 1,3,5-pentane trinitrile.

[0037] In some embodiments, the electrolyte further comprises fluoroether. The present application has no particular limitation on the content of fluoroether, as long as the purpose of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage of fluoroether is 0.5% to 4.5%.

[0038] In some embodiments, the electrolyte further includes a non-aqueous solvent. The present application has no particular limitation on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.

[0039] The carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The chain carbonate compound may include but is 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 cyclic carbonate compound may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is 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 trifluoromethylethylene carbonate. The carboxylate compound may include, but is not limited to, at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolactone, valerolactone, mevalonolactone, caprolactone, or methyl formate. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 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, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application has no particular restrictions on the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage of the non-aqueous solvent is 48% to 69%, for example, the mass percentage 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 consisting of any two of these values.

[0040] In some embodiments, the isolation film further comprises a first coating layer located on at least one surface of the substrate layer, the first coating layer comprises a bonding layer, and the average wall thickness between adjacent holes in the bonding layer is T nm, 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 consisting of any two of the values. If the average wall thickness between adjacent holes in the bonding layer of the isolation film is too low, for example, less than 2 nm, it is difficult to achieve in terms of technology. When the average wall thickness between adjacent holes in the bonding layer is within the range of this application, the bonding uniformity between the isolation membrane and the pole piece can be improved, reducing the risk of pole piece detachment caused by large differences in bonding strength in local areas, thereby reducing the phenomenon of lithium precipitation and black spots in some areas caused by the difference in local lithium ion transmission rate, so that the secondary battery of this application has good low-temperature floating performance and anti-overcharge performance under high temperature and high pressure, as well as good low-temperature rate performance and safety performance. At the same time, the average wall thickness between adjacent holes in the bonding layer is within the above range, so that the strength of the isolation membrane is more uniform, which can make the secondary battery have a higher pass rate in the safety test, so that the secondary battery has better safety performance.

[0041] In some embodiments, the isolation film further comprises a second coating located on at least one surface of the substrate layer, and the surface of the second coating has a ratio of the apparent concentration of nitrogen to the apparent concentration of carbon in an area of ​​2 μm×2 μm, 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 consisting of any two of these values. When the ratio Y of the apparent concentration of nitrogen to the apparent concentration of carbon on the surface of the second coating of the isolation film is within the scope of the present application, the isolation film has a functional group containing N element, which can play a stable binding role with the metal ions of the positive active material, reduce the binding energy, and make the isolation film and the positive electrode plate structure more stable, so that the secondary battery can have a higher pass rate in the safety test, and at the same time can reduce the gas production and self-discharge of the secondary battery during the cycle process, reduce the voltage drop, so that the secondary battery has good low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, and also has good low-temperature discharge performance and safety performance.

[0042] In some embodiments, 1≤Y≤4. By regulating 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 of the isolation membrane can better and more stably bind to the metal ions on the positive active material, further reducing the binding energy, thereby making the isolation membrane and the positive electrode sheet structure more stable, so that the secondary battery has a higher pass rate in the safety test, and can further reduce the gas production and self-discharge of the secondary battery during the cycle process, reduce the voltage drop, so that the secondary battery has better low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, and also has better low-temperature discharge performance and safety performance.

[0043] In some embodiments, the substrate layer of the isolation film 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 substrate layer of the isolation film includes at least one of polyethylene or polypropylene, which has a good effect on preventing short circuits and can improve the safety performance of secondary batteries through the shutdown effect. The molecular weight of the substrate layer is not particularly limited in this application, as long as the purpose of this application can be achieved.

[0044] In some embodiments, the isolation film further comprises an inorganic coating, which is disposed on at least one surface of the isolation film. In some embodiments, the isolation film further comprises an inorganic coating, which is disposed between the substrate layer and the first coating along the thickness direction of the isolation film. In some embodiments, the isolation film further comprises an inorganic coating, which is disposed between the substrate layer and the second coating along the thickness direction of the isolation film. The inorganic coating comprises inorganic particles and a binder, and the inorganic particles are selected from aluminum oxide (Al 2 O 3 ), silicon oxide (SiO 2 )、MgO、TiO 2 )、HfO 2 )、Tin Oxide(SnO 2 ), cerium dioxide (CeO 2 )、nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular limitation on the binder, as long as the purpose 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, polyacrylic acid salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene. The isolation membrane with an inorganic coating can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the pole piece. The present application has no particular limitation on the mass ratio of inorganic particles to binder, as long as the purpose of the present application can be achieved.

[0045] In some embodiments, the bonding layer includes inorganic particles and a binder, the binder includes a high temperature resistant resin, and the high temperature resistant resin includes at least one of a high melting point crystalline polymer or a high temperature resistant amorphous polymer. The high melting point crystalline polymer includes at least one of polypropylene, poly-4-methylpentene, polytetrafluoroethylene or polyvinylidene fluoride, and the high temperature resistant amorphous polymer includes 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 a range consisting of any two of the values. Using a separator including a bonding layer of the above-mentioned high temperature resistant resin, and regulating the mass percentage of the high temperature resistant resin within the above-mentioned range, is conducive to improving the melting temperature and strength of the separator, and is conducive to improving the high temperature performance of the secondary battery. The present application has no particular restrictions on the inorganic particles, as long as the purpose of the present application can be achieved, for example, the inorganic particles can be at least one of the above-mentioned inorganic particles.

[0046] In some embodiments, the step of preparing the bonding layer includes: mixing the inorganic particles and the binder according to a mass ratio, then adding the first solvent and stirring evenly to obtain a bonding layer coating liquid with a solid content of 3-14wt%, coating it on the surface of the isolation film, immersing it in the coagulation liquid for 15s to 100s, and then drying it at a temperature of 20°C to 100°C for 0.5h to 6h to obtain an isolation film with a bonding layer. The present application has no special restrictions on the first solvent, as long as the purpose of the present application can be achieved, for example, the first solvent is N-methylpyrrolidone. The present application has no special restrictions on the coagulation liquid, as long as the purpose of the present application can be achieved, for example, the coagulation liquid includes 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. The present application has no special restrictions on the types of the second solvent and the third solvent, as long as the purpose of the present application can be achieved, for example, the second solvent is N-methylpyrrolidone, and the third solvent is deionized water. In the present application, the average wall thickness T nm between adjacent holes in the bonding layer can be controlled by adjusting the mass ratio of inorganic particles and binder in the bonding layer preparation step, the solid content of the bonding layer coating solution and other parameters. Specifically, increasing the mass ratio of inorganic particles and binder in the bonding layer will reduce T; increasing the solid content of the bonding layer coating solution will increase T. In some embodiments, the mass ratio of inorganic particles and binder in the bonding layer M1:M2 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 a range consisting of any two of these values.

[0047] In some embodiments, the second coating layer includes a nitrogen-containing material and a binder. In some embodiments, the second coating layer also includes inorganic particles. The present application does not particularly limit the content of nitrogen-containing materials, binders and inorganic particles, as long as the purpose of the present application can be achieved. For example, based on the total mass of nitrogen-containing materials, binders and inorganic particles, the mass percentage of nitrogen-containing materials is 60% to 95%, the mass percentage of binders is 0.5% to 10%, and the mass percentage of inorganic particles is 0% to 30%. The present application does not particularly limit the type of nitrogen-containing materials, as long as the purpose 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, symmetrical triaminotriazine or 2,3-dicyanopyrazine. The present application does not particularly limit the type of binder and inorganic particles, as long as the purpose of the present application can be achieved, for example, it can be at least one of the above-mentioned binders and the above-mentioned inorganic particles.

[0048] In some embodiments, the isolation film may have a thickness of 3 μm to 480 μm.

[0049] In some embodiments, the secondary battery further comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode 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 material layer comprises 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 consisting of any two values ​​therein. In the present application, the above-mentioned "positive electrode material layer located on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be arranged on one surface of the positive electrode current collector along its own thickness direction, or 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 it can be a partial area of ​​the surface of the positive electrode current collector. There is no special limitation in the present application, as long as the purpose of the present application can be achieved. The present application regulates 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 interaction force between the two is appropriate, which can make the positive electrode plate have higher strength. When the electrolyte of the present application is used, it can maintain better structural stability, and can make the secondary battery have a higher pass rate in the safety test. At the same time, it can reduce the gas production of the secondary battery during the cycle process and reduce the voltage drop, so that the secondary battery has better low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, while also having better low-temperature discharge performance and safety performance.

[0050] In some embodiments, 1≤E / F≤12.5. When the ratio E / F of the positive electrode current collector dyne value and the average particle size of the positive electrode active material is within the above range, the positive electrode sheet can have a higher strength, and can maintain better structural stability when the electrolyte of the present application is used, so that the secondary battery has better low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, and also has better low-temperature discharge performance and safety performance.

[0051] In some embodiments, 25≤E≤30. For example, E can be 25, 26, 27, 28, 29, 30, or a range consisting 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 suitable for the positive electrode active material, further improving the structural stability of the positive electrode sheet, so that the secondary battery has better low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, and also has better low-temperature discharge performance and safety performance.

[0052] In some embodiments, the specific surface area (BET) of the positive electrode active material is Sm 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 consisting of any two of these values. In the present application, the above-mentioned positive electrode active materials with different specific surface areas can be purchased, and then tested in combination with the test methods of the above-mentioned parameters provided below in this application to select the required positive electrode active materials. The positive electrode active material with a specific surface area within the above-mentioned range has an active specific surface area and structural strength adapted to the above-mentioned electrolyte, which is beneficial to improving the structural stability of the positive electrode sheet, and can make the secondary battery have a higher pass rate in the safety test, while being able to 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 anti-overcharge performance under high temperature and high pressure, while also having good low-temperature discharge performance, low-temperature rate performance and safety performance.

[0053] In some embodiments, the positive electrode active material contains aluminum. The present application does not particularly limit the preparation method containing aluminum in the positive electrode active material, as long as the purpose of the present application can be achieved, for example, it can be obtained by coating aluminum oxide 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 increased gas production at the interface, intense reactions between the positive and negative electrodes and the electrolyte, and the generation of more interfacial byproducts, resulting in poor low-temperature rate performance of the secondary battery and severe self-discharge, causing an increase in voltage drop. The positive electrode active material contains aluminum, and the aluminum element participates in the formation of the interfacial CEI film, which can increase 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, and make the secondary battery have good low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, while also having good low-temperature discharge performance, low-temperature rate performance and safety performance.

[0054] 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 consisting of any two of these values. In the present application, the positive electrode active materials of the above-mentioned different average particle sizes can be purchased, and then tested in combination with the test methods of the above-mentioned parameters provided below in the present application to select the desired positive electrode active materials. The positive electrode active material with an average particle size within the above-mentioned range has better adaptability to the positive electrode current collector, and can have better fit under a certain modulus of the positive electrode current collector, further improve the stability of the positive electrode sheet, and make the secondary battery have a higher pass rate in the safety test. At the same time, it can further reduce the voltage drop of the secondary battery, and further improve the low-temperature rate performance of the secondary battery, so that the secondary battery has better low-temperature floating charge performance and anti-overcharge performance under high temperature and high pressure, while also having better low-temperature discharge performance, low-temperature rate performance and safety performance.

[0055] The present application has no special restrictions on the positive electrode current collector, as long as the purpose 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). The present application has no special restrictions on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose 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, 10μm, 20μm, 40μm, 90μm, 400μm, 490μm, 500μm or a range consisting of any two of the values.

[0056] The present application has no particular restrictions on the positive electrode active material, as long as the purpose of the present application can be achieved. In some embodiments, the positive electrode active material may include but is not limited to lithium cobalt oxide (LiCoO 2 ), lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, nickel cobalt manganese oxide (for example, NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide or lithium nickel manganese oxide. In some embodiments, the positive electrode active material is lithium cobalt oxide or lithium iron phosphate. In some embodiments, the positive electrode active material may be doped and / or coated. In some embodiments, the positive electrode active material is doped with aluminum and / or coated with aluminum.

[0057] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductor. The present application does not particularly limit the types of the positive electrode binder and the positive electrode conductor, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene. At least one. For example, the positive electrode conductor may include but is not limited to conductive carbon black (Super P), graphene, carbon nanotubes or carbon fibers. Conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. Carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. Carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nanocarbon fibers. The present application has no particular restriction 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. Those skilled in the art can select the ratio according to actual needs as long as the purpose of the present application can be achieved.

[0058] In some embodiments, the surface of the positive electrode active material includes an aluminum oxide covering layer, and the thickness of the aluminum oxide covering layer is 1 μm to 1.5 μm.

[0059] In some embodiments, the surface of the positive active material includes at least one of lithium phosphate, lithium niobate or melamine, with a mass of 5% to 10% of the mass of the positive material layer. In some embodiments, the surface of the positive active material has α-crystalline polyvinylidene fluoride. In some embodiments, the surface of the positive active material includes at least one of lithium dihydrogen phosphate or aluminum dihydrogen phosphate, with a mass of 5% to 20% of the mass of the positive material layer.

[0060] In some embodiments, the secondary battery further includes a negative electrode sheet, and the separator is located between the positive electrode sheet and the negative electrode sheet. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or on two surfaces of the negative 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 negative electrode current collector, or it can be a partial area of ​​the surface of the negative electrode current collector. This application is not particularly limited, as long as the purpose of this application can be achieved. This application has no special restrictions on the negative electrode current collector, as long as the purpose of this application can be achieved, for example, it can include at least one of copper foil, nickel foil or carbon-based current collector. This application has no special restrictions on the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved, for example, the thickness of the negative electrode current collector can be 1μm to 200μm. The present application has no particular limitation on the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode 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 used.

[0061] In some embodiments, the negative electrode material layer includes a negative electrode active material. The present application has no particular restrictions on the negative electrode active material, 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-oxygen compounds, silicon-carbon compounds or silicon alloys.

[0062] In some embodiments, the negative electrode material layer may also 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. Conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. Carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. Carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. For example, the negative electrode binder may include but is not limited to at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylic acid salt, polyacrylic acid ester, polyvinyl pyrrolidone, polyimide, polysiloxane or styrene-butadiene rubber. It should be understood that the above materials are only exemplary, and the negative electrode material layer may use 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 may 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 conductor and the negative electrode binder in the negative electrode material layer can be (80~99):(0.5~10):(0.5~10). It should be understood that this is only exemplary and is not intended to limit the present application.

[0063] In some embodiments, the negative electrode material layer may further include a thickener. The present application does not particularly limit the type of the thickener, as long as the purpose of the present application can be achieved. For example, the thickener 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 thickener in the negative electrode material layer. Those skilled in the art may select according to actual needs, as long as the purpose of the present application can be achieved.

[0064] The secondary battery also includes a shell for accommodating a positive electrode plate, a separator, a negative electrode plate and an electrolyte, as well as other components known in the field of secondary batteries, and this application does not limit the above-mentioned other components. This application does not particularly limit the shell, and it can be a shell known in the art, as long as the purpose of this application can be achieved. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal, and this application does not limit the type of metal. A metal hard shell known in the art can be used, as long as the purpose of this application can be achieved. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0065] In some embodiments, the secondary battery is a lithium ion battery, but the application is not limited thereto.

[0066] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and there is no particular 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 order, and winding, folding and other operations as needed to obtain an electrode assembly of a winding structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly of a laminated structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the shell as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0067] In some embodiments, taking lithium-ion batteries 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, which is then placed in a shell such as an aluminum-plastic film, injected with electrolyte, formed, and packaged to make a lithium-ion battery.

[0068] 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 performance. The present application does not particularly limit the type of electronic device, and it can be used for 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 head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium ion capacitor, etc.

[0069] Example

[0070] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by mass.

[0071] Test methods and equipment:

[0072] Electrolyte component test:

[0073] The lithium-ion battery was disassembled to obtain the electrolyte, and the electrolyte components were tested using a gas chromatography-mass spectrometer (GC-MS, model: AgilentGC7890A). The mass percentages of the electrolyte components lithium salt additive, ethylene glycol bis(propionitrile) ether, 4,4'-diphenyl ether dicarboxylic acid, and methylene disulfonate were calculated using the external standard method.

[0074] Porosity test of the isolation film substrate layer:

[0075] Disassemble the lithium-ion battery to obtain the isolation membrane, scrape off the coating on the surface of the isolation membrane, and obtain the substrate layer of the isolation membrane. At a test temperature of 30°C, wrap the substrate layer flat with A4 paper, lay it flat on the die, and punch it with a punch. First, use a micrometer to measure the thickness of the substrate layer, calculate the apparent volume V1 of the substrate layer based on the surface area and thickness of the substrate layer, and then use a true density meter (model AccuPycⅡ) to test the true volume V2 of the substrate layer, and obtain the porosity P% of the substrate layer = (V1-V2) / V1×100%.

[0076] Average wall thickness test between adjacent holes in the isolation film bonding layer:

[0077] The separator was obtained by disassembling the lithium-ion battery. A scanning electron microscope (SEM) was used to test a 1μm×1μm area of ​​the separator bonding layer. The wall thickness between every two adjacent holes in 25 evenly distributed adjacent holes was measured, and the average value was calculated to obtain the average wall thickness T nm between adjacent holes in the bonding layer.

[0078] Apparent concentration ratio test of nitrogen and carbon:

[0079] The lithium-ion battery was disassembled to obtain the isolation membrane, and the surface of the second coating of the isolation membrane was measured by an energy dispersive spectrometer (EDS, model: EDAX Octane SDD). The apparent concentration of nitrogen and the apparent concentration of carbon in a 2μm×2μm area were tested at 30°C. The ratio of the apparent concentration of nitrogen to the apparent concentration of carbon, Y=apparent concentration of nitrogen / apparent concentration of carbon.

[0080] Dyne value test of positive electrode current collector:

[0081] Use a dyne pen (manufacturer: ACCU) with different dyne values ​​to draw lines on the surface of the positive electrode current collector along the belt and in the vertical direction. If the straight line does not shrink within 3 seconds, the dyne value is reached. Use a dyne pen with the same dyne value to test three times. If the straight line does not shrink within 3 seconds each time, the dyne value is the surface tension of the positive electrode current collector. For the positive electrode current collector in the lithium-ion battery, since the positive electrode current collector at the tab position is relatively flat, disassemble the lithium-ion battery, tear off the welded tab, and take the positive electrode current collector at the tab position for testing.

[0082] Average particle size test of positive electrode active material:

[0083] Disassemble the lithium-ion battery to obtain the positive electrode. Use a scanning electron microscope to take a SEM photo of the positive electrode to observe the positive electrode active material particles. Use image analysis software to randomly select 30 positive electrode active material particles from the SEM photo and calculate the area of ​​each particle. Assuming that the particles are spherical, calculate the particle size D (diameter) of each particle using the following formula: 2×(S1 / π) 1 / 2 , where S1 is the area of ​​the particle; the particle sizes of the 30 particles obtained are arithmetic averaged to obtain the average particle size of the positive electrode active material.

[0084] Specific surface area test of positive electrode active material:

[0085] In accordance with the national standard "Determination of the specific surface area of ​​solid substances by gas adsorption BET method" (GB / T 19587-2017), the specific surface area analyzer (model TristarⅡ3020M) was used to test the specific surface area of ​​the positive electrode active material by nitrogen adsorption method.

[0086] Detection of aluminum in positive electrode active materials:

[0087] Disassemble the lithium-ion battery to obtain the positive electrode. Use EDS to test the internal area of ​​the positive active material of the positive electrode to detect whether it contains aluminum.

[0088] Low temperature floating charge performance test:

[0089] Place the lithium-ion battery in a 0℃ constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge with a constant current of 1C to a voltage of 4.2V, charge with a constant voltage to a current of 0.05C, and then discharge with a constant current of 1C to a voltage of 2.8V, record the discharge capacity, and record it as the initial discharge capacity of the lithium-ion battery. Then charge with a constant current of 0.5C to a voltage of 4.2V, and charge with a constant voltage to a current of 0.05C. Transfer the lithium-ion battery to a 25℃ constant temperature box, and then charge with a constant voltage of 4.2V for 10 days. After 10 days, transfer the lithium-ion battery to a 0℃ constant temperature box, let it stand for 60 minutes, and discharge with a constant current of 1C to a voltage of 2.8V. Then charge with a constant current of 1C to a voltage of 4.2V, charge with a constant voltage to a current of 0.05C, and then discharge with a constant current of 1C to 2.8V, record the discharge capacity, and record it as the recoverable capacity of the lithium-ion battery. Low temperature floating charge capacity retention rate % = (initial discharge capacity - recoverable capacity) / initial discharge capacity × 100%.

[0090] Hot box test:

[0091] Charge the lithium-ion battery at a constant current of 0.5C to a cut-off voltage of 4.2V, then charge it at a constant voltage to a cut-off current of 200mA, and then let it stand for 5 minutes; attach a temperature-sensing wire to the fully charged lithium-ion battery, attach it between the two poles, connect the two poles to monitor the voltage, and hang the lithium-ion battery vertically in the hot box; heat the hot box to 145°C at a heating rate of 5°C and maintain it for 60 minutes, and observe the state of the lithium-ion battery during the process. 20 lithium-ion batteries of each embodiment or comparative example are tested as parallel samples. Judgment standard: The lithium-ion battery passes if it does not catch fire or explode. Hot box test pass rate (%) = number of hot box test passes / total number × 100%.

[0092] Overcharge test:

[0093] Under the condition of ambient temperature (60±5)℃, the lithium-ion battery is charged with 1C constant current to a voltage of 4.2V, constant voltage charged to a current of 0.05C, and then discharged with 1C constant current to a voltage of 2.8V. The discharged lithium-ion battery is charged with 0.25C constant current to 10V and then changed to constant voltage charging. Charging is stopped after charging for 5h. The passing standard is that the lithium-ion battery does not catch fire or explode. 20 lithium-ion batteries of each embodiment or comparative example are tested, and the number of batteries that pass the test is recorded. The overcharge test pass rate (%) = overcharge test pass number / total number × 100%.

[0094] Lithium deposition performance test:

[0095] Place the lithium-ion battery in a constant temperature box at 10°C. After 60 minutes, charge it to 4.2V at 2C constant current, charge it to 0.05C at 4.2V constant voltage, and let it stand for 5 minutes. Then discharge it to 2.5V at 0.5C constant current. This is one cycle. After 10 cycles of the above charge and discharge process, charge it to 4.2V at 2C constant current, charge it to 0.05C at 4.2V constant voltage, and let it stand for 5 minutes. Then disassemble the lithium-ion battery and observe the lithium deposition state on the surface of the negative electrode. The surface area without lithium deposition is golden yellow, and the lithium deposition area is grayish white.

[0096] The criteria for judging the degree of lithium deposition in lithium-ion batteries are as follows: a lithium deposition area of ​​0% means no lithium deposition, i.e., the degree of lithium deposition is zero; a lithium deposition area greater than 0 and less than or equal to 2% means mild lithium deposition, i.e., the degree of lithium deposition is mild; a lithium deposition area greater than 2% and less than or equal to 20% means moderate lithium deposition, i.e., the degree of lithium deposition is moderate; a lithium deposition area greater than 20% and less than or equal to 100% means severe lithium deposition, i.e., the degree of lithium deposition is severe, wherein the percentage of the lithium deposition area is calculated based on the total area of ​​the negative electrode material layer of the negative electrode plate.

[0097] Low temperature rate performance test:

[0098] At 25℃, 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℃, 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℃, 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℃ 1C low temperature retention rate (%) = D2 / D02×100%.

[0099] Gas production test:

[0100] 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.

[0101] Low temperature voltage drop test:

[0102] 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.

[0103] Drop performance test:

[0104] 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°).

[0105] 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.

[0106] 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.

[0107] Example 1-1

[0108] <Preparation of positive electrode sheet>

[0109] Take 1.2 g of aluminum nitrate nonahydrate (Al(NO 3 ) 3 9H 2 O) was added to the ethanol solution, stirred, 1 g of citric acid was added, stirred and dispersed for 2 h to form a dispersed system; 50 g of the positive electrode active material lithium cobalt oxide (LiCoO 2 , specific surface area Sm 2 / g is 0.20m 2 / g, average particle size F μm is 20.00 μm) was added to the above dispersion system, heated to 80°C and stirred for 48 hours to obtain a gel; the gel was placed in a vacuum drying oven at 115°C and dried for 50 hours, and then the dried gel was ground, sieved, and placed in a 200 mL crucible and heated in a tubular furnace N 2 The furnace was heated to 440°C at a rate of 5°C / min in an atmosphere for sintering, and kept at this temperature for 4 hours to prepare alumina-coated positive electrode material lithium cobalt oxide; the temperature of the tube furnace was lowered to 400°C, and N 2 Atmosphere switched to O 2 atmosphere, and heat-treat the carbon matrix for 4 hours to obtain a lithium cobalt oxide positive electrode material Al containing a nano-alumina coating layer. 2 O 3 Coated lithium cobalt oxide LiCoO 2 .

[0110] Al 2 O 3 Coated lithium cobalt oxide LiCoO 2, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97:1:2, and N-methylpyrrolidone (NMP) was added. 2800ppm of methyl acrylate, an acrylate-containing auxiliary agent, was added, and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 65wt%. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12μm and a dyne value E dyn / cm of 26dyn / cm. The aluminum foil was dried at 120°C for 1h to obtain a positive electrode sheet coated with a positive electrode active material layer with a thickness of 90μm on one side, and the surface density was 30mg / cm 2 Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. Then, after cold pressing, cutting, and slitting, it is dried under vacuum conditions at 120°C for 1 hour to obtain a positive electrode sheet with a size of 74mm (width) × 867mm (length), with an empty foil area for the positive electrode collector left at one end of the length direction.

[0111] Alumina (Dv50 is 2 μm) and binder PVDF are mixed at a mass ratio of 80:20, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a positive inorganic coating slurry with a solid content of 30 wt%. The positive inorganic coating slurry is evenly coated on one of the surfaces of the positive current collector empty foil area at the tail of the above-mentioned positive electrode sheet (this surface is defined as the a surface, and the other surface of the positive current collector is defined as the b surface), and dried at 120°C for 1 hour to obtain a positive electrode sheet with a positive inorganic coating on the a surface of the positive current collector, and the length of the positive inorganic coating is 95 mm and the thickness is 2.5 μm.

[0112] <Preparation of negative electrode sheet>

[0113] The negative electrode active material artificial graphite, conductive agent conductive carbon black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were mixed at a weight ratio of 96.5:1.5:1:1, deionized water was added, and the mixture was stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry was 75wt%. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12μm, and dried at 120°C to obtain a negative electrode sheet coated with a negative electrode material layer with a thickness of 90μm on one side, and the above steps were repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides, and then after cold pressing, cutting, and slitting, a negative electrode sheet with a specification of 76mm (width)×874mm (length) was obtained.

[0114] <Preparation of Electrolyte>

[0115] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC) is first heated at a high temperature of 60°C to convert it into a liquid state, and then ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) are prepared into a non-aqueous solvent in a mass ratio of 1:1:1, and then propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate, lithium salt additive lithium tetrafluoroborate, ethylene glycol bis(propionitrile) ether and 1,2,6-hexanetrinitrile are added and mixed evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage of propyl propionate is 31.000%, the mass percentage of fluoroethylene carbonate is 8.000%, the mass percentage of lithium hexafluorophosphate is 12.500%, the mass percentage A% of the lithium salt additive lithium tetrafluoroborate is 0.100%, the mass percentage B% of ethylene glycol bis(propionitrile) ether is 0.500%, the mass percentage of 1,2,6-hexanetrinitrile is 0.500%, and the balance is non-aqueous solvent.

[0116] <Preparation of Separator Film>

[0117] A polyethylene (PE) microporous membrane with a thickness of 8 μm and a porosity P% of 15% (provided by Shanghai Enjie Company) was used as the substrate layer of the separator. One surface of the substrate layer was defined as the c-surface, and the other surface was defined as the d-surface.

[0118] Preparation of isolation film c surface coating:

[0119] Inorganic boehmite particles with a Dv50 of 1.3µm and polyacrylate (weight-average molecular weight of 1.2 million to 2 million) were mixed in a mass ratio of 91:9 and dissolved in deionized water to form an inorganic coating slurry with a solid content of 43wt%. The inorganic coating slurry was then evenly coated on the c-side of the PE substrate layer using a micro-concave coating method and dried in an oven to obtain an isolation film with an inorganic coating with a thickness of 1.8μm coated on the c-side.

[0120] Add the first polymer polypropylene (PP) particles into the stirrer and stir evenly; add sodium carboxymethyl cellulose into the stirrer and stir evenly; add dimethylsiloxane, a wetting agent, into the stirrer, then add deionized water and stir, add nitrogen-containing material 2,3-dicyanopyrazine, binder polyvinylidene fluoride and inorganic particle boehmite, adjust the viscosity of the slurry to 45mPa•s and the solid content to 6wt%, and obtain the second coating slurry. The second coating slurry is coated on the surface of the inorganic coating on the c side of the isolation membrane in a stripe distribution manner, the stripe distribution is arranged parallel to the width of the isolation membrane, and the spacing between adjacent second coating stripes is 120μm. After drying in an oven, a second coating with a thickness of 3μm is obtained. Among them, the mass ratio of the first polymer, sodium carboxymethyl cellulose, dimethylsiloxane, 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 M3% of the nitrogen-containing material 2,3-dicyanopyrazine is 92%, the mass percentage M4% of the binder polyvinylidene fluoride is 7.8%, and the mass percentage M5% of the inorganic particle boehmite is 0.2%.

[0121] Preparation of isolation film d surface coating:

[0122] Inorganic boehmite particles with a Dv50 of 1.3µm and polyacrylate (weight-average molecular weight of 1.2 million to 2 million) were mixed in a mass ratio of 91:9 and dissolved in deionized water to form an inorganic coating slurry with a solid content of 47wt%. The inorganic coating slurry was then evenly coated on the d-side of the PE substrate layer using a micro-concave coating method and dried in an oven to obtain an isolation film with an inorganic coating with a thickness of 2.2μm coated on the d-side.

[0123] The inorganic particle boehmite and the binder polyvinylidene fluoride are mixed in a mass ratio of M1:M2=91:9, and then N-methylpyrrolidone is added and stirred evenly to obtain a bonding layer coating liquid with a solid content of 7wt%; the bonding layer coating liquid is coated on the surface of the inorganic coating on the d side of the isolation membrane by a dip coating method to form a wet film; the isolation membrane with the wet film is immersed in a coagulation liquid containing deionized water and N-methylpyrrolidone for phase inversion, and after immersion for 30s, it is placed in an oven and dried at 60°C for 2h to obtain an isolation membrane with a bonding layer (first coating) with a thickness of 3μm and an inorganic coating of 2.2μm on the d side, and a second coating with a thickness of 3μm and an inorganic coating of 1.8μm on the c side, wherein the mass percentage of N-methylpyrrolidone in the coagulation liquid is 38%, and the balance is deionized water, and the temperatures of the bonding layer coating liquid and the coagulation liquid are both 25°C.

[0124] <Preparation of lithium-ion batteries>

[0125] The positive electrode sheet, separator and negative electrode sheet prepared as above are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, wherein the a surface of the positive electrode sheet faces the c surface of the separator, and the electrode assembly is wound to obtain the electrode assembly. After welding the pole ears, the electrode assembly is placed in an outer packaging aluminum-plastic film, and after dehydration at 80°C, the above-mentioned electrolyte is injected, and a lithium-ion battery is obtained through vacuum packaging, standing, formation (the upper limit voltage of formation is 4.5V, the formation temperature is 70°C, and the formation standing time is 2 hours), shaping, capacity testing and other processes.

[0126] Example 1-2 to Example 1-24

[0127] Except that the type of lithium salt additive and its mass percentage A%, mass percentage of ethylene glycol bis(propionitrile) ether B% are adjusted as shown in Table 1 in <Preparation of electrolyte>, the mass percentage of non-aqueous solvent is changed accordingly, the mass percentage of propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate and 1,2,6-hexanetricarbonitrile remain unchanged, and the porosity P% of the isolation membrane substrate layer is adjusted as shown in Table 1 in <Preparation of isolation membrane>, the rest is the same as Example 1-1.

[0128] Example 2-1 to Example 2-5

[0129] In addition to adding 4,4'-diphenyl ether dicarboxylic acid according to Table 2 in <Preparation of Electrolyte>, and adjusting the mass percentage C% of 4,4'-diphenyl ether dicarboxylic acid as shown in Table 2, the mass percentage of the non-aqueous solvent changes accordingly, and the mass percentage of the lithium salt additive, ethylene glycol bis(propionitrile) ether, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate and 1,2,6-hexanetrinitrile remains unchanged, the rest is the same as Example 1-1.

[0130] Embodiment 2-6

[0131] In addition to adding 4,4'-diphenyl ether dicarboxylic acid according to Table 2 in <Preparation of Electrolyte>, and adjusting the mass percentage C% of 4,4'-diphenyl ether dicarboxylic acid as shown in Table 2, the mass percentage of the non-aqueous solvent changes accordingly, and the mass percentage of the lithium salt additive, ethylene glycol bis(propionitrile) ether, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate and 1,2,6-hexanetrinitrile remains unchanged, the rest is the same as Example 1-21.

[0132] Example 3-1 to Example 3-6

[0133] Except that methylene disulfonate is added in accordance with Table 3 in <Preparation of Electrolyte>, and the mass percentage content D% of methylene disulfonate is adjusted as shown in Table 3, the mass percentage content of the non-aqueous solvent changes accordingly, and the mass percentage content of the lithium salt additive, ethylene glycol bis(propionitrile) ether, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate and 1,2,6-hexanetrinitrile remains unchanged, the rest is the same as Example 1-1.

[0134] Embodiment 3-7

[0135] Except that methylene disulfonate is added in accordance with Table 3 in <Preparation of Electrolyte>, and the mass percentage content D% of methylene disulfonate is adjusted as shown in Table 3, the mass percentage content of the non-aqueous solvent changes accordingly, and the mass percentage content of the lithium salt additive, ethylene glycol bis(propionitrile) ether, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate and 1,2,6-hexanetrinitrile remains unchanged, the rest is the same as Example 1-21.

[0136] Example 4-1 to Example 4-6

[0137] Except that the preparation parameters of the adhesive layer on the d side of the isolation membrane were adjusted according to Table 4 in <Preparation of isolation membrane> so that the average wall thickness T nm between adjacent holes in the adhesive layer was as shown in Table 4, the rest was the same as Example 1-1.

[0138] Example 5-1 to Example 5-6

[0139] Except for adjusting the preparation parameters of the second coating on the c side of the isolation membrane according to Table 5 in <Preparation of Isolation Membrane> so that the apparent concentration of nitrogen element and the apparent concentration ratio Y of carbon element in the 2μm×2μm area on the surface of the second coating are as shown in Table 5, the rest is the same as Example 1-1.

[0140] Example 6-1 to Example 6-10

[0141] In addition to adjusting the average particle size F μm and specific surface area S m of the positive electrode active material according to Table 6 in <Preparation of positive electrode sheet> 2 Except for the above, the rest is the same as that of Example 1-1.

[0142] Embodiment 6-11

[0143] In addition to the positive electrode active material not being subjected to Al 2 O 3 Except for the coating, the rest is the same as Example 1-1, <Preparation of positive electrode sheet> is as follows:

[0144] The positive electrode active material is lithium cobalt oxide LiCoO 2 (Specific surface area S m 2 / g is 0.2m2 / g, average particle size F μm is 20μm), conductive carbon black (Super P), binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1:2, N-methylpyrrolidone (NMP) is added, 2800ppm of methyl acrylate containing acrylate additive is added, and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 65wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12μm and a dyne value Edyn / cm of 26dyn / cm, and the aluminum foil is dried at 120℃ for 1h to obtain a positive electrode sheet coated with a positive electrode active material layer with a thickness of 90μm on one side, and the surface density is 30mg / cm 2 Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. Then, after cold pressing, cutting, and slitting, it is dried under vacuum conditions at 120°C for 1 hour to obtain a positive electrode sheet with a size of 74mm (width) × 867mm (length), with an empty foil area for the positive electrode collector left at one end of the length direction.

[0145] Alumina (Dv50 is 2 μm) and binder PVDF are mixed at a mass ratio of 80:20, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a positive inorganic coating slurry with a solid content of 30 wt%. The positive inorganic coating slurry is evenly coated on one of the surfaces of the positive current collector empty foil area at the tail of the above-mentioned positive electrode sheet (this surface is defined as the a surface, and the other surface of the positive current collector is defined as the b surface), and dried at 120°C for 1 hour to obtain a positive electrode sheet with a positive inorganic coating on the a surface of the positive current collector, and the length of the positive inorganic coating is 95 mm and the thickness is 2.5 μm.

[0146] Comparative Example 1-1 to Comparative Example 1-8

[0147] Except that the mass percentage B% of ethylene glycol bis(propionitrile) ether is adjusted as shown in Table 1 in <Preparation of electrolyte>, the mass percentage of non-aqueous solvent is changed accordingly, the mass percentage of lithium salt additive, propyl propionate, fluoroethylene carbonate, lithium hexafluorophosphate and 1,2,6-hexanetricarbonitrile remain unchanged, and the porosity P% of the isolation membrane substrate layer is adjusted as shown in Table 1 in <Preparation of isolation membrane>, the rest is the same as Example 1-1.

[0148] Table 1

[0149]

[0150] Table 2

[0151]

[0152] Note: “ / ” in Table 2 indicates no corresponding preparation parameters.

[0153] Table 3

[0154]

[0155] Note: “ / ” in Table 3 indicates no corresponding preparation parameters.

[0156] Table 4

[0157]

[0158] Table 5

[0159]

[0160] Table 6

[0161]

[0162] 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, the type of the lithium salt additive of the present application is used and the value of A is regulated within the scope of the present application, and the content ratio A / B of the lithium salt additive and ethylene glycol bis(propionitrile) ether is regulated within the scope of the present application, and the isolation membrane with a porosity P of the substrate layer within the scope of the present application is matched, the prepared lithium ion battery has a higher low-temperature floating charge capacity retention rate, a higher hot box test pass rate and a higher overcharge test pass rate, indicating that the lithium ion battery has good low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure.

[0163] The value of the content C of 4,4'-diphenylether dicarboxylic acid usually affects the low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure of the lithium-ion battery. It can be seen from Examples 1-1, 2-1 to 2-5 and 1-21 and 2-6 that when the value of C is adjusted within the scope of this application, the prepared lithium-ion battery has a higher low-temperature floating charge capacity retention rate, a higher hot box test pass rate and a higher overcharge test pass rate, indicating that the lithium-ion battery has good low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure.

[0164] The value of the content D of methylene disulfonate usually affects the low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure of the lithium-ion battery. It can be seen from Examples 1-1, 3-1 to 3-6 and 1-21 and 3-7 that when the value of D is regulated within the scope of the present application, the prepared lithium-ion battery has a higher low-temperature floating charge capacity retention rate, a higher hot box test pass rate and a higher overcharge test pass rate, indicating that the lithium-ion battery has better low-temperature floating charge performance, safety performance and anti-overcharge performance under high temperature and high pressure.

[0165] The value of the average wall thickness T between adjacent holes in the isolation film bonding layer usually affects the low-temperature floating performance, safety performance, anti-overcharge performance under high temperature and high pressure, and low-temperature rate performance of the lithium-ion battery. It can be seen from Examples 1-1, 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 higher low-temperature floating capacity retention rate, a higher hot box test pass rate, a higher overcharge test pass rate, a better lithium precipitation situation, and a higher -10℃ 1C low temperature retention rate, indicating that the lithium-ion battery has better low-temperature floating performance, safety performance, anti-overcharge performance under high temperature and high pressure, and low-temperature rate performance.

[0166] On the surface of the second coating layer of the isolation membrane, the value of the ratio Y of the apparent concentration of nitrogen element to the apparent concentration of carbon element usually affects the low-temperature floating performance, safety performance, anti-overcharge performance under high temperature and high pressure, and low-temperature discharge performance of the lithium-ion battery. From Example 1-1, Example 5-1 to Example 5-6, it can be seen that by adjusting the value of Y within the scope of this application, the prepared lithium-ion battery has a higher low-temperature floating capacity retention rate, a higher hot box test pass rate, a higher overcharge test pass rate, a lower gas production, a lower low-temperature voltage drop, and a higher drop test pass rate, indicating that the lithium-ion battery has better low-temperature floating performance, safety performance, anti-overcharge performance under high temperature and high pressure, and low-temperature discharge performance.

[0167] 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 usually affect the low-temperature floating performance, safety performance, anti-overcharge performance under high temperature and high pressure, low-temperature discharge performance and low-temperature rate performance of the lithium-ion battery. From Example 1-1, Example 6-1 to Example 6-10, it can be seen that by regulating the values ​​of E / F, S, and F within the scope of this application, the prepared lithium-ion battery has a higher low-temperature floating capacity retention rate, a higher hot box test pass rate, a higher overcharge test pass rate, a lower gas production, a lower low-temperature voltage drop, a higher drop test pass rate, and a higher -10℃ 1C low-temperature retention rate, indicating that the lithium-ion battery has good low-temperature floating performance, safety performance, anti-overcharge performance under high temperature and high pressure, low-temperature discharge performance, and low-temperature rate performance.

[0168] The presence of aluminum in the positive active material usually affects the low-temperature floating charge performance, safety performance, anti-overcharge performance under high temperature and high pressure, low-temperature discharge performance and low-temperature rate performance of the lithium-ion battery. It can be seen from Examples 1-1 and 6-11 that the lithium-ion battery containing aluminum in the positive active material has a higher low-temperature floating charge capacity retention rate, a higher hot box test pass rate, a higher overcharge test pass rate, a lower gas production, a lower low-temperature voltage drop, a higher drop test pass rate and a higher -10℃ 1C low-temperature retention rate, indicating that the lithium-ion battery has good low-temperature floating charge performance, safety performance, anti-overcharge performance under high temperature and high pressure, low-temperature discharge performance and low-temperature rate performance.

[0169] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method or article.

[0170] The terms "one of", "one of", "a kind of" or other similar terms connected to the elements refer to any one of the listed elements. For example, "one of A or B" means only A or only B; as another example, "one of A, B, and C" means only A, only B, or only C. The terms "at least one of", "at least one of", "at least one of" or other similar terms connected to the elements refer to any combination of the listed elements. For example, "at least one of A or B" means only A, only B, A and B. As 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, B, and C.

[0171] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0172] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, wherein: The secondary battery comprises an electrolyte and a separator, wherein the electrolyte comprises a lithium salt additive and ethylene glycol bis(propionitrile) ether, wherein the mass percentage of the lithium salt additive is A%, the mass percentage of the ethylene glycol bis(propionitrile) ether is B%, and 0.035≤A / B≤20 based on the total mass of the electrolyte; and 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 isolation film includes a substrate layer, and the porosity of the substrate layer is P%, and 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 comprises 4,4'-diphenyl ether dicarboxylic acid. Based on the total mass of the electrolyte, the mass percentage of the 4,4'-diphenyl ether dicarboxylic acid is C%, and 0.5≤C≤2.

5.

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

5.

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

8. The secondary battery according to any one of claims 1 to 6, wherein The isolation film also includes a second coating located on at least one surface of the substrate layer. On the surface of the second coating, within an area of ​​2μm×2μm, the ratio of the apparent concentration of nitrogen element to the apparent concentration of carbon element is Y, 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 also includes a positive electrode plate, which includes a positive electrode collector and a positive electrode material layer located on at least one surface of the positive electrode collector, the dyne value of the positive electrode collector is Edyn / cm, the positive electrode material layer includes a positive electrode active material, and the average particle size of the positive electrode active material is F μm, 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 S m 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