CN116666732A

CN116666732A - Secondary battery and electronic device

Info

Publication number: CN116666732A
Application number: CN202310806116.3A
Authority: CN
Inventors: 刘建; 蔡鑫; 郑湘岭; 唐超
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2023-07-03
Filing date: 2023-07-03
Publication date: 2023-08-29

Abstract

The application provides a secondary battery and an electronic device. The secondary battery comprises a positive electrode plate, a negative electrode plate, a diaphragm and electrolyte, wherein the electrolyte comprises a compound shown in a formula (I), the mass percentage of the compound shown in the formula (I) is x% which is more than or equal to 0.01 and less than or equal to 3, the diaphragm comprises a substrate layer and a bonding layer, the thickness of the bonding layer is h mu m, and x/h is more than or equal to 0.0004 and less than or equal to 0.6. The electrolyte and the diaphragm which are prepared from the compound shown in the formula (I) are applied to the secondary battery, and the values of x and x/h are regulated and controlled within the range of the application, so that a solid electrolyte interface film with good thermal stability can be formed on the surface of the negative electrode plate, the thermal stability of the negative electrode plate is improved, and the cycle performance of the secondary battery is improved, and the high-temperature safety performance of the secondary battery is improved.

Description

Secondary battery and electronic device

Technical Field

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

Background

The secondary battery, such as a lithium ion battery, has the advantages of high energy storage density, high open circuit voltage, low self-discharge rate, long cycle life, good safety and the like, and is widely used as a power supply for electronic products such as cameras, mobile phones, unmanned aerial vehicles, notebook computers, intelligent watches and the like. With the continuous expansion of the application range of lithium ion batteries, the market has set higher requirements for lithium ion batteries.

Through setting up the tie coat and bonding diaphragm and negative pole piece together on the diaphragm surface, can shorten the transmission path of lithium ion, improve the transmission capacity of lithium ion and improve the cycle performance of secondary battery, but can influence the heat dissipation of the interface between diaphragm and the negative pole piece, and then influence the thermal stability of negative pole piece, lead to lithium ion battery's high temperature security performance poor.

Disclosure of Invention

The application aims to provide a secondary battery and an electronic device, which are used for combining the cycle performance and the high-temperature safety performance of the secondary battery. The specific technical scheme is as follows:

a first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte comprising a compound represented by formula (I):

wherein R is ₁ Selected from O or-CH (Ra) -, ra is selected from H, F, C ₁ To C ₅ Alkyl or C of (2) ₁ To C ₅ Alkoxy groups of (a); r is R ₂ And R is ₃ Each independently selected from H, F, C ₁ To C ₅ Alkyl, C of (2) ₁ To C ₅ Alkoxy or C of (2) ₂ To C ₅ Alkenyl, C ₂ To C ₅ Alkynyl of (a); r is R ₄ Independently selected from H, F, C unsubstituted or substituted with F ₁ To C ₅ Alkyl, C of (2) ₁ To C ₅ Alkoxy, C ₂ To C ₅ Alkenyl or C of (2) ₂ To C ₅ Alkynyl of (a); based on the mass of the electrolyte The mass percentage of the compound shown in the formula (I) is x.0.01-3, preferably 0.1-2.5; the separator comprises a substrate layer and a bonding layer, wherein the thickness of the bonding layer is h mu m, x/h is more than or equal to 0.0004 and less than or equal to 0.6, and preferably, x/h is more than or equal to 0.005 and less than or equal to 0.4. For example, the value of x may be 0.01, 0.05, 0.1, 0.3, 0.5, 0.8, 1, 1.5, 2, 2.5, 3 or a range of any two of the values, and the value of x/h may be 0.0004, 0.0008, 0.001, 0.002, 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or a range of any two of the values.

The diaphragm in the secondary battery provided by the application comprises the substrate layer and the bonding layer, has better bonding property with the negative electrode, can effectively shorten the transmission path of lithium ions, improve the transmission capacity of the lithium ions and improve the cycle performance of the secondary battery, but can influence the dissipation of interfacial heat between the diaphragm and the negative electrode plate, further influence the thermal stability of the negative electrode plate, and reduce the high-temperature safety performance of the secondary battery. The compound shown in the formula (I) in the electrolyte can form a solid electrolyte interface film with high ion conductivity on the surface of the negative electrode plate, has a good lithium ion transmission effect, and the formed solid electrolyte interface film has good thermal stability and mechanical property, so that the cycle performance (such as high-temperature cycle performance) and high-temperature safety performance can be improved. Therefore, when the electrolyte comprising the compound shown in the formula (I) and the diaphragm are applied to the secondary battery, a solid electrolyte interface film with good thermal stability can be formed on the surface of the negative electrode plate, so that the thermal stability of the negative electrode plate is improved, and the cycle performance and the high-temperature safety performance of the secondary battery are both realized. In addition, the thermal stability and mechanical properties of the solid electrolyte interface film are improved, and the high-temperature storage performance of the secondary battery can be improved; the compound shown in the formula (I) in the diaphragm and the electrolyte can improve the transmission performance of lithium ions, so that the secondary battery provided by the application also has good low-temperature performance, such as low-temperature cycle performance, low-temperature discharge performance and the like. When x is too small, for example, less than 0.01, the content of the compound shown in the formula (I) is too small, so that the problem of heat dissipation of an interface between the diaphragm and the negative electrode plate cannot be solved, and the heat stability of the negative electrode plate is not improved, so that the high-temperature safety performance and the high-temperature storage performance of the secondary battery are not improved. When x is excessively large, for example, more than 3, the content of the compound represented by formula (I) is excessively large, which may cause an excessively thick solid electrolyte interface film formed on the surface of the negative electrode, increasing the transmission resistance of lithium ions, thereby being disadvantageous in improving the cycle performance and low temperature performance of the secondary battery. When x/h is too small (for example, less than 0.0004) or x/h is too large (for example, more than 0.6), the synergistic effect of the electrolyte and the diaphragm of the application is difficult to be exerted, so that the stability of the negative electrode plate is poor, the interface impedance of the negative electrode is too large, and the cycle performance, the high-temperature safety performance and the low-temperature performance of the secondary battery are affected. Therefore, the electrolyte comprising the compound shown in the formula (I) and the diaphragm are applied to the secondary battery, and the values of x and x/h are regulated and controlled within the range of the application, so that the cycle performance and the high-temperature safety performance of the secondary battery are both considered, and the secondary battery has good high-temperature storage performance and low-temperature performance. In the present application, the above-mentioned "high temperature" means a temperature of 40 ℃ or higher and the "low temperature" means a temperature of 0 ℃ or lower.

In some embodiments of the application, 5.ltoreq.h.ltoreq.25, preferably 6.ltoreq.h.ltoreq.20. The value of h may be 5, 5.2, 6, 7, 8, 10, 12, 15, 18, 20, 22, 23, 24, 25 or a range of any two values therein. By regulating the value of the bonding layer thickness h within the range of 5 to 25, the low-temperature cycle performance, the low-temperature discharge performance, the high-temperature cycle performance and the high-temperature safety performance of the secondary battery can be improved.

In the present application, the above features 0.1.ltoreq.x.ltoreq.2.5, 6.ltoreq.h.ltoreq.20, 0.005.ltoreq.x/h.ltoreq.0.4 may be arbitrarily combined as long as the object of the present application can be achieved. By regulating at least one of x, h and x/h to satisfy 0.1-2.5, 6-20 and 0.005-0.4, the low temperature cycle performance, low temperature discharge performance, high temperature cycle performance and high temperature safety performance of the secondary battery can be further improved. In some embodiments, 0.1.ltoreq.x.ltoreq.2.5, 6.ltoreq.h.ltoreq. 20,0.005.ltoreq.x/h.ltoreq.0.4. By regulating and controlling the values of x, h and x/h to meet the requirements of x being more than or equal to 0.1 and less than or equal to 2.5, h being more than or equal to 6 and less than or equal to 20, and x/h being more than or equal to 0.005 and less than or equal to 0.4, the low-temperature cycle performance, low-temperature discharge performance, high-temperature cycle performance and high-temperature safety performance of the secondary battery can be further improved.

In some embodiments of the present application, the compound of formula (I) comprises at least one of the following compounds:

In the secondary battery, the electrolyte comprises the compound shown in the formula (I) in the range, so that the heat stability of the negative electrode plate can be better improved, a solid electrolyte interface film with good lithium ion transmission characteristic is formed on the surface of the negative electrode, and the transmission resistance of lithium ions is reduced, thereby further improving the cycle performance, the high-temperature safety performance, the low-temperature performance and the high-temperature storage performance of the secondary battery.

In some embodiments of the application, the adhesion between the separator and the negative electrode tab is 3N/m to 29N/m, preferably 5N/m to 28N/m. For example, the adhesion between the separator and the negative electrode sheet may have a value of 3, 4, 5, 8, 10, 12, 15, 18, 20, 23, 25, 26, 28, 29 or a range of any two values therein. The secondary battery provided by the application regulates and controls the adhesion between the diaphragm and the negative electrode plate to be in the range of 3N/m to 29N/m, which shows that the diaphragm and the negative electrode have good adhesion, and the transmission performance of lithium ions can be improved, so that the low-temperature performance and the cycle performance of the secondary battery are improved. Meanwhile, by combining the electrolyte containing the compound shown in the formula (I), the obtained secondary battery can better give consideration to the cycle performance and the high-temperature safety performance, and has good low-temperature performance and high-temperature storage performance. In other embodiments of the present application, the adhesion between the separator and the negative electrode tab is in the range of 5N/m to 28N/m, enabling further improvement in low temperature performance of the secondary battery. And simultaneously, the electrolyte containing the compound shown in the formula (I) can further improve the cycle performance, the high-temperature safety performance, the low-temperature performance and the high-temperature storage performance of the secondary battery.

In some embodiments of the application, the tie layer comprises a first tie layer comprising a first binder comprising at least one of vinylidene fluoride, hexafluoropropylene, or an ethylene-propylene-maleic anhydride copolymer; wherein the mass ratio of ethylene, propylene and maleic anhydride in the ethylene-propylene-maleic anhydride copolymer is (5 to 15): 70 to 95): 3 to 8. The mass ratio of ethylene, propylene and maleic anhydride in the ethylene-propylene-maleic anhydride copolymer may be, for example, 5:90:5, 7:88:5, 10:85:5, 12:85:3, 15:77:8 or a range of any two values therein. When the separator adopting the first binder type in the range of the application is applied to the secondary battery, the secondary battery has better high-temperature safety performance, high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance, low-temperature cycle performance and the like. The weight average molecular weight of the ethylene-propylene-maleic anhydride copolymer is not particularly limited in the present application as long as the object of the present application can be achieved, for example, the weight average molecular weight of the maleic anhydride copolymer may be 300000 to 1000000.

In some embodiments of the application, the tie layer comprises a second tie layer comprising a second binder comprising at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, or styrene-butyl acrylate-methyl acrylate copolymer, wherein the mass ratio of styrene, butyl acrylate, and methyl acrylate in the styrene-butyl acrylate-methyl acrylate copolymer is (50 to 70): 10 to 30. The mass ratio of styrene, butyl acrylate to methyl acrylate in the styrene-butyl acrylate-methyl acrylate copolymer may be, for example, 50:20:30, 52:22:26, 55:30:15, 55:20:25, 60:10:30, 60:20:20, 60:30:10, 65:18:27, 70:20:10 or a range of any two values therein. When the separator adopting the second binder type in the range of the application is applied to the secondary battery, the secondary battery has better high-temperature safety performance, high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance and low-temperature cycle performance. The weight average molecular weight of the styrene-butyl acrylate-methyl acrylate copolymer is not particularly limited in the present application as long as the object of the present application can be achieved, for example, the weight average molecular weight of the styrene-butyl acrylate-methyl acrylate copolymer may be 300000 to 1000000.

In some embodiments of the application, the adhesive layer comprises a first adhesive layer having a thickness of 5 μm to 20 μm and a second adhesive layer having a thickness of 0.2 μm to 4 μm. For example, the first adhesive layer thickness may have a value of 5, 6, 8, 10, 12, 13, 15, 16, 18, 19, 20 or a range of any two of the values, and the second adhesive layer thickness may have a value of 0.2, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4 or a range of any two of the values. In some embodiments, the substrate layer is positioned between a first tie layer and a second tie layer, the first tie layer facing the positive electrode and the second tie layer facing the negative electrode. In other embodiments, the substrate layer is positioned between a first tie layer and a second tie layer, the first tie layer facing the negative electrode and the second tie layer facing the positive electrode. The secondary battery provided by the application has the advantages that the thickness of the first bonding layer and the thickness of the second bonding layer of the diaphragm are regulated and controlled within the range of the application, the bonding property of the diaphragm and the negative electrode is improved, and meanwhile, the transmission performance of lithium ions is considered, so that the low-temperature performance, the high-temperature cycle performance and the high-temperature safety performance of the secondary battery are improved.

In the present application, the adhesive force between the above-mentioned characteristic separator and the negative electrode sheet is 3N/m to 29N/m, the adhesive layer includes a first adhesive layer including a first adhesive agent, the first adhesive agent includes at least one of vinylidene fluoride, hexafluoropropylene or an ethylene-propylene-maleic anhydride copolymer, the adhesive layer includes a second adhesive agent, the second adhesive agent includes at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate or a styrene-butyl acrylate-methyl acrylate copolymer, the adhesive layer includes a first adhesive layer and a second adhesive layer, the base material layer is located between the first adhesive layer and the second adhesive layer, the thickness of the first adhesive layer is 5 μm to 20 μm, and the thickness of the second adhesive layer is 0.2 μm to 4 μm, which can be arbitrarily combined as long as the object of the present application can be achieved.

In some embodiments of the application, the electrolyte further comprises a carboxylate compound comprising at least one of propyl propionate, ethyl acetate, methyl pivalate, methyl valerate, 2-difluoroethyl propionate, or 2, 2-difluoroethyl acetate; based on the mass of the electrolyte, the mass percentage of the carboxylate compound is y.ltoreq.y.ltoreq.72. For example, y may have a value of 25, 28, 30, 33, 35, 40, 50, 60, 62, 65, 70, 72 or a range of any two values therein. The carboxylic ester compound has lower viscosity and lower melting point, and the carboxylic ester compound is further introduced into the original electrolyte, so that the viscosity of the electrolyte can be further reduced, and the low-temperature performance of the secondary battery is improved. In the secondary battery, the electrolyte comprises the carboxylic ester compound in the range, and the content of the carboxylic ester compound is regulated and controlled in the range, so that the secondary battery has better high-temperature safety performance and high-temperature cycle performance and better low-temperature performance.

In some embodiments of the application, the electrolyte further comprises a compound of formula (II) comprising at least one of a compound of formula (II-1) or a compound of formula (II-2),

wherein R is ₂₁ And R is ₂₂ Each independently selected from H, C ₁ To C ₄ N is 1 or 2; d and E are each independently selected from C ₁ To C ₈ An alkylene group of (a); based on the mass of the electrolyte, the mass percentage of the compound in the formula (II) is a percent, and a is more than or equal to 0.2 and less than or equal to 5. For example, the value of a may be 0.2, 0.3, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range of any two values therein. In the secondary battery, the electrolyte is further introduced into the compound of the formula (II) and the content of the compound of the formula (II) is regulated and controlled within the range, the compound of the formula (II) can form a stable interface protection layer at the interface of the negative electrode, so that the contact between the electrolyte and the interface of the negative electrode can be effectively reduced, the side reaction of the electrolyte at the interface of the negative electrode is reduced, and the interface impedance is reduced; when used in combination with a compound of formula (I), the composition is easy to form a polymer having better ionic conductivity and heat at the interface of the anodeAnd a stable solid electrolyte interface film, thereby further improving the low temperature cycle performance, low temperature discharge performance, high temperature cycle performance, and high temperature safety performance of the secondary battery.

In some embodiments of the present application, the compound of formula (II-1) comprises at least one of 1, 3-propane sultone, 1, 4-butane sultone, 5-methyl oxathiolane 2, 2-dioxide, 2, 4-butane sultone. In the secondary battery of the present application, when the electrolyte solution includes the compound represented by the formula (I) and the compound represented by the formula (II-1) within the above-mentioned range, a synergistic effect can be further exerted, and the low-temperature performance, the high-temperature cycle performance and the high-temperature safety performance of the secondary battery can be further improved.

In some embodiments of the present application, the compound of formula (II-2) comprises at least one of methylene methane disulfonate or ethylene methane disulfonate. In the secondary battery of the present application, when the electrolyte solution comprises the compound represented by the formula (I) and the compound represented by the formula (II-2) within the above-mentioned range, the synergistic effect can be further exerted, and the low-temperature performance, the high-temperature cycle performance and the high-temperature safety performance of the secondary battery can be better improved.

In some embodiments of the present application, when the electrolyte solution includes the compound of formula (I) and the compound of formula (II-1) and the compound of formula (II-2) within the above-described ranges, the synergistic effect can be better exerted, and the low temperature performance, the high temperature cycle performance and the high temperature safety performance of the secondary battery can be better improved.

In the present application, the electrolyte further includes a lithium salt, the present application is not particularly limited in kind, and a lithium salt known in the art may be used, and illustratively, the lithium salt may include at least one of lithium hexafluorophosphate, lithium bis (trifluoromethanesulfonyl) imide, lithium bis (fluorosulfonyl) imide, lithium difluorophosphate, lithium bis (oxalato) borate, or lithium difluorooxalato borate, but is not limited thereto. The content of the lithium salt in the electrolyte is not particularly limited as long as the object of the present application can be achieved, for example, the content of the lithium salt is 10 to 15% by mass based on the mass of the electrolyte.

In the application, the electrolyte further comprises a nonaqueous organic solvent, wherein the nonaqueous organic solvent comprises at least one of non-fluorinated cyclic carbonate or non-fluorinated chain carbonate; the non-fluorinated cyclic carbonate comprises at least one of ethylene carbonate, propylene carbonate, hexene carbonate, or octene carbonate; the non-fluorinated chain carbonate includes at least one of diethyl carbonate, dimethyl carbonate, methylethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, dioctyl carbonate, dipentyl carbonate, ethylisobutyl carbonate, isopropyl methyl carbonate, di-n-butyl carbonate, diisopropyl carbonate, or propyl carbonate.

In some embodiments, the electrolyte includes a compound of formula (I), a lithium salt, and a non-aqueous organic solvent as described above. Wherein the mass percentage of the compound represented by formula (I) and the lithium salt is as described above, and the mass percentage of the nonaqueous organic solvent is 82% to 89% based on the mass of the electrolyte. The secondary battery comprising the electrolyte has good low-temperature performance, high-temperature cycle performance and high-temperature safety performance.

In some embodiments, the electrolyte includes a compound of formula (I), a lithium salt, a compound of formula (II), and a non-aqueous organic solvent as described above. Wherein the mass percent of the compound shown in the formula (I), the lithium salt and the compound shown in the formula (II) is 77-89% of the mass percent of the nonaqueous organic solvent based on the mass of the electrolyte. The secondary battery comprising the electrolyte can further improve low-temperature performance, high-temperature cycle performance and high-temperature safety performance.

In some embodiments, the electrolyte includes a compound of formula (I), a lithium salt, a carboxylic acid ester compound, and the non-aqueous organic solvent described above. Wherein the mass percent of the compound shown in the formula (I), the lithium salt and the carboxylic ester compound is 10-64 percent based on the mass of the electrolyte. The secondary battery comprising the electrolyte can further improve low-temperature performance, high-temperature cycle performance and high-temperature safety performance.

In some embodiments, the electrolyte includes a compound of formula (I), a lithium salt, a compound of formula (II), a carboxylate compound, and the non-aqueous organic solvent described above. Wherein the mass percent of the compound shown in the formula (I), the lithium salt, the compound shown in the formula (II) and the carboxylic ester compound is 5-64% based on the mass of the electrolyte. The secondary battery comprising the electrolyte has better low-temperature performance, high-temperature cycle performance and high-temperature safety performance.

In some embodiments of the present application, the positive electrode sheet comprises a positive electrode material, the positive electrode material comprises an element M, the element M comprises at least one of Al, mg, zr, ti or La, and the mass percentage of the element M is b% or less, 0.01% or less, and b% or less, 3% or less, based on the mass of the positive electrode material. For example, the value of b may be 0.01, 0.05, 0.1, 0.3, 0.5, 0.8, 1, 1.5, 2, 2.5, 3 or a range of any two values therein. In the secondary battery, the positive electrode plate comprises the M element and the content of the M element is regulated and controlled within the range, so that the bulk structural stability of a positive electrode material and the diffusion dynamics of the surface of the positive electrode plate can be effectively ensured, the positive electrode plate has lower interface impedance, a compound shown in a formula (I) in electrolyte is combined to form a low-impedance solid electrolyte interface film, and the high-cohesiveness diaphragm is combined to effectively improve the ion transmission capacity of the positive electrode side, so that the low-temperature performance of the secondary battery is improved under the condition of further ensuring high-temperature stability, and the low-temperature discharge performance, the low-temperature cycle performance, the high-temperature cycle performance and the high-temperature storage performance of the secondary battery are further improved.

In the present application, the manner of doping the M element in the positive electrode material is not particularly limited as long as the object of the present application can be achieved; illustratively, sintering a mixture comprising a positive electrode active material precursor material at a temperature of 600 ℃ to 1500 ℃ to obtain a primary positive electrode active material; sintering a raw material containing a primary positive electrode active material and a compound containing an M element at a temperature of 600-1000 ℃ to obtain the positive electrode material; wherein the mixture of positive electrode active material precursor materials may include, but is not limited to, co ₃ O ₄ 、Li ₂ CO ₃ 、Ni _x Co _y Mn _(1-x-y) (OH) ₂ At least two of LiOH, and the primary positive electrode active material such as LiCoO ₂ Or LiNiCoMnO ₂ ComprisesStarting materials for compounds of element M, e.g. Al ₂ O ₃ 、MgO、ZrO ₂ 、TiO ₂ 、La ₂ O ₃ At least one of them.

In some embodiments of the application, the particle size Dv50 of the positive electrode material is 10 μm to 15 μm. For example, the Dv50 value may be 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15 or a range of any two values therein. In the secondary battery, the cathode material with the Dv50 in the range of 10-15 mu m is adopted, so that the low-temperature cycle performance and the high-temperature cycle performance of the secondary battery can be further improved on the basis of better high-temperature safety performance.

In some embodiments of the application, the particle size Dv99 of the positive electrode material is 20 μm to 45 μm. For example, dv99 may have a value of 20, 21, 22, 23, 25, 26, 27, 28, 29, 30, 32, 33, 35, 36, 38, 40, 42, 43, 44, 45 or a range of values consisting of any two of these values. In the secondary battery, the cathode material with the Dv99 in the range of 20-45 μm is adopted, so that the low-temperature cycle performance and the high-temperature cycle performance of the secondary battery can be further improved on the basis of better high-temperature safety performance.

In some embodiments of the application, the particle sizes Dv50 and Dv99 of the positive electrode material satisfy: dv99/Dv50 is less than or equal to 1.5 and less than or equal to 4.5. For example, the Dv99/Dv50 value may be 1.5, 1.6, 1.7, 1.8, 2, 2.2, 2.3, 2.5, 2.6, 2.8, 3, 3.2, 3.5, 3.6, 3.8, 4, 4.2, 4.3, 4.5 or a range of values consisting of any two of these values. The particle size Dv99/Dv50 of the positive electrode material is regulated within the range of 1.5 to 4.5, and the low-temperature cycle performance and the high-temperature cycle performance of the secondary battery can be further improved on the basis of better high-temperature safety performance.

In the present application, the features in the above embodiments are: the characteristics of Dv50 of 10 μm to 15 μm, dv99 of 20 μm to 45 μm, dv99/Dv50 of 1.5.ltoreq.Dv99.ltoreq.4.5 and the like may be arbitrarily combined as long as the object of the present application can be achieved. In the secondary battery, the positive electrode material in the particle range has good lithium removal kinetics and relatively low specific surface area, so that the reaction between electrolyte and the positive electrode plate interface can be reduced, the heat generation caused by side reaction is reduced, and meanwhile, the positive electrode material in the particle range also has good electrode plate processing type, and plays a key role in the stability and consistency of the battery performance; when the above positive electrode material satisfies at least two of Dv50 of 10 μm to 15 μm, dv99 of 20 μm to 45 μm, and 1.5.ltoreq.Dv99/Dv50.ltoreq.4.5, the low temperature cycle performance and the high temperature cycle performance of the secondary battery can be further improved. When the above positive electrode material satisfies both of 10 μm to 15 μm in Dv50, 20 μm to 45 μm in Dv99, 1.5.ltoreq.Dv99/Dv50.ltoreq.4.5, the low temperature cycle performance and the high temperature cycle performance of the secondary battery can be improved even further.

In the present application, the term "Dv50" means a particle diameter in which the cumulative distribution of the particle volume is 50%; i.e. the volume content of particles smaller than this particle size is 50% of the total particles. The term "Dv99" means a particle size with a cumulative distribution of particle volume of 99%; i.e. the volume content of particles smaller than this particle size is 99% of the total particles. The manner of obtaining the positive electrode material having the particle diameters Dv50, dv99 within the above-described range is not particularly limited in the present application, as long as the object of the present application can be achieved; illustratively, the means may be selected from mechanical comminution, ball milling or jet milling.

In some embodiments of the present application, a positive electrode tab includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer may be disposed on one surface of the positive electrode current collector in the thickness direction thereof, or may be disposed on both surfaces of the positive electrode current collector in the thickness direction thereof. The "surface" here may be the entire region of the positive electrode current collector or may be a partial region of the positive electrode current collector, and the present application is not particularly limited as long as the object of the present application can be achieved. The positive electrode current collector of the present application is not particularly limited as long as the object of the present application can be achieved, and may include, for example, aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector), or the like. The thicknesses of the positive electrode current collector and the positive electrode material layer are not particularly limited as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 6 μm to 12 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm. The thickness of the positive electrode sheet is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the positive electrode sheet is 50 μm to 250 μm.

The positive electrode material layer of the present application includes the above positive electrode material including a substance capable of reversibly intercalating and deintercalating active ions such as lithium ions. The positive electrode material layer may be one or more layers, and each of the multiple positive electrode material layers may contain the same or different positive electrode materials. The positive electrode material of the present application may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO) ₂ ) At least one of lithium manganate, lithium iron manganese phosphate or lithium titanate.

In the present application, the positive electrode material layer further includes a conductive agent and a binder, and the present application is not particularly limited in kind as long as the object of the present application can be achieved, and for example, the conductive agent may include, but is not limited to, at least one of acetylene black, conductive carbon black (Super P), carbon Nanotubes (CNTs), carbon fibers, crystalline graphite, ketjen black, graphene, a metal material, or a conductive polymer. The carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and/or multi-walled carbon nanotubes. The carbon fibers may include, but are not limited to, vapor Grown Carbon Fibers (VGCF) and/or nano carbon fibers. The above-mentioned metal material may include, but is not limited to, metal powder and/or metal fiber, and in particular, the metal may include, but is not limited to, at least one of copper, nickel, aluminum or silver. The conductive polymer may include, but is not limited to, at least one of a polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber, or polyvinylidene fluoride. The mass ratio of the positive electrode material, the conductive agent and the binder in the positive electrode material layer is not particularly limited, and can be selected by a person skilled in the art according to actual needs as long as the purpose of the application can be achieved.

Optionally, the positive electrode sheet may further comprise a conductive layer located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited, and may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application, and for example, at least one of the conductive agent and the binder may be used.

In some embodiments of the present application, a negative electrode tab includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer may be disposed on one surface of the negative electrode current collector in the thickness direction thereof, or may be disposed on both surfaces of the negative electrode current collector in the thickness direction thereof. The "surface" here may be the entire area of the surface of the negative electrode current collector or may be a partial area of the surface of the positive electrode current collector, and the present application is not particularly limited as long as the object of the present application can be achieved. The negative electrode current collector of the present application is not particularly limited as long as the object of the present application can be achieved, and for example, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, or a composite current collector (for example, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, or the like) may be included. The thickness of the anode material layer is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the anode material layer is 30 μm to 130 μm. The thickness of the negative electrode current collector is not particularly limited as long as the object of the present application can be achieved, for example, the negative electrode current collector has a thickness of 6 μm to 12 μm. The thickness of the negative electrode sheet is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the negative electrode sheet is 50 μm to 280 μm.

The anode material layer of the present application includes an anode active material, the anode active material layer may be one or more layers, and each of the multiple anode active material layers may contain the sameOr a different anode active material. The negative electrode active material is any substance capable of reversibly intercalating and deintercalating active ions such as lithium ions. The anode active material is not particularly limited as long as the object of the present application can be achieved, for example, the anode active material may contain, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon-carbon composite, li-Sn alloy, li-Sn-O alloy, sn, snO, snO ₂ Lithiated TiO of spinel structure ₂ -Li ₄ Ti ₅ O ₁₂ Or at least one of Li-Al alloys.

In the present application, the negative electrode material layer further includes a conductive agent and a binder, and the present application is not particularly limited in kind as long as the object of the present application can be achieved, and for example, at least one of the conductive agent and the binder may be used. The mass ratio of the anode active material, the conductive agent and the binder in the anode material layer is not particularly limited, and can be selected by a person skilled in the art according to actual needs as long as the purpose of the application can be achieved. The negative electrode material layer may further include a thickener, and the content and kind of the thickener are not particularly limited in the present application, and conventional kinds and contents known in the art may be employed as long as the object of the present application can be achieved.

Optionally, the negative electrode tab may further comprise a conductive layer located between the negative electrode current collector and the negative electrode material layer. The composition of the conductive layer is not particularly limited in the present application, and may be a conductive layer commonly used in the art. For example, the conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited, and may be at least one of the conductive agent and the binder, for example.

The material of the separator base material layer is not particularly limited as long as the object of the present application can be achieved. The substrate layer may be a nonwoven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. In the present application, the thickness of the base material layer is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the base material layer may be 1 μm to 50 μm; the thickness of the separator is not particularly limited as long as the object of the present application can be achieved, and for example, the thickness of the separator may be 5 μm to 100 μm.

Optionally, the separator may further include a surface treatment layer between the substrate layer and the adhesive layer. The composition of the surface treatment layer in the present application is not particularly limited, and the surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the present application is not particularly limited, and for example, may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder of the present application is not particularly limited, and may be at least one of the above binders, for example. The polymer layer contains a polymer, and the material of the polymer comprises at least one of polyamide, polyacrylonitrile, acrylic polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

The secondary battery of the present application further includes a pack for accommodating the positive electrode tab, the separator, the negative electrode tab, and the electrolyte, and other components known in the art of secondary batteries, and the present application is not limited thereto. The present application is not particularly limited, and may be any known in the art as long as the object of the present application can be achieved. For example, an aluminum plastic film package may be used.

The process of preparing the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited, and may include, for example, but not limited to, the following steps: sequentially stacking the positive electrode plate, the diaphragm and the negative electrode plate, winding and folding the positive electrode plate, the diaphragm and the negative electrode plate according to the need to obtain an electrode assembly with a winding structure, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag, and sealing to obtain a secondary battery; or sequentially stacking the positive electrode plate, the diaphragm and the negative electrode plate, fixing four corners of the whole lamination structure by using adhesive tapes to obtain an electrode assembly of the lamination structure, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag, and sealing to obtain the secondary battery. In addition, an overcurrent prevention element, a guide plate, or the like may be placed in the package bag as needed, thereby preventing the pressure inside the secondary battery from rising and overcharging and discharging.

The secondary battery of the present application may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, a lithium ion polymer secondary battery, or the like.

A second aspect of the present application provides an electronic device comprising the secondary battery provided in the first aspect of the present application. The electronic device provided by the application has good high-temperature circulation performance, high-temperature storage performance, high-temperature safety performance and low-temperature circulation performance, so that the electronic device provided by the application has good use performance. The kind of the electronic device is not particularly limited in the present application, and it may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-compact disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a power assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flash light, a camera, a household large-sized battery, a lithium ion capacitor, and the like.

The application has the beneficial effects that:

the application provides a secondary battery and an electronic device. The secondary battery comprises a positive electrode plate, a negative electrode plate, a diaphragm and electrolyte, wherein the electrolyte comprises a compound shown in a formula (I), the mass percentage of the compound shown in the formula (I) is x% which is more than or equal to 0.01 and less than or equal to 3, the diaphragm comprises a substrate layer and a bonding layer, the thickness of the bonding layer is h mu m, and x/h is more than or equal to 0.0004 and less than or equal to 0.6. The secondary battery comprises the diaphragm provided by the application, so that the transmission path of lithium ions can be shortened, and the transmission capacity of the lithium ions is improved, thereby improving the cycle performance of the secondary battery, but affecting the dissipation of interface heat between the diaphragm and the negative electrode plate, and further affecting the thermal stability of the negative electrode plate. The electrolyte comprising the compound shown in the formula (I) and the diaphragm are applied to the secondary battery, and the values of x and x/h are regulated and controlled within the range of the application, so that a solid electrolyte interface film with good thermal stability can be formed on the surface of the negative electrode plate, the thermal stability of the negative electrode plate is improved, and the cycle performance of the secondary battery is improved, and the high-temperature safety performance of the secondary battery is also improved.

Of course, it is not necessary for any one product or method of practicing the application to achieve all of the advantages set forth above at the same time.

Detailed Description

The following description of the technical solutions in the embodiments of the present application will be clear and complete, and it is obvious that the described embodiments are only some embodiments of the present application, but not all embodiments. All other embodiments obtained by the person skilled in the art based on the present application fall within the scope of protection of the present application.

In the specific embodiment of the present application, the present application is explained using a lithium ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium ion battery.

Examples

Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. The various tests and evaluations were carried out according to the following methods. Unless otherwise specified, "parts" and "%" are mass references.

Test method and apparatus:

and (3) hot box test:

the lithium ion battery is discharged to 3.0V at 25 ℃ under constant current of 0.5C, then is charged to 4.5V under constant current of 0.5C, and is charged to 0.05C under constant voltage of 4.5V. And (3) placing the lithium ion battery in a high-temperature furnace at 130 ℃, 132 ℃ or 134 ℃ for storage for 1 hour, and after the 1 hour is finished, observing whether the lithium ion battery catches fire or not, and judging that the lithium ion battery passes through the fire when the lithium ion battery catches fire is not caught.

And (3) high-temperature cycle test at 45 ℃):

and placing the lithium ion battery in a 45 ℃ incubator, and standing for 30 minutes to keep the lithium ion battery at a constant temperature. Charging the lithium ion battery with constant temperature to 4.5V at 45 ℃ under constant current of 0.2C, charging to 0.05C under constant voltage of 4.5V, standing for 5 minutes, discharging to 3.0V under constant current of 0.2C, standing for 5 minutes, and testing initial discharge capacity C of the lithium ion battery ₀ And an initial thickness H ₀ The method comprises the steps of carrying out a first treatment on the surface of the Then charging to 4.15V with a constant current of 1.3C, and charging to 1C with a constant voltage of 4.15V; then charging to 4.25V with 1C constant current, and then charging to 0.8C with 4.25V constant voltage; charging to 4.5V with constant current of 0.8C, and charging to 0.05C with constant voltage of 4.5V; standing for 5 minutes; then, the mixture was discharged to 3.0V at a constant current of 1C and allowed to stand for 5 minutes, which was a charge-discharge cycle. The discharge capacity C 'and the final thickness H' of the lithium ion battery after 400 cycles were tested according to the above charge/discharge cycle steps for 400 cycles.

Capacity retention after 400 cycles at 45 ℃ = C'/C ₀ ×100％。

Thickness expansion ratio after 400 circles of 45 ℃ circulation= (H' -H) ₀ )/H ₀ ×100％。

-10 ℃ low temperature cycle test:

and placing the lithium ion battery in a constant temperature box at the temperature of minus 10 ℃, and standing for 30 minutes to ensure that the lithium ion battery achieves constant temperature. Charging the constant-temperature lithium ion battery to 4.5V at-10deg.C under constant current of 0.2C, charging to 0.05C under constant voltage of 4.5V, standing for 5 min, discharging to 3.0V under constant current of 0.2C, standing for 5 min, and testing initial capacity C ₁₁ The method comprises the steps of carrying out a first treatment on the surface of the Then charging to 4.2V with constant current of 0.5C, and charging to 0.3C with constant voltage of 4.2V; charging to 4.5V with constant current of 0.3C, and charging to 0.05C with constant voltage of 4.5V; standing for 5 minutes; then discharging to 3.0V at constant current of 0.2C, and standing for 5 minutes; this is a charge-discharge cycle. Cycling according to the charge/discharge cycling steps200 circles, and testing discharge capacity C of lithium ion battery after 200 circles of circulation ₁₂ And calculating the capacity retention rate of the lithium ion battery after 200 cycles.

Capacity retention after 200 cycles at-10 ℃ = C ₁₂ /C ₁₁ ×100％。

-10 ℃ discharge capacity ratio test:

standing the lithium ion battery in a constant temperature box at 25 ℃ for 1 hour to keep the lithium ion battery constant temperature; charging to 4.2V with 0.5C constant current, charging to 4.5V with 0.3C constant current, charging to 0.02C with 4.5V constant voltage, and standing for 30 min; then discharging to 3.4V with constant current of 0.2C, standing for 30 min, and discharging to obtain the final product (D ₀ ) As a reference. Charging to 4.2V at 25deg.C under constant current of 0.5C, charging to 4.5V under constant current of 0.3C, charging to 0.02C under constant voltage of 4.5V, and standing for 30 min; the temperature in the incubator is adjusted to be minus 10 ℃, and the lithium ion battery is kept stand in the incubator at minus 10 ℃ for 1 hour, so that the lithium ion battery is kept at a constant temperature; discharging to 3.4V with constant current of 0.2C, recording the capacity at this time as D ₁ . -10 ℃ discharge capacity ratio = D ₁ /D ₀ ×100％。

Testing of adhesion:

the secondary battery is disassembled to obtain a diaphragm, a positive electrode plate and a negative electrode plate, the diaphragm and the positive electrode plate are cut into samples with the thickness of 54.2mm multiplied by 72.5mm, the diaphragm and the positive electrode/negative electrode are compounded, a hot press is used for hot pressing, the hot pressing condition is 85 ℃, 1Mpa and 85s, the compounded samples are cut into strips with the thickness of 15mm multiplied by 54.2mm, the cut samples are adhered to a flat glass plate, one end of the diaphragm is clamped on a clamp and is peeled by constant force, and corresponding adhesive force is displayed in a corresponding peeling instrument (the adhesive force is tested at normal temperature (25 ℃) according to 180 DEG peel strength testing standard).

Particle size testing:

a50 ml clean beaker was filled with a powder sample of approximately 0.02g of the positive electrode material, 20ml of deionized water was added, and then surfactant was added dropwise to completely disperse the powder in water, sonicated in a 120W sonicator for 5min, and then the particle size distribution was tested by a laser particle size tester (MasterSizer 2000). In the volume-based particle size distribution of the material, the particle diameter reaching 50% by volume accumulation is Dv50, and the particle diameter reaching 99% by volume accumulation is Dv99, as measured from the small particle diameter.

Example 1-1

< preparation of Positive electrode sheet >

Mixing positive electrode material lithium cobaltate, conductive agent acetylene black and binder polyvinylidene fluoride according to the mass ratio of 96:2:2, adding N-methyl pyrrolidone (NMP), and uniformly stirring under the action of a vacuum stirrer to obtain positive electrode slurry, wherein the solid content of the positive electrode slurry is 70wt%. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil having a thickness of 12 μm, and the aluminum foil was baked at 120 ℃ for 1 hour to obtain a positive electrode sheet having a single surface coated with a positive electrode material layer having a thickness of 100 μm. Repeating the steps on the other surface of the aluminum foil to obtain the positive electrode plate with the double-sided coating positive electrode material layer. Drying for 1 hour under the vacuum condition of 120 ℃, and then carrying out cold pressing, cutting and slitting to obtain the positive pole piece with the specification of 74mm multiplied by 867 mm. Wherein, the Dv50 of the positive electrode material lithium cobaltate is 12 mu m, and the Dv99 is 24 mu m.

< preparation of negative electrode sheet >

Mixing negative electrode active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethylcellulose (CMC) according to the mass ratio of 95:2:2:1, adding deionized water, and uniformly stirring under the action of a vacuum stirrer to obtain negative electrode slurry, wherein the solid content of the negative electrode slurry is 75wt%. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with the thickness of 12 mu m, and the copper foil is dried at 120 ℃ to obtain a negative electrode plate with the coating thickness of 130 mu m and a negative electrode material layer coated on one side. Repeating the steps on the other surface of the copper foil to obtain the negative electrode plate with the double-sided coating negative electrode material layer. Drying for 1 hour under the vacuum condition of 120 ℃, and then carrying out cold pressing, cutting and slitting to obtain the negative electrode plate with the specification of 74mm multiplied by 867 mm.

< preparation of electrolyte >

In an argon atmosphere glove box with the water content of less than 10ppm, mixing the non-aqueous organic solvents of ethylene carbonate and diethyl carbonate according to the mass ratio of 3:7, and thenThen adding lithium hexafluorophosphate (LiPF) as lithium salt into the non-aqueous organic solvent ₆ ) The compound shown in the formula (I) is shown in the formula (I-1) to obtain the electrolyte. Based on the mass of the electrolyte, lithium salt LiPF ₆ The mass percentage of the compound shown in the formula (I) is 12 percent, the mass percentage x% of the compound shown in the formula (I-1) is 0.5 percent, and the rest is non-aqueous organic solvent.

< preparation of separator >

A porous polyethylene film (supplied by Celgard corporation) having a thickness of 5 μm was used as the separator substrate.

Preparation of the first adhesive layer:

the first binder ethylene-propylene-maleic anhydride copolymer and methylcyclohexane solution (methylcyclohexane is dissolved in water, mass percentage is 15%) were fed into a reaction kettle (with a water separator) according to a weight ratio of 3:7, stirred at 130 ℃ for 4 hours, and rotational speed is 50rpm, to obtain a first solution. N-dodecyl dimethylamine, hexadecyl trimethyl ammonium bromide and deionized water are mixed according to the weight ratio of 3:4:3, and stirred for 30min at room temperature at the rotating speed of 50rpm, so as to obtain a second solution. Mixing the first solution and the second solution according to a weight ratio of 1:1, stirring for 5min at room temperature at a rotating speed of 1000rpm to obtain a primary emulsion solution; delivering the colostrum solution into a homogenizer, homogenizing under 500bar pressure to obtain polymer. Wherein the ethylene-propylene-maleic anhydride copolymer is a copolymer obtained by copolymerizing 10% by mass of ethylene, 85% by mass of propylene and 5% by mass of maleic anhydride, and has a weight average molecular weight of 300000 to 800000.

Adding the polymer into a stirrer, and uniformly stirring; adding sodium carboxymethyl cellulose into the slurry, and uniformly stirring; adding polyoxyethylene ether; and finally, adding deionized water, and adjusting the viscosity of the first adhesive layer slurry to 40 mPa.s and the solid content to 5% to obtain the first adhesive layer slurry. The first adhesive layer slurry is uniformly coated on the surface of the diaphragm substrate, which is opposite to the positive electrode, and the surface is dried by an oven, wherein the coating thickness of the first adhesive layer is 15 mu m.

Preparation of the second adhesive layer:

91g of a second binder of styrene-butyl acrylate-methyl acrylate copolymer is added into a stirrer, 0.5g of sodium carboxymethyl cellulose is added, and the mixture is stirred and mixed uniformly; adding 8.5g of wetting agent dimethyl siloxane, and then adding deionized water to stir, and adjusting the viscosity of the second adhesive layer slurry to 40 mPa.s and the solid content to 5%; the second adhesive layer paste was uniformly coated on the surface of the separator substrate facing the negative electrode, and dried in an oven, and the second adhesive layer coating thickness was 2 μm. Wherein the styrene-butyl acrylate-methyl acrylate copolymer is a copolymer formed by copolymerizing 60% by mass of styrene, 20% by mass of butyl acrylate and 20% by mass of methyl acrylate, and has a weight average molecular weight of 300000-800000 and a Dv50 of 0.6 mu m.

< preparation of lithium ion Battery >

And sequentially stacking the prepared positive electrode plate, the diaphragm and the negative electrode plate, so that the diaphragm is positioned between the positive electrode plate and the negative electrode plate to play a role in isolation, and winding to obtain the electrode assembly. And (3) placing the electrode assembly in an aluminum plastic film packaging bag after welding the electrode lugs, drying, injecting electrolyte, and carrying out vacuum packaging, standing, formation (the upper limit voltage of formation is 4.5V, the formation temperature is 70 ℃ and the formation standing time is 2 hours), degassing, trimming and other working procedures to obtain the lithium ion battery.

Examples 1-2 to 1-31

The procedure of example 1-1 was repeated except that the compound of formula (I) and the mass percentages thereof, the first adhesive layer thickness and the second adhesive layer thickness were adjusted as shown in Table 1. Wherein, when the mass percentage of the compound shown in the formula (I) is changed, the mass percentage of the nonaqueous organic solvent is changed, and the mass percentage of the lithium salt is unchanged.

Examples 2-1 to 2-4

The procedure of example 1-1 was repeated except that the first binder type and the second binder type were adjusted as shown in Table 2 in < preparation of separator >.

Examples 3-1 to 3-7

The procedure of example 1-1 was repeated except that the carboxylic acid ester compound was added as shown in Table 3 and the kind and mass percentage thereof were adjusted as shown in Table 3 in < preparation of electrolyte >. Wherein, when the mass percentage of the carboxylate compound is changed, the mass percentage of the nonaqueous organic solvent is changed, and the mass percentage of the lithium salt is unchanged.

Examples 4-1 to 4-9

The procedure of example 1-1 was repeated except that the compound of the formula (II) was added as shown in Table 4 and the kind and mass percentage thereof were adjusted as shown in Table 4 in < preparation of electrolyte >. Wherein, when the mass percentage of the compound of the formula (II) is changed, the mass percentage of the nonaqueous organic solvent is changed, and the mass percentage of the lithium salt is unchanged.

Example 5-1

< preparation of Positive electrode sheet >

Sintering the mixture containing the precursor material at 900 ℃ to obtain the primary positive electrode active material LiCoO ₂ The method comprises the steps of carrying out a first treatment on the surface of the Mixing the primary positive electrode active material with a compound containing M element according to a molar ratio of 95:5, and sintering at 800 ℃ to obtain the positive electrode material. Wherein the mixture of the precursor materials is Co ₃ O ₄ And Li (lithium) ₂ CO ₃ Mixing according to a molar ratio of 1:1.05 to obtain the compound containing M element which is Al ₂ O ₃ 。

The procedure of example 1-1 was repeated except that the above-mentioned positive electrode material was used in place of the lithium cobaltate of example 1-1.

< preparation of negative electrode sheet >, < preparation of electrolyte >, < preparation of separator >, < preparation of lithium ion battery > are the same as in example 1-1.

Examples 5-2 to 5-12

The procedure of example 5-1 was repeated except that in < preparation of positive electrode sheet > compounds containing different elements were used as shown in Table 5, and the mass percentage of element M contained in the positive electrode material was controlled by adjusting the molar ratio of the primary positive electrode active material to the compound containing element M.

Examples 6-1 to 6-10

The procedure of example 1-1 was repeated except that the relevant production parameters were adjusted in accordance with Table 6 in < production of positive electrode sheet >.

Example 7-1

The procedure of example 1-1 was repeated except that propyl propionate, a compound of formula (II), and 1, 4-butane sultone were added to the electrolyte solution and the mass percentage of the nonaqueous organic solvent was changed and the mass percentage of the lithium salt was not changed as shown in Table 7.

Examples 7-2 to 7-4

Examples 5 to 3 were the same except that in < preparation of electrolyte > the carboxylate compound propyl propionate and/or the compound 1, 4-butane sultone of formula (II) was added as shown in table 7, and the mass percentage of the nonaqueous organic solvent was changed and the mass percentage of the lithium salt was unchanged as shown in table 7.

Comparative examples 1 to 1

The procedure of example 1-1 was repeated except that the compound represented by the formula (I) was not added to the solution for the preparation of the electrolyte, the mass percentage of the nonaqueous organic solvent was changed, and the mass percentage of the lithium salt was not changed, and only a porous polyethylene film having a thickness of 5 μm was used as the separator for the solution for the preparation of the separator, and the first adhesive layer and the second adhesive layer were not prepared.

Comparative examples 1 to 2

The procedure of example 1-1 was repeated except that in the < preparation of separator > only a porous polyethylene film having a thickness of 5 μm was used as a separator, and the first adhesive layer and the second adhesive layer were not prepared.

Comparative examples 1 to 3

The procedure of example 1-1 was repeated, except that the compound of the formula (I) was not added to the solution < preparation of electrolyte >, the mass percentage of the nonaqueous organic solvent was changed, and the mass percentage of the lithium salt was not changed.

Comparative examples 1 to 4 to 1 to 5

The procedure of example 1-1 was repeated, except that the mass percentage of the compound represented by the formula (I) was changed as shown in Table 1, and the mass percentage of the nonaqueous organic solvent and the mass percentage of the lithium salt were not changed.

TABLE 1

/>

Note that: the "/" in Table 1 indicates that no corresponding substance or parameter is present.

The lithium ion batteries of example 1-1 have significantly improved high temperature cycle performance, low temperature cycle performance, high temperature safety performance, low temperature discharge performance, and low temperature cycle performance as compared to comparative examples 1-1 to 1-3.

As can be seen from examples 1 to 7, comparative examples 1 to 4 to comparative examples 1 to 5, when x is too small, for example, comparative examples 1 to 4, the high-temperature safety performance and the high-temperature storage performance of the lithium ion battery are poor; when the value of x is too large, for example, comparative examples 1 to 5, the high-temperature cycle performance, the low-temperature cycle performance, and the low discharge performance of the lithium ion battery are poor; the x value is too large or too small, and the high-temperature cycle performance, the high-temperature storage performance and the high-temperature safety performance of the lithium ion battery, as well as the low-temperature discharge performance and the low-temperature cycle performance cannot be considered. When x is more than or equal to 0.01 and less than or equal to 3, the lithium ion battery has higher 45 ℃ cycle capacity retention rate, lower 45 ℃ thickness expansion rate, higher hot box test passing rate and higher-10 ℃ discharge capacity ratio and capacity retention rate, so that the value of x is regulated and controlled to be within the range of the application, and the lithium ion battery has good high-temperature cycle performance, high-temperature storage performance, high-temperature safety performance, low-temperature discharge performance and low-temperature cycle performance. It can be seen from examples 1-1 to 1-7, examples 1-11, examples 1-15 to examples 1-23 that the lithium ion battery has good high temperature cycle performance, high temperature storage performance, high temperature safety performance, low temperature discharge performance and low temperature cycle performance when x/h satisfies 0.0004.ltoreq.x/h.ltoreq.0.6.

As can be seen from examples 1-1 to 1-31, comparative examples 1-1 to 1-5, the electrolyte including the compound represented by formula (I) within the scope of the present application and the separator of the present application were applied to lithium ion batteries while adjusting the values of x, x/h within the scope of the present application, the resulting lithium ion batteries had higher 45 ℃ cycle capacity retention, lower 45 ℃ thickness expansion rate, higher hot box test pass rate, higher-10 ℃ discharge capacity ratio and higher-10 ℃ cycle capacity retention rate, thereby demonstrating that the lithium ion batteries had better high temperature cycle performance, high temperature storage performance, high temperature safety performance, low temperature discharge performance and low temperature cycle performance.

It can be seen from examples 1-1 to 1-31 that the low temperature cycle performance, the low temperature discharge performance, the high temperature cycle performance and the high temperature safety performance of the lithium ion battery can be improved when the value of the bonding layer thickness h is regulated within the range of 5 to 25. When the thickness h of the bonding layer is regulated to be within the range of 6-20, the low-temperature cycle performance, the low-temperature discharge performance, the high-temperature cycle performance and the high-temperature safety performance of the lithium ion battery can be further improved.

From examples 1-8 to examples 1-14, it can be seen that the lithium ion battery has superior high temperature cycle performance, high temperature storage performance, high temperature safety performance, low temperature discharge performance and low temperature cycle performance when the adhesion between the separator and the negative electrode sheet is in the range of 3N/m to 29N/m. When the bonding force between the diaphragm and the negative electrode plate is in the range of 5N/m to 28N/m, the lithium ion battery has better high-temperature cycle performance, high-temperature storage performance, high-temperature safety performance, low-temperature discharge performance and low-temperature cycle performance.

From examples 1-1 to 1-31, it can be seen that adjusting the thickness of the first adhesive layer of the separator to be in the range of 5 μm to 20 μm and the thickness of the second adhesive layer to be in the range of 0.2 μm to 4 μm is beneficial to improving the 45 ℃ cycle capacity retention rate, -10 ℃ discharge capacity ratio and-10 ℃ cycle capacity retention rate of the lithium ion battery, and reducing the 45 ℃ thickness expansion rate, which means that adjusting the thickness of the first adhesive layer and the thickness of the second adhesive layer of the separator to be in the above ranges is beneficial to improving the low temperature performance, the high temperature cycle performance and the high temperature safety performance of the lithium ion battery.

TABLE 2

As can be seen from table 2 examples 1-1, 2-1 to 2-4, when the separator using the first binder type and the second binder type within the scope of the present application is applied to a lithium ion battery, the lithium ion battery has superior high temperature cycle performance, high temperature storage performance, high temperature safety performance, low temperature discharge performance, and low temperature cycle performance.

TABLE 3 Table 3

Note that: the "/" in Table 3 indicates that no corresponding substance or parameter is present.

As can be seen from table 3, examples 1-1, 3-1 to 3-7, when the solvent of the carboxylate compound is further added on the basis of the electrolyte in example 1-1, the high temperature cycle performance, the high temperature safety performance, the low temperature discharge performance and the low temperature cycle performance are further improved, and the lithium ion battery has better high temperature performance and low temperature performance; along with the increase of the dosage of the carboxylic ester compound, the high-temperature cycle performance, the low-temperature discharge performance and the low-temperature cycle performance of the lithium ion battery tend to be improved and then reduced; in conclusion, in the lithium ion battery further adopting the carboxylate compound in the content range of the application, the high-temperature cycle performance, the high-temperature safety performance, the low-temperature discharge performance and the low-temperature cycle performance can be further improved.

TABLE 4 Table 4

Note that: the "/" in Table 4 indicates that no corresponding substance or parameter is present.

As can be seen from examples 4-1 to 4-7 of Table 4, as the content of the compound of formula (II) increases, the high temperature safety performance of the lithium ion battery is improved, and the high temperature cycle performance, the high temperature storage performance, the low temperature discharge performance and the low temperature cycle performance all tend to be improved and then reduced. It can be seen from examples 1-1, 4-1 to 4-9 that when the mass percentage content a and the kind of the compound of formula (II) are within the scope of the present application, the obtained lithium ion battery has good low temperature performance, high temperature cycle performance and safety performance. It can be seen from examples 4-3, 4-7 to 4-8 that when the compound of formula (II-1) and the compound of formula (II-2) of the present application are used together and the mass percentage a of the compound of formula (II) is regulated to be within the scope of the present application, the obtained lithium ion battery has good high temperature safety performance and better low temperature performance and high temperature cycle performance.

TABLE 5

Note that: the "/" in Table 5 indicates that no corresponding substance or parameter is present.

As can be seen from examples 1-1, 5-1 to 5-12, when the positive electrode material contains at least one of Al, mg, zr, ti or La elements and the content of M element is regulated to be in the range of 0.01% to 3%, the capacity retention rate of the lithium ion battery after 400 cycles at 45 ℃ can be further improved, -the discharge capacity ratio at 10 ℃ and the capacity retention rate of the lithium ion battery after 200 cycles at 10 ℃ can be further increased, the thickness expansion rate after 400 cycles at 45 ℃ can be reduced, i.e. the low-temperature discharge performance, the low-temperature cycle performance, the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery can be further improved by introducing M element in the category and the content range of the positive electrode material.

TABLE 6

As can be seen from examples 6-1 to 6-10, when the positive electrode material satisfies the particle, dv50 is in the range of 10 μm to 15 μm; or the Dv99 of the particles is in the range of 20 μm to 45 μm; or when the Dv99/Dv50 is in the range of 1.5 to 4.5, the capacity retention rate of the lithium ion battery in a low-temperature environment and the capacity retention rate of the lithium ion battery in a 45 ℃ environment can be improved, namely the low-temperature cycle performance and the high-temperature cycle performance of the lithium ion battery are improved. When at least two of Dv50 of 10 μm to 15 μm, dv99 of 20 μm to 45 μm and Dv99/Dv50 of 1.5.ltoreq.Dv99.ltoreq.4.5 are satisfied, the low temperature cycle performance and the high temperature cycle performance of the lithium ion battery are further improved while good high temperature safety performance is provided. When the Dv50 is 10 mu m to 15 mu m, the Dv99 is 20 mu m to 45 mu m, and the Dv99/Dv50 is not more than 1.5 and not more than 4.5, the low-temperature cycle performance and the high-temperature cycle performance of the lithium ion battery are further improved while the high-temperature safety performance is good.

TABLE 7

Note that: the "/" in Table 7 indicates that no corresponding substance or parameter is present.

As can be seen from examples 1-1, 5-3, and 7-1 to 7-4, when the lithium ion battery further comprises at least two of a carboxylate compound, a compound of formula (ii), and a positive electrode material containing M element on the basis of an electrolyte comprising a compound of formula (I) and a separator comprising a substrate layer and a binder layer, the capacity retention rate after 400 cycles at 45 c, -a 10 c discharge capacity ratio, -a capacity retention rate after 200 cycles at 10 c, the thickness expansion rate after 400 cycles at 45 c is reduced, and the number of passes of 134 c hot boxes is increased, i.e., the introduction of at least two of a carboxylate compound, a compound of formula (ii), and a positive electrode material containing M element can further improve the low-temperature cycle performance, low-temperature discharge performance, high-temperature cycle performance, high-temperature storage performance, and high-temperature safety performance of the lithium ion battery. Meanwhile, when the carboxylate compound, the compound shown in the formula (II) and the positive electrode material containing the M element are adopted, the low-temperature cycle performance, the low-temperature discharge performance, the high-temperature cycle performance, the high-temperature storage performance and the high-temperature safety performance of the lithium ion battery can be further improved.

The foregoing description of the preferred embodiments of the application is not intended to limit the application to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the application are intended to be included within the scope of the application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte comprising a compound represented by formula (I):

wherein R is ₁ Selected from O or-CH (Ra) -, ra is selected from H, F, C ₁ To C ₅ Alkyl or C of (2) ₁ To C ₅ Alkoxy groups of (a); r is R ₂ And R is ₃ Each independently selected from H, F, C ₁ To C ₅ Alkyl, C of (2) ₁ To C ₅ Alkoxy or C of (2) ₂ To C ₅ Alkenyl, C ₂ To C ₅ Alkynyl of (a); r is R ₄ Independently selected from H, F, C unsubstituted or substituted with F ₁ To C ₅ Alkyl, C of (2) ₁ To C ₅ Alkoxy, C ₂ To C ₅ Alkenyl or C of (2) ₂ To C ₅ Alkynyl of (a);

based on the mass of the electrolyte, the mass percentage of the compound shown in the formula (I) is x%, and x is more than or equal to 0.01 and less than or equal to 3;

the diaphragm comprises a substrate layer and a bonding layer, wherein the thickness of the bonding layer is h mu m, and x/h is more than or equal to 0.0004 and less than or equal to 0.6.

2. The secondary battery according to claim 1, wherein the compound represented by formula (I) comprises at least one of the following compounds:

3. the secondary battery according to claim 1, wherein the secondary battery satisfies at least one of:

a.0.1≤x≤2.5，

H is more than or equal to 5 and less than or equal to 25, preferably is more than or equal to 6 and less than or equal to 20,

c.0.005≤x/h≤0.4。

4. the secondary battery according to claim 1, which satisfies at least one of the following features:

(1) The bonding force between the diaphragm and the negative electrode plate is 3N/m to 29N/m;

(2) The adhesive layer includes a first adhesive layer including a first adhesive including at least one of vinylidene fluoride, hexafluoropropylene, or an ethylene-propylene-maleic anhydride copolymer; wherein the mass ratio of ethylene, propylene and maleic anhydride in the ethylene-propylene-maleic anhydride copolymer is (5 to 15): (70 to 95): (3 to 8);

(3) The adhesive layer comprises a second adhesive layer comprising a second adhesive comprising at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate or styrene-butyl acrylate-methyl acrylate copolymer, wherein the mass ratio of styrene, butyl acrylate to methyl acrylate in the styrene-butyl acrylate-methyl acrylate copolymer is (50 to 70): 10 to 30;

(4) The adhesive layer includes a first adhesive layer having a thickness of 5 μm to 20 μm and a second adhesive layer having a thickness of 0.2 μm to 4 μm.

5. The secondary battery according to claim 1, wherein the electrolyte further comprises a carboxylate compound including at least one of propyl propionate, ethyl acetate, methyl pivalate, methyl valerate, 2-difluoroethyl propionate, or 2, 2-difluoroethyl acetate;

based on the mass of the electrolyte, the mass percentage of the carboxylate compound is y.25-72.

6. The secondary battery according to claim 1, wherein the electrolyte further comprises a compound of formula (II) comprising at least one of a compound of formula (II-1) or a compound of formula (II-2),

wherein R is ₂₁ And R is ₂₂ Each independently selected from H, C ₁ To C ₄ N is 1 or 2; d and E are each independently selected from C ₁ To C ₈ An alkylene group of (a);

based on the mass of the electrolyte, the mass percentage of the compound of the formula (II) is a percent, and a is more than or equal to 0.2 and less than or equal to 5.

7. The secondary battery according to claim 6, which satisfies at least one of the following features:

(1) The compound represented by the formula (II-1) contains at least one of 1, 3-propane sultone, 1, 4-butane sultone, 5-methyl oxathiapent-2, 2-dioxide and 2, 4-butane sultone;

(2) The compound represented by the formula (II-2) contains at least one of methylene methane disulfonate or ethylene methane disulfonate.

8. The secondary battery according to claim 1, wherein the positive electrode sheet includes a positive electrode material including an element M including at least one of Al, mg, zr, ti or La elements, the element M being 0.01.ltoreq.b.ltoreq.3 by mass based on the mass of the positive electrode material.

9. The secondary battery according to any one of claims 1 to 8, wherein the positive electrode sheet includes a positive electrode material that satisfies at least one of the following characteristics:

(1) The particle diameter Dv50 of the positive electrode material is 10 μm to 15 μm;

(2) The particle diameter Dv99 of the positive electrode material is 20 μm to 45 μm;

(3) The particle sizes Dv50 and Dv99 of the positive electrode material satisfy the following conditions: dv99/Dv50 is less than or equal to 1.5 and less than or equal to 4.5.

10. An electronic device comprising the secondary battery according to any one of claims 1 to 9.