battery

Abstract

The application relates to the field of batteries, and provides a battery, which comprises a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte; the diaphragm comprises a base film and polymer layers located on both sides of the base film; monomers of the polymer layers comprise first monomers and second monomers, the first monomers are selected from acrylate monomers, and the second monomers are ene nitrile monomers; the electrolyte comprises a first additive; the battery satisfies a relationship formula: A1 / S<100, wherein A1 is the content of the first additive in the electrolyte, and the unit is wt%; S is the proportion of the covering area of the single-side polymer layer to the area of the single-side diaphragm, and the unit is %, and S<100. By simultaneously improving the diaphragm and the electrolyte additive in the battery, the thermal stability of the battery is effectively improved, and the battery also has good electrical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, and in particular to a battery. BACKGROUND

[0002] Lithium ion batteries, as energy storage devices with good comprehensive performance in energy density, cycle life, rate charge and discharge, environmental friendliness, etc., have been widely used in various aspects of life. A lithium ion battery is usually composed of a positive electrode, a negative electrode, a separator, an electrolyte and a packaging material. Since most of the currently commercialized lithium ion batteries use organic solvent prepared electrolyte with relatively low boiling point and flammability, the use of organic electrolyte makes the lithium ion battery have the risk of thermal expansion and even explosion and fire, and the thermal stability of SEI generated by the reduction and decomposition of electrolyte is poor. In addition, the thermal decomposition of the positive electrode material or the catalytic decomposition of the electrolyte also easily leads to the problem of battery thermal gas production. Therefore, the thermal safety performance of lithium ion batteries has attracted widespread attention, and further improvement of the electrolyte of lithium ion batteries and the solid electrolyte film (SEI) formed therefrom is needed. For example, CN116454393A proposes that the high-temperature stability of the battery can be improved by controlling the content of lithium nitride and substances containing silicon-carbon bonds in the SEI.

[0003] In addition, as a key component for isolating positive and negative electrode materials to prevent short circuit of the battery, the separator has an important influence on the thermal safety performance and rate of lithium ion batteries. CN115312978A improves the closed-pore-to-broken-film interval of the separator by coating with an organic polymer, thereby improving the ability of the battery to resist thermal runaway. However, the current separator material still faces problems such as poor liquid retention, poor contact effect with positive and negative electrode materials, or poor kinetics.

[0004] Modification of the separator and adjustment of the electrolyte are important ways to improve the thermal safety and stability of lithium ion batteries, and the current conventional method is usually difficult to balance the thermal safety and electrochemical performance, therefore, it is necessary to develop a battery that can balance the thermal safety and electrical performance. SUMMARY

[0005] The purpose of the present application is to overcome the above-mentioned problems existing in the prior art, and to provide a battery. In the present application, the separator and the electrolyte additive in the battery are improved synchronously, thereby effectively improving the thermal stability of the battery, and also making the battery have good electrochemical performance.

[0006] In order to achieve the above-mentioned purpose, the present application provides a battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the separator comprises a base film and a polymer layer located on both sides of the base film;

[0007] The monomer of the polymer layer comprises a first monomer and a second monomer, the first monomer is selected from acrylate monomers, and the second monomer is an ene nitrile monomer.

[0008] The electrolyte comprises a first additive having a structure shown in Formula I:

[0009]

[0010] wherein R1, R2 and R3 are each independently H, methyl or halogen; R4 is absent or R4 is substituted or unsubstituted C1-C6 alkyl or substituted or unsubstituted C1-C6 alkoxy; R5, R6 and R7 are each independently selected from substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted amine group or substituted or unsubstituted amide group, and each substituent is independently C1-C2 alkyl, C1-C2 haloalkyl or halogen;

[0011] The battery satisfies the relationship:

[0012] wherein A1 is the content of the first additive in the electrolyte, in wt%; S is the proportion of the covering area of the single-sided polymer layer to the single-sided separator area, in %, and S < 100.

[0013] Preferably, the electrolyte further comprises a second additive and a third additive, the second additive is a fluorinated solvent, and the third additive is a sulfur-containing compound.

[0014] Preferably, the coating method of the polymer layer is dot matrix coating.

[0015] The application has the following beneficial effects by adopting the above technical solution:

[0016] (1) The application improves the separator and the electrolyte additive in the lithium ion battery simultaneously, and when the content of the first additive in the electrolyte and the proportion of the covering area of the single-sided polymer layer to the single-sided separator area satisfy the above relationship, the thermal stability of the battery is effectively improved, the battery has good thermal oven test passing rate, and the battery also has good electrochemical performance.

[0017] (2) In the separator, a slightly swellable polymer layer is coated on both sides of the base film, the interaction between the polymer layer and the electrolyte improves the liquid retention of the separator, which is beneficial to improving the cycle life of the battery, and the interaction between the functional groups in the polymer and the components of the electrolyte is beneficial to improving the stability of the electrolyte and delaying the time of thermal failure. In addition, the addition of cyano groups in the polymer can effectively block the free metal ions from reaching the negative electrode, and reduce the risk of heterogeneous metal catalytic SEI and decomposition of the electrolyte at the negative electrode.

[0018] (3) In the electrolyte component, the first additive with the structure shown in formula I is used, preferably in combination with the second additive and the third additive, so that the formed SEI is rich in inorganic components such as lithium silicate, lithium sulfate, lithium sulfite or lithium fluoride, and organic components such as silane or siloxane, thereby reducing the risk of SEI gas production; at the same time, these mixed inorganic lithium salts can assist the transmission of lithium ions and inhibit the volume expansion of the negative electrode material, so that the cycle stability and interface impedance of the battery are taken into account. The synergistic effect of the heat-resistant SEI and the separator with good liquid retention can effectively improve the thermal safety of the lithium ion battery.

[0019] (4) Under the preferred condition, the non-full-coverage dot matrix coating technology is used, and the non-coating area can be used as a channel for rapid migration of lithium ions, which takes into account the rate performance of the lithium ion battery.

[0020] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the invention. Any numerical value, however, can include values up to and including the value of the lower limit, and values up to and including the value of the upper limit, as if such limits were expressly written herein. Any numerical range recited herein is intended to include all sub-ranges subsumed therein. For ranges containing endpoints, names of individual points distributed along the range are also included. In this disclosure and during the administration of this application, the use of "or" means "and / or" unless specifically stated otherwise. In addition, it is specifically intended that the description used herein includes all grammatical and statistical equivalents of the terms unless otherwise indicated by context. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The schematic diagram of the coated area and the non-coated area of the polymer layer in the separator is shown; wherein 1 is the cross-sectional schematic position in the separator, 2 is the coated area of the polymer layer, and 3 is the non-coated area of the polymer layer. Figure 2

[0022] Figure 2 The schematic diagram of a cross section of a separator is shown; wherein 11 is the base film, 12 is the heat-resistant layer, and 13 is the polymer layer. DETAILED DESCRIPTION

[0023] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present application, and are not intended to limit the present application.

[0024] Unless otherwise defined, all scientific and technical terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0025] The present application provides a battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the separator comprises a base film and a polymer layer on both sides of the base film;

[0026] ​The monomers of the polymer layer comprise a first monomer selected from acrylate monomers and a second monomer which is an acrylonitrile monomer;

[0027] The electrolyte comprises a first additive having a structure shown in Formula I:

[0028]

[0029] wherein R1, R2, and R3 are each independently H, methyl, or halogen; R4 is absent or R4 is a substituted or unsubstituted C1-C6 alkyl or a substituted or unsubstituted C1-C6 alkoxy; R5, R6, and R7 are each independently selected from a substituted or unsubstituted C1-C6 alkyl, a substituted or unsubstituted C1-C6 alkoxy, a substituted or unsubstituted amine group, or a substituted or unsubstituted amide group, and each substituent is independently a C1-C2 alkyl, a C1-C2 haloalkyl, or a halogen;

[0030] The battery satisfies the relationship:

[0031] wherein A1 is the content of the first additive in the electrolyte, in wt%; S is the ratio of the coverage area of the single-sided polymer layer to the area of the single-sided separator, in %, and S < 100.

[0032] In some embodiments, the acrylate monomers include, but are not limited to, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, butyl trifluoromethacrylate, and the like.

[0033] In some embodiments, the first monomer is selected from at least one of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, and butyl trifluoromethacrylate. The first monomer mainly affects the liquid absorption of the separator and the polymer layer adhesion.

[0034] In some embodiments, the second monomer is selected from at least one of acrylonitrile, butenitrile, 2-methyl-3-butenitrile, and methacrylonitrile. At high temperatures, metal ions (such as cobalt ions) of the lithium ion battery cathode are dissolved and enter the electrolyte. The cyano group in the second monomer can effectively block the metal ions dissolved from the cathode from migrating to the anode, and inhibit the catalytic decomposition of the SEI by the metal or metal ions.

[0035] In some embodiments, the monomers of the polymer layer further comprise a third monomer selected from at least one of an acrylic monomer, an acrylamide monomer, a styrene monomer, and an anhydride monomer. The third monomer can be used to assist in adjusting the liquid absorption and mechanical properties of the polymer layer.

[0036] In some embodiments, the acrylic monomer includes, but is not limited to, acrylic acid, methacrylic acid, acrylic acid salt (such as sodium acrylate, aluminum acrylate, etc.), a-phenyl acrylic acid, etc.

[0037] In some embodiments, the acrylamide monomer includes, but is not limited to, acrylamide, methacrylamide, N-isopropyl acrylamide, N,N-dimethyl acrylamide, etc.

[0038] In some embodiments, the styrene monomer includes, but is not limited to, styrene, methylstyrene, fluorostyrene, etc.

[0039] In some embodiments, the anhydride monomer includes, but is not limited to, maleic anhydride, trifluoromethyl maleic anhydride, methyl maleic anhydride, phenyl maleic anhydride, etc.

[0040] In some embodiments, the third monomer is selected from at least one of acrylic acid, methacrylic acid, acrylic acid salt, a-phenyl acrylic acid, acrylamide, methacrylamide, N-isopropyl acrylamide, N,N-dimethyl acrylamide, styrene, methylstyrene, fluorostyrene, maleic anhydride, trifluoromethyl maleic anhydride, methyl maleic anhydride, phenyl maleic anhydride.

[0041] In some embodiments, the monomers of the polymer layer include the first monomer in a proportion of 40wt%-100wt%, for example, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, or 100wt%, the second monomer in a proportion of 5wt%-40wt%, for example, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, or 40wt%, and the third monomer in a proportion of 0wt%-20wt%, for example, 0wt%, 1wt%, 5wt%, 10wt%, 15wt%, or 20wt%.

[0042] In some embodiments, the areal density of the polymer layer is 0.1g / m 2 -1g / m 2 , for example, 0.1g / m 2 , 0.2g / m 2 , 0.3g / m 2 , 0.4g / m2 0.5 g / m 2 0.6 g / m 2 0.7 g / m 2 0.8 g / m 2 0.9 g / m 2 or 1 g / m 2 .

[0043] In some embodiments, the polymer layer has a liquid absorption amount of 20 wt% to 400 wt% of its own weight, for example 20 wt%, 40 wt%, 60 wt%, 80 wt%, 100 wt%, 150 wt%, 200 wt%, 300 wt%, 350 wt% or 400 wt%. Within the suitable range of liquid absorption amount, the polymer layer has suitable adhesion and liquid retention at the same time.

[0044] In some embodiments, the polymer layer has a liquid absorption amount of 40 wt% to 250 wt% of its own weight.

[0045] In some embodiments, the polymer has a weight average molecular weight of 1.5 x 10 5 - 6 x 10 5 , for example 1.5 x 10 5 , 2 x 10 5 , 2.5 x 10 5 , 3 x 10 5 , 3.5 x 10 5 , 4 x 10 5 , 4.5 x 10 5 , 5 x 10 5 , 5.5 x 10 5 or 6 x 10 5 .

[0046] In some embodiments, the polymer has a softening point of 45 °C to 85 °C, for example 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C or 85 °C.

[0047] The weight average molecular weight of the polymer can be determined by gel chromatography and light scattering method, and the softening point can be determined by Vicat softening point test method.

[0048] In some embodiments, the value S of the ratio of the coverage area of the single-sided polymer layer to the area of the single-sided separator is 5-30, for example 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, or 30. The coverage area of the single-sided polymer layer refers to the area of the coverage region of the single-sided polymer layer. If the coverage region is too small, the liquid absorption capacity of the separator is insufficient, the adhesion sites of the polymer layer to the positive and negative electrode sheets are insufficient, the adhesion of the separator to the positive and negative electrode sheets is poor, the lithium ion transmission distance is large, and the rate performance of the battery is affected. If the coverage region is too large, the lithium ion transmission power is limited, and the rate performance of the battery is also affected.

[0049] In some embodiments, S is 16-28.

[0050] The coverage mode of the polymer layer can not be particularly limited, for example, it can be distributed in a dot matrix manner, etc.

[0051] In some embodiments, the coverage mode of the polymer layer is distributed in a dot matrix manner. The dot matrix can be uniformly distributed circular or quasi-circular regions, that is, the shape of the dots in the dot matrix is circular and / or quasi-circular (such as elliptical or polygonal or irregular circular, etc.).

[0052] In some embodiments, the diameter of each dot in the dot matrix is 5 μm-500 μm, for example 5 μm, 10 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, or 50 μm. The diameter of the dot is measured as an average diameter.

[0053] The polymer layer can be obtained by polymerizing the monomer described above under the action of an initiator and coating the polymer on the base film (or the functional layer on the base film).

[0054] The initiator can be an oil-soluble radical initiator used in the art, and can be at least one of an azo initiator and / or an organic peroxide initiator. The azo initiator can be at least one of azobisisobutyronitrile, azobisisoamyl nitrile, azobisisoheptyl nitrile, and dimethyl azobis-2-methylpropionate; the organic peroxide initiator can be at least one of dibenzoyl peroxide, dicumyl peroxide, di(2,4-dichlorobenzoyl) peroxide, dilauryl peroxide, t-butyl peroxynonane, t-butyl peroxynonadecane, di-sec-butyl peroxydicarbonate, di(hexadecyl) peroxydicarbonate, t-amyl peroxyneodecanoate, t-butyl peroxypivalate, di-(4-t-butylcyclohexyl) peroxydicarbonate, dicyclohexyl peroxydicarbonate, diisopropyl peroxydicarbonate, dibutyl peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, t-butyl peroxy-2-ethylhexanoate, ditetradecyl peroxydicarbonate, t-butyl peroxyacetate, t-amyl peroxybenzoate, di-t-butyl peroxide, cyclohexyl sulfonyl acetyl peroxide, dibenzoyl peroxide, diisobutyryl peroxide, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, di-3-methoxybutyl peroxydicarbonate, and 1,1,3,3-tetramethylbutyl peroxypivalate.

[0055] In some embodiments, the initiator is used in an amount of 0.02 wt% to 5 wt% of the total weight of the monomers.

[0056] In some embodiments, the solvent for the polymerization reaction can be at least one of N,N-dimethylformamide, water, and an alcohol solvent such as methanol, ethanol, and the like.

[0057] In some embodiments, the conditions for the polymerization reaction include a temperature of 60°C to 95°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or 95°C, and a time of 6h to 24h, for example, 6h, 10h, 14h, 18h, 20h, or 24h.

[0058] In some embodiments, the separator further comprises a functional layer located on one side or both sides of the base film and between the base film and the polymer layer.

[0059] In some embodiments, the functional layer comprises a heat-resistant layer. The heat-resistant layer can be located on the positive electrode side and / or the negative electrode side, and can be at least on the positive electrode side.

[0060] In some embodiments, the heat-resistant layer comprises an inorganic material, including but not limited to at least one of Al2O3, boehmite, SiO2, MgO, and TiO2.

[0061] In some embodiments, the heat-resistant layer can further comprise a binder such as sodium carboxymethyl cellulose, lithium polyacrylate, and the like.

[0062] In some embodiments, the content of inorganic material in the heat-resistant layer is 85wt% to 98wt% (for example, 85wt%, 90wt%, 95wt% or 98wt%), and the content of binder is 2wt% to 15wt% (for example, 2wt%, 5wt%, 10wt% or 15wt%).

[0063] The diaphragm can further comprise other functional layers, such as a safety layer, etc., which can be selected according to actual needs and will not be described here.

[0064] In the present application, the first additive has a structure shown in Formula I:

[0065]

[0066] wherein R1, R2and R3are each independently H, methyl or halogen (such as F, Cl, Br, I, etc.); R4is absent or R4is substituted or unsubstituted C1-C6alkyl or substituted or unsubstituted C1-C6alkoxy (O atom can be connected to Si); R5, R6and R7are each independently selected from substituted or unsubstituted C1-C6alkyl, substituted or unsubstituted C1-C6alkoxy (O atom can be connected to Si), substituted or unsubstituted amine group or substituted or unsubstituted amide group, and the substituent group is each independently C1-C2alkyl (such as methyl, ethyl, etc.), C1-C2haloalkyl (such as fluoromethyl, fluoroethyl, etc.) or halogen. Lower steric hindrance of R1, R2and R3is conducive to the reaction of the double bond, and the double bond structure is conducive to the film formation of the additive in the negative electrode, so that the SEI contains polysilane or polysiloxane structure, thereby improving the thermal stability of the SEI.

[0067] In some embodiments, at most one of R1, R2and R3is methyl.

[0068] In some embodiments, R4is absent or R4is substituted or unsubstituted C1-C4alkyl or substituted or unsubstituted C1-C4alkoxy, such as R4is absent or R4is methylene (-CH2-), -CH2CH2-, -CH2CH2CH2-, -CH2O-, -CH2CH2O-, difluoromethylene, -CF2O-, -CH2CF2O-, etc.

[0069] In some embodiments, in the first additive, R4is absent or R4is substituted or unsubstituted C1-C2alkyl (such as methylene or -CH2CH2-) or substituted or unsubstituted C1-C2alkoxy (such as -CH2O- or CH2CH2O-).

[0070] In some embodiments, R5, R6, and R7 are each independently selected from substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy, substituted or unsubstituted amine group, or substituted or unsubstituted amide group.

[0071] In some embodiments, the first additive comprises, but is not limited to, at least one of the compounds having the following structure:

[0072]

[0073] In some embodiments, the content of the first additive in the electrolyte is A1wt% of 0.1wt%-3wt% (i.e., A1 is 0.1-3), for example, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, or 3wt%. Since the reduction product formed by the first additive has better thermal stability than the alkyl lithium carbonate formed by the reduction of conventional carbonates such as ethylene carbonate (EC) and the like at the negative electrode, the thermal stability of the SEI will increase as A1 increases. However, when the amount of the first additive is too much, a too thick SEI layer will be formed on the surface of the negative electrode, which is not conducive to the rapid migration of lithium ions, resulting in poor reaction kinetics of the negative electrode, thereby increasing the risk of lithium plating and diving of the battery.

[0074] In some embodiments, the electrolyte further comprises a second additive, and the second additive is a fluorinated solvent. The fluorinated solvent is conducive to film formation at the negative electrode, and the SEI formed on the surface of the negative electrode is rich in inorganic components such as LiF, which has better thermodynamic properties.

[0075] In some embodiments, the second additive is selected from at least one of fluorinated ethylene carbonate (FEC), fluorinated propylene carbonate, fluorinated ethyl acetate, fluorinated propyl acetate, fluorinated dimethyl carbonate, and fluorinated diethyl carbonate.

[0076] In some embodiments, the content of the second additive in the electrolyte is 5wt%-15wt%, for example, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 15wt%.

[0077] In some embodiments, the electrolyte further comprises a third additive, and the third additive is a sulfur-containing compound. The sulfur-containing compound can form a film on the positive and negative electrodes, improve the thermal stability of the SEI of the positive and negative electrodes, and improve the high-temperature performance of the battery.

[0078] In some embodiments, the content of the third additive in the electrolyte is 0.5wt%-5wt%, for example, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, or 5wt%.

[0079] In some embodiments, the third additive is selected from at least one of 1,3-propane sultone (PS), 1,3-propene sultone (PST), ethylene sulfate (DTD), bis-ethylene sulfate (BiDTD), methane dimesylate (MMDS), trimethylsilylmethane sulfonate, dimethylmethylene sulfonate, 4-acetylphenyl trifluoromethyl sulfonate, phenyl trifluoromethane sulfonate, 6-quinolinyl trifluoromethane sulfonate, and N-ethyl-5-phenylisoxazole-3'-sulfonate.

[0080] In some embodiments, the content of the first additive in the electrolyte is 0.1wt%-3wt%, for example, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt% or 3wt%, the content of the second additive is 5wt%-15wt%, for example, 5wt%, 7wt%, 9wt%, 11wt%, 13wt%

[0081] or 15wt%, and the content of the third additive is 0.5wt%-5wt%, for example, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%. The synergistic effect of the three additives makes the SEI film formed have suitable organic and inorganic composite components, such as lithium silicate, lithium sulfate, lithium sulfite, lithium fluoride, alkyl lithium silicate, alkyl lithium sulfonate, silane polymer, etc., effectively improving the thermal stability of the SEI. In addition, the mixed organic and inorganic lithium salt components formed by the second additive and the third additive are beneficial to assisting the transmission of lithium ions in the SEI film, while the silicon-based polymer formed by the first additive is not conducive to the transmission of lithium ions, but its flexible network structure can better maintain the structural integrity of the SEI. Therefore, the joint application of the three additives can not only increase the thermal stability of the SEI, but also make the SEI formed have good mechanical stability and lithium ion transmission.

[0082] The additive can be obtained by commercial purchase or prepared by methods known in the art.

[0083] In some embodiments, the electrolyte further comprises an alkali metal salt electrolyte.

[0084] In some embodiments, the alkali metal salt electrolyte is a lithium salt.

[0085] In some embodiments, the lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium trifluoromethylsulfonate (LiCF3SO3), lithium difluorophosphate (LiPO2F2), lithium tetrafluoroborate (LiBF4), lithium difluoro(oxalato)borate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0086] In some embodiments, the content of the lithium salt in the electrolyte is 10wt%-20wt%, for example, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%.

[0087] In some embodiments, the electrolyte further includes an aprotic organic solvent.

[0088] In some embodiments, the aprotic organic solvent includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), butylene carbonate (BC), ethyl acetate (EA), ethyl propionate (EP), n-propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), sulfolane (SL), dimethyl sulfone (MSM), dioxolane (DOL), and dimethoxyethane (DME).

[0089] In some embodiments, the content of the aprotic organic solvent in the electrolyte is 50wt%-80wt%, for example, 50wt%, 60wt%, 70wt%, or 80wt%.

[0090] The base film can be a microporous film that is conventional in the art, and in some embodiments, the base film is made of at least one of polyethylene (PE) and polypropylene (PP).

[0091] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector.

[0092] In some embodiments, the positive electrode active material layer includes a positive electrode active material, a first conductive agent, and a first binder.

[0093] In some embodiments, the positive active material is selected from at least one of doped or undoped and coated or uncoated lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, and lithium-rich lithium manganate-based materials. The doping elements can include, but are not limited to, Al, Ti, Mg, W, V, Sb, Bi, Mn, Nb, La, etc. The coating material can be carbon material, metal oxide, etc., such as soft carbon, hard carbon, AI2O3, TiO2, ZrO2, MgO, WO3, etc.

[0094] In some embodiments, the positive active material layer comprises 90wt%-98wt% (e.g., 90wt%, 95wt%, or 98wt%) of the positive active material, 0.5wt%-5wt% (e.g., 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, or 5wt%) of the first conductive agent, and 0.5wt%-5wt% (e.g., 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, or 5wt%) of the first binder.

[0095] In some embodiments, the negative electrode sheet comprises a negative current collector and a negative active material layer on the negative current collector.

[0096] In some embodiments, the negative active material layer comprises a negative active material, a second conductive agent, and a second binder.

[0097] In some embodiments, the negative active material is selected from at least one of carbon-based materials (including but not limited to natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, etc.), silicon-based materials (including but not limited to nano-silicon, amorphous silicon, silicon monoxide, silicon nanowires, silicon-carbon composite materials, etc.), and doped or undoped lithium titanate. The doping elements can be selected from at least one of Al, Ti, Mg, W, V, Sb, Bi, Mn, Nb, La, etc.

[0098] In some embodiments, the negative active material layer comprises 90wt%-98wt% (e.g., 90wt%, 95wt%, or 98wt%) of the negative active material, 0.5wt%-5wt% (e.g., 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, or 5wt%) of the second conductive agent, and 0.5wt%-5wt% (e.g., 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, or 5wt%) of the second binder.

[0099] In some embodiments, the conductive agent includes, but is not limited to, at least one of conductive carbon black, carbon nanotubes, carbon fibers, and Ketjen black. The first conductive agent and the second conductive agent can be the same or different.

[0100] In some embodiments, the binder includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), styrene butadiene rubber emulsion, polytetrafluoroethylene emulsion, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxylated chitosan. The first binder and the second binder can be the same or different.

[0101] The battery in the present application can be a lithium ion battery, and other components of the lithium ion battery and the preparation method thereof can be a conventional selection in the art, without particular limitation.

[0102] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0103] The materials, reagents and the like used in the following examples can be obtained from commercial channels unless otherwise specified.

[0104] The present application will be described in detail below in combination with specific examples, which are used for understanding rather than limiting the present application.

[0105] Example 1

[0106] (1) Preparation of polymer

[0107] 200 parts by weight of water and 300 parts by weight of ethanol were added to a reaction kettle and stirred and dissolved. After complete dissolution, 50 parts by weight of methyl methacrylate, 20 parts by weight of acrylonitrile, and 5 parts by weight of styrene were added and stirred uniformly. After nitrogen was passed for 30 min, the temperature was gradually increased to 75°C, and 2 parts by weight of azobisisobutyronitrile ethanol solution (2 wt% of the total weight of monomers) was added to initiate the reaction. After 12 hours of polymerization initiation, a polymer dispersion was obtained. Water was added to the polymer dispersion, and steam stripping was performed to obtain a polymer water dispersion. The liquid absorption amount of the polymer prepared under this condition was about 150 wt% of the weight, the weight average molecular weight was about 3 x 10 5 , and the softening point was about 60°C.

[0108] (2) Preparation of separator

[0109] A 2-μm-thick barium sulfate layer (composition: 90 wt% barium sulfate, 4.5 wt% lithium polyacrylate, and 4.5 wt% sodium carboxymethyl cellulose) was coated on the surface of a 5-μm-thick polyethylene substrate on the positive electrode side, and then a polymer layer with an area density of 0.2 g / m 2 was coated on both sides of the polyethylene substrate coated with the barium sulfate, and after drying, the required separator was obtained.

[0110] wherein the schematic view is as shown in Figure 1 and Figure 2 The polymer layer is coated in a dot-matrix manner, each dot in the dot-matrix is circular and has a diameter of about 100 μm, and the coverage area of the single-side polymer layer accounts for 20% of the area of the single-side separator, i.e. S is 20.

[0111] (3) Preparation of electrolyte

[0112] In an argon-filled glove box with water and oxygen content less than 0.1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), ethyl propionate (EP) were mixed uniformly in a mass ratio of 1:1:1:1:1, followed by adding 12.5% of the total mass of the electrolyte lithium hexafluorophosphate (LiPF6), and adding 8 wt% of fluoroethylene carbonate (FEC), 3.0 wt% of PS and 1.0 wt% of dimethoxymethylvinylsilane, and mixing uniformly.

[0113] (4) Preparation of battery

[0114] The negative electrode sheet, the separator and the positive electrode sheet were stacked in a certain manner, so that the separator completely separated the positive and negative electrodes, and a roll core was prepared by winding, followed by wrapping with an aluminum plastic film and injecting the above electrolyte, and after packaging, formation, a soft-pack lithium ion battery was obtained.

[0115] Example 2 and Comparative Example 1

[0116] The method described in Example 1 was followed, except that when preparing the polymer, the types of monomers and the feeding weight ratio were different, as shown in Table 1.

[0117] Table 1

[0118] Number First monomer Second monomer Third monomer Weight ratio Liquid uptake Example 1 Methyl methacrylate Acrylonitrile Styrene 10:4:1 150 wt% Example 2a * * * 10:3:2 100 wt% Example 2b * * * 8:0.7:1.3 80 wt% Example 2c * * * 8:1.3:0.7 120 wt% Example 2d * * * 6:3:1 140 wt% Example 2e Methyl acrylate * * * 130 wt% Example 2f * 2-methyl-3-butenenitrile * * 60 wt% Example 2g * * / 10：4 200 wt% Example 2h * * Acrylic acid * 220 wt% Example 2i * * Acrylamide * 220 wt% Example 2j * * Maleic anhydride * 250 wt% Comparative Example 1 * / * 10：1 50 wt%

[0119] Note: In the present application, "*" indicates the same as Example 1, and " / " indicates no addition.

[0120] Example 3 and Comparative Example 2

[0121] The method described in Example 1 was followed, except that the content of the first additive in the electrolyte A1 wt% and the coverage area of the single-side polymer layer accounted for the area of the single-side separator S% were different (the contents of the second additive and the third additive were unchanged), as shown in Table 2, wherein K value represents

[0122]

[0123] Table 2

[0124] Number First additive A1 S K value Example 1 Dimethoxymethylvinylsilane 1.0 20 82.6 Example 3a * 0.1 10 82.0 Example 3b * 0.5 15 83.4 Example 3c * 2.0 20 88.5 Example 3d * 3.0 25 87.2 Example 3e * 0.5 20 78.5 Example 3f * 0.5 30 68.7 Comparative Example 2a * 5 20 100.2 Comparative Example 2b * 3 5 110.5 Comparative Example 2c * 0.5 40 58.8 Comparative Example 2d / 0 20 68.4

[0125] Comparative Example 3a

[0126] The procedure described in Example 1 was followed, except that the separator used was only coated with the boron stone coating, and not with the polymer layer.

[0127] Comparative Example 3b

[0128] The procedure described in Example 1 was followed, except that the polymer was applied as a full coverage coating.

[0129] Example 4 and Comparative Example 4

[0130] The procedure described in Example 1 was followed, except that the type of the first additive of the electrolyte was different, as shown in Table 3.

[0131] Table 3

[0132] Number First additive Example 1 Dimethoxymethylvinylsilane (Formula VI) Example 4a Diethylmethylvinylsilane (Formula II) Example 4b Allyltrimethylsilane (Formula III) Example 4c Allyloxytrimethylsilane (Formula IV) Example 4d Vinyl dimethyl ethoxysilane (Formula V) Example 4e Vinyltrimethoxysilane (Formula VII) Comparative Example 4 Tetraethylsilane

[0133] Example 5 and Comparative Example 5, Comparative Example 6

[0134] The procedure described in Example 1 was followed, except that the type and content of the second additive and the third additive of the electrolyte were different, as shown in Table 4.

[0135] Table 4

[0136]

[0137]

[0138] Test Example

[0139] (1) Rate and cycle performance test

[0140] The voltage window of the test of the lithium ion battery was set to 3.0-4.45V. The lithium ion battery was charged to full by constant current charging to the upper limit voltage and then constant voltage, and then discharged at currents of 0.1C, 0.2C, 0.5C, 1C and 2C, respectively, to test the rate discharge performance of the prepared lithium ion battery.

[0141] The discharge current of the cycle test was 0.7C, and the capacity retention rate was calculated based on the initial capacity of the discharge capacity at 0.1C.

[0142] Both the cycle and rate tests were carried out in a constant temperature oven at 25°C.

[0143] (2) Hot box passing test

[0144] The lithium ion battery was charged to full by constant current and constant voltage of 0.5C, and the full battery was placed in a constant temperature oven at 20±5℃, then, the temperature was raised to the target temperature at a rate of 5℃ / min, and kept constant for 30min. Within 30min, the battery did not catch fire, did not explode, indicating that the battery passed the hot box test.

[0145] The electrochemical performance and hot box passing rate performance of the batteries of each example and comparative example are shown in Table 5.

[0146] Table 5

[0147]

[0148]

[0149]

[0150] From Example 1 and Examples 2a-2j, it can be seen that by properly regulating the composition of the polymer layer, the battery can obtain better rate and cycle performance, and at the same time have good hot box passing rate. From Comparative Example 1, it can be seen that due to the absence of cyano groups in the polymer layer, metal ions of the positive electrode are more likely to migrate to the negative electrode during heating, catalyzing the decomposition of SEI and electrolyte, so the cycle and hot box passing rate performance of the battery are significantly negatively affected.

[0151] From Example 1 and Examples 3a-3f, it can be seen that by properly regulating the values of A1 and S, the prepared battery also has good comprehensive performance. From Comparative Example 2a, it can be seen that when the amount of the first additive of the electrolyte is too much, it will polymerize and accumulate too much on the surface of the negative electrode, resulting in a too thick SEI, thus the rate and cycle performance are significantly deteriorated. From Comparative Example 2b, it can be seen that when the amount of the first additive of the electrolyte is 3wt% and the proportion of the coverage area of the single-sided polymer layer to the area of the single-sided separator is 5%, the K value is 110.5, at this time, due to the relatively thick SEI and the relatively low proportion of the interaction between the separator and the electrolyte, the rate performance and cycle performance of the battery are both relatively poor, and the hot box passing rate is also deteriorated. From Comparative Example 2c, it can be seen that when the proportion of the coverage area of the single-sided polymer layer to the area of the single-sided separator is 40%, although the hot box passing rate is good, at this time, the lithium ion migration in the electrolyte may be slow, and the rate performance and cycle stability are both deteriorated. From Comparative Example 2d, it can be seen that when no first additive is added to the electrolyte, due to the instability of the formed SEI, the cycle performance and hot box passing rate of the battery are also deteriorated.

[0152] From Example 1 and Comparative Example 3a, it is known that the uncoated polymer layer, due to the poor liquid retention of the electrolyte by the separator and the poor contact of the separator with the positive and negative electrodes, the performance is significantly deteriorated. From Comparative Example 3b, it is known that when the coating rate of the polymer is 100%, the migration of lithium ions is slow, thus the rate performance is inhibited, and the capacity retention of the cycle is also deteriorated.

[0153] From Example 1 and Examples 4a-4e, it is known that the change of the type of the first additive does not significantly change the performance. From Comparative Example 4, it is known that when the first additive is replaced by tetraethylsilane, due to the fact that the added tetraethylsilane does not have a double bond, it cannot form a film on the surface of the negative electrode, and the comprehensive performance of the battery is deteriorated.

[0154] From Example 1 and Examples 5a-5f, it is known that by properly adjusting the second and third additives, the obtained battery also has good comprehensive performance. From Comparative Examples 5 and 6, it is known that when the second additive and the third additive are not added to the electrolyte, due to the influence on the stability and impedance of the SEI film, the cycle performance and rate performance of the battery are significantly deteriorated.

[0155] It should be noted that in this document, the terms "comprise", "comprising", or any other variant thereof are intended to cover non-exclusive inclusions, so that processes, methods, articles, or devices that include a series of elements not only include those elements, but also include other elements not explicitly listed, or inherent to such processes, methods, articles, or devices. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or device that includes the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to the order of performing the functions shown or discussed, but can also include performing the functions in a substantially simultaneous manner or in reverse order, for example, the described method can be performed in an order different from that described, and various steps can be added, omitted, or combined. In addition, the features described with reference to certain examples can be combined in other examples.

[0156] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A battery, characterized in that: The battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the separator comprises a base film and polymer layers located on both sides of the base film; The monomers of the polymer layer include a first monomer and a second monomer, the first monomer is selected from an acrylate monomer, and the second monomer is an olefin nitrile monomer; The electrolyte includes a first additive having a structure shown in Formula I: Formula I, wherein R1, R2 and R3 are each independently H, methyl or halogen; R4 is absent or R4 is a substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C1-C6 alkoxy group; R5, R6 and R7 are each independently selected from a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C1-C6 alkoxy group, a substituted or unsubstituted amino group or a substituted or unsubstituted amide group, and the substituents are each independently C1-C2 alkyl group, C1-C2 haloalkyl group or halogen; The battery satisfies the relationship: ; Among them, A1 is the content of the first additive in the electrolyte, the unit is wt%, A1 is 0.1-3; S is the ratio of the coverage area of ​​the single-sided polymer layer to the area of ​​the single-sided diaphragm, the unit is %, and S is 5-30.

2. The battery according to claim 1, characterized in that The first monomer is selected from at least one of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate and trifluorobutyl methacrylate.

3. The battery according to claim 1, characterized in that The second monomer is at least one selected from acrylonitrile, crotononitrile, 2-methyl-3-butenenitrile and methacrylonitrile.

4. The battery according to claim 1, characterized in that The monomers of the polymer layer further include a third monomer, and the third monomer is selected from at least one of acrylic monomers, acrylamide monomers, styrene monomers and anhydride monomers.

5. The battery according to claim 1, characterized in that Among the monomers of the polymer layer, the first monomer accounts for 40 wt% to 100 wt%, the second monomer accounts for 5 wt% to 40 wt%, and the third monomer accounts for 0 wt% to 20 wt%; The liquid absorption capacity of the polymer layer is 20wt%-400wt% of its own weight; The weight average molecular weight of the polymer is 1.5×10 5 -6×10 5 ; The softening point of the polymer is 45°C-85°C.

6. The battery according to claim 1, characterized in that S is 16-28.

7. The battery according to claim 1, characterized in that The polymer layer is covered in a lattice-like distribution, wherein the shape of the points in the lattice-like distribution is circular and / or quasi-circular; The diameter of each dot in the dot matrix distribution is 5 μm to 500 μm.

8. The battery according to claim 1, characterized in that In the first additive, R4 is absent or R4 is a substituted or unsubstituted C1-C4 alkyl group or a substituted or unsubstituted C1-C4 alkoxy group; In the first additive, R5, R6 and R7 are each independently selected from a substituted or unsubstituted C1-C2 alkyl group, a substituted or unsubstituted C1-C2 alkoxy group, a substituted or unsubstituted amine group or a substituted or unsubstituted amide group.

9. The battery according to claim 1 or 8, characterized in that The first additive comprises at least one compound having the following structure: 。 10. The battery according to claim 1, characterized in that The electrolyte further comprises a second additive and a third additive, the second additive being a fluorinated solvent and the third additive being a sulfur-containing compound; The second additive is selected from at least one of fluoroethylene carbonate, fluoropropylene carbonate, fluoroethyl acetate, fluoropropyl acetate, fluorodimethyl carbonate and fluorodiethyl carbonate; The third additive is selected from at least one of 1,3-propane sultone (PS), 1,3-propylene sultone (PST), vinyl sulfate (DTD), bis(vinyl sulfate) (BiDTD), methylene disulfonate (MMDS), trimethylsilylmethanesulfonate, dimethylmethylenesulfonate, 4-acetylphenyl trifluoromethanesulfonate, phenyl trifluoromethanesulfonate, 6-quinolyl trifluoromethanesulfonate, and N-ethyl-5-phenylisoxazole-3'-sulfonate; In the electrolyte, the content of the second additive is 5wt%-15wt%, and the content of the third additive is 0.5wt%-5wt%.

11. The battery according to claim 1, characterized in that The electrolyte further comprises an alkali metal salt electrolyte and an aprotic organic solvent; The alkali metal salt electrolyte is a lithium salt; the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium trifluoromethylsulfonate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate and lithium dioxalatoborate; The aprotic organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butylene carbonate, ethyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate, sulfolane, dimethyl sulfone, dioxolane and ethylene glycol dimethyl ether; The content of lithium salt in the electrolyte is 10 wt %-20 wt %, and the content of aprotic organic solvent is 50 wt %-80 wt %.

12. The battery according to claim 1, characterized in that The diaphragm also includes a functional layer located on one side or both sides of the base film and between the base film and the polymer layer; the functional layer includes a heat-resistant layer; the heat-resistant layer includes at least one of Al2O3, boehmite, SiO2, MgO and TiO2; the material of the base film includes at least one of polyethylene (PE) and polypropylene (PP).

13. The battery according to claim 1, characterized in that The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector; The positive electrode active material layer comprises a positive electrode active material, a first conductive agent and a first binder; the positive electrode active material is selected from at least one of the following materials, which may be doped or undoped and coated or uncoated: lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate and lithium-rich lithium manganese oxide-based materials; The positive electrode active material layer includes 90 wt % to 98 wt % of a positive electrode active material, 0.5 wt % to 5 wt % of a first conductive agent, and 0.5 wt % to 5 wt % of a first binder.

14. The battery according to claim 1, characterized in that The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector; The negative electrode active material layer comprises a negative electrode active material, a second conductive agent and a second binder; The negative electrode active material is selected from at least one of carbon-based materials, silicon-based materials and doped or undoped lithium titanate; The negative electrode active material layer includes 90 wt % to 98 wt % of a negative electrode active material, 0.5 wt % to 5 wt % of a second conductive agent, and 0.5 wt % to 5 wt % of a second binder.

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