Secondary battery, preparation method thereof and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a positive pole piece, a negative pole piece and a diaphragm, a positive pole material layer comprises a first oligomer, a negative pole material layer comprises a second oligomer, and the diaphragm comprises a third oligomer, the first oligomer, the second oligomer and the third oligomer have the same repeating unit, and the thermal decomposition temperatures of the first oligomer, the second oligomer and the third oligomer are respectively and independently between 90 DEG C and 180 DEG C; in a differential scanning calorimetry test spectrogram of the positive electrode material layer, a first thermal decomposition peak exists between 90 DEG C and 180 DEG C, and the temperature of the first thermal decomposition peak is TC; in a differential scanning calorimetry test spectrogram of the negative electrode material layer, a second thermal decomposition peak exists between 90 DEG C and 180 DEG C, and the temperature of the second thermal decomposition peak is TA; in a differential scanning calorimetry test spectrogram of the diaphragm, a third thermal decomposition peak exists between 90 DEG C and 180 DEG C, and the temperature of the third thermal decomposition peak is TS; 0 DEG C < = Max( TC, TA, TS)-Min (TC, TA, TS) < = 20 DEG C, and the interface problem and the cycle performance of the secondary battery in the charge-discharge cycle process can be improved.

Description

Technical Field

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

[0002] The distance between the diaphragm and the electrode is an important factor affecting the dynamics and interface state of secondary batteries. During the cycle of secondary batteries, the diaphragm and the electrode are easily lost due to factors such as the volume expansion of active materials and interfacial side reactions, which in turn leads to an increase in the impedance of the secondary battery and the problem of cycle attenuation of the secondary battery. At present, the conventional improvement method is to provide an adhesive coating on the diaphragm to make the surface of the electrode and the diaphragm bonded, but the bonding effect is limited to the surface of the electrode and does not act on the interior of the electrode material layer. During the charge and discharge process of the secondary battery, especially in high-expansion systems such as Si-containing negative electrodes, the diaphragm is still prone to losing adhesion with the electrode, leading to interface problems and affecting the cycle performance of the secondary battery. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery and its preparation method, as well as an electronic device, to improve the adhesion between the separator and the positive and negative electrode sheets, thereby resolving interface issues and improving the cycle performance of the secondary battery. The specific technical solution is as follows:

[0004] It should be noted that, in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries.

[0005] The first aspect of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate and a separator, wherein the positive electrode plate includes a positive electrode material layer, the negative electrode plate includes a negative electrode material layer; the positive electrode material layer includes a first oligomer, the negative electrode material layer includes a second oligomer, and the separator includes a third oligomer, the first oligomer, the second oligomer and the third oligomer have the same repeating unit and the thermal decomposition temperature is independently between 90°C and 180°C; in the differential scanning calorimetry test spectrum of the positive electrode material layer, there is a first thermal decomposition peak between 90°C and 180°C, and the temperature of the first thermal decomposition peak is T C In the differential scanning calorimetry test spectrum of the negative electrode material layer, there is a second thermal decomposition peak between 90°C and 180°C, and the temperature of the second thermal decomposition peak is T A In the differential scanning calorimetry test spectrum of the diaphragm, there is a third thermal decomposition peak between 90℃ and 180℃, and the temperature of the third thermal decomposition peak is T S ;0℃≤Max(T C ,T A ,T S )-Min(T C ,T A ,TS )≤20°C. In some embodiments of the present application, 8°C≤Max(T C ,T A ,T S )-Min(T C ,T A ,T S )≤17°C. The first oligomer, the second oligomer and the third oligomer have the same repeating unit and the thermal decomposition temperature is independently between 90°C and 180°C. C ,T A ,T S )-Min(T C ,T A ,T S ) within the above range, indicating that the first, second, and third oligomers are the same polymer with the same or similar molecular weight. Thus, in the secondary battery provided herein, the inclusion of the same polymer in the positive electrode material layer and the separator facilitates improved adhesion between the positive electrode plate and the separator, and the inclusion of the same polymer in the negative electrode material layer and the separator facilitates improved adhesion between the negative electrode plate and the separator, thereby improving interfacial issues and cycle performance during the secondary battery's charge and discharge cycles.

[0006] In some embodiments of the present application, the peel force F1 between the negative electrode sheet and the separator is 15 N / m to 50 N / m, and the peel force F2 between the positive electrode sheet and the separator is 11 N / m to 45 N / m. The peel force F1 between the negative electrode sheet and the separator and the peel force F2 between the positive electrode sheet and the separator are within the above ranges, indicating that there is good adhesion between the negative electrode sheet and the separator, and between the positive electrode sheet and the separator. During the charge and discharge process of the secondary battery, the adhesion between the negative electrode sheet and the separator, and between the positive electrode sheet and the separator is not easily lost, which is beneficial to improving the interface problems between the negative electrode sheet and the separator, and between the positive electrode sheet and the separator, as well as the cycle performance of the secondary battery.

[0007] In some embodiments of the present application, the porosity of the diaphragm after being soaked in dimethyl carbonate for 1 minute is P1, and the porosity of the diaphragm after being soaked in dimethyl carbonate for 15 minutes is P2, and 1≤P2 / P1≤1.55. In some embodiments of the present application, 1≤P2 / P1≤1.25. P2 / P1 is within the above range, that is, the porosity of the diaphragm changes before and after being soaked in dimethyl carbonate, indicating that the substances present in the pores of the diaphragm are dissolved during the soaking process. At the same time, the molecular weight of the oligomers generated by in situ polymerization is usually small and can be dissolved in dimethyl carbonate, indicating that the third oligomer generated by in situ polymerization exists in the diaphragm.

[0008] In some embodiments of the present application, the positive electrode, the negative electrode, and the separator include fluorinated organic compounds, and the fluorinated organic compounds include at least one of fluorinated carbonates, fluorinated carboxylates, fluorinated linear ethers, fluorinated cyclic ethers, fluorinated sulfone compounds, fluorinated phosphides, or fluorinated carbamates. The above-mentioned types of fluorinated organic compounds have strong electronegativity, and the fluorine atoms or fluorinated functional groups therein can form van der Waals forces with the molecular weight, which is conducive to increasing the interaction force between the molecular chains and reducing the crystallinity of the molecular chains, so that a network-like connection can be formed between the molecular chains, thereby improving the adhesion between the positive electrode and the separator, and between the negative electrode and the separator, and further improving the interface problems and cycle performance during the cycle.

[0009] In some embodiments of the present application, the negative electrode material layer includes a silicon material; the mass percentage of silicon element is W1 based on the mass of the negative electrode material layer; in a thermogravimetric analysis test of the negative electrode material layer, the weight loss rate of the negative electrode material layer between 90°C and 180°C is m; and 0.01≤100m / W1≤0.11. Controlling 100m / W1 within the above range allows the silicon content in the negative electrode material layer to better match the bonding network within the negative electrode material layer and between the negative electrode material layer and the separator. During the charge and discharge process of the secondary battery, when the negative electrode material undergoes volume changes, the negative electrode plate is less likely to lose adhesion with the separator, thereby improving the interface between the negative electrode plate and the separator and the cycle performance of the secondary battery.

[0010] In some embodiments of the present application, the negative electrode plate includes a negative electrode material layer, wherein the thickness of the negative electrode material layer is H μm; in a thermogravimetric analysis of the negative electrode material layer, the weight loss rate of the negative electrode material layer between 90° C. and 180° C. is m; and 0.6 ≤ m / H×100 ≤ 6.3. Controlling m / H×100 within the above range allows the total silicon content in the negative electrode material layer to better match the bonding network within the negative electrode material layer and between the negative electrode material layer and the separator. During the charge and discharge process of the secondary battery, when the negative electrode material undergoes volume changes, the negative electrode plate is less likely to lose adhesion with the separator, thereby improving the interface between the negative electrode plate and the separator and the cycle performance of the secondary battery.

[0011] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics:

[0012] (1) The positive electrode material layer includes a positive electrode binder. Based on the mass of the positive electrode material layer, the mass percentage of the positive electrode binder is W2, and 0.5%≤W2≤3.0%;

[0013] (2) The negative electrode material layer includes a negative electrode binder. Based on the mass of the negative electrode material layer, the mass percentage of the negative electrode binder is W3, and 2%≤W3≤10%.

[0014] In some embodiments of the present application, the first oligomer, the second oligomer, and the third oligomer each independently include at least one of the following functional groups: -COO-, -O-CO-O-, -SO2O-, -PO4, -COOH, -SO2-, -SO-, -CONH2-, -CN, -O-, or -OBO-. When the first oligomer, the second oligomer, and the third oligomer include these functional groups, this facilitates the dissociation of lithium salts in the electrolyte and improves the ionic conductivity of the electrolyte, thereby improving interfacial issues during the charge and discharge process of the secondary battery and enhancing the cycle performance of the secondary battery while maintaining good kinetic performance.

[0015] A secondary battery that satisfies at least one of the above characteristics is beneficial to improving interface problems during the charge and discharge process of the secondary battery and improving the cycle performance of the secondary battery.

[0016] A second aspect of the present application provides a method for preparing a secondary battery according to any one of the aforementioned embodiments, comprising the following steps:

[0017] (1) obtaining an electrolyte solution, the electrolyte solution comprising a monomer, a solvent, and an electrolyte salt, wherein the mass percentage W4 of the monomer is 2% to 80% based on the mass of the electrolyte solution;

[0018] Wherein, the monomer includes a first monomer and a second monomer, based on the total mass of the monomers, the mass percentage content W41 of the first monomer is 1% to 99%, and the mass percentage content W42 of the second monomer is 1% to 99%; the first monomer includes at least one of an acrylate monomer, a carbonate monomer, a sulfate monomer, a sulfonate monomer, a phosphate monomer, a carboxylate monomer, a sulfone monomer, an amide monomer, a nitrile monomer or an ether monomer; the second monomer includes at least one of an acrylate monomer, an amide monomer or a borate monomer;

[0019] (2) Injecting an electrolyte into a housing provided with an electrode assembly to initiate polymerization of monomers, and obtaining a secondary battery after the polymerization is completed; wherein the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator.

[0020] The preparation method provided in this application triggers in-situ polymerization of the first and second monomers, allowing the generated second and third oligomers to interpenetrate each other, thereby strengthening the interaction between the negative electrode material layer and the separator. Similarly, the first and third oligomers interpenetrate each other, further strengthening the interaction between the positive electrode plate and the separator. By regulating the mass percentage of the monomers in the electrolyte and the mass percentage of the first and second monomers in the monomers within the aforementioned ranges, and selecting the aforementioned types of first and second monomers, in the secondary battery obtained after in-situ polymerization, the positive electrode plate, the negative electrode plate, and the separator can form a single entity, thereby achieving good adhesion between the positive electrode plate and the separator, and between the negative electrode plate and the separator, thereby improving interfacial issues during the secondary battery cycle and enhancing its cycle performance.

[0021] In some embodiments of the present application, the electrolyte further includes a fluorinated organic compound, and the fluorinated organic compound includes at least one of a fluorinated carbonate, a fluorinated carboxylic acid ester, a fluorinated linear ether, a fluorinated cyclic ether, a fluorinated sulfone compound, a fluorinated phosphide or a fluorinated carbamate; based on the mass of the electrolyte, the mass percentage W5 of the fluorinated organic compound is 1% to 30%.

[0022] In some embodiments of the present application, the preparation method satisfies at least one of the following characteristics:

[0023] (1) Fluorinated carbonates include at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, monofluoropropylene carbonate, trifluoropropylene carbonate, 4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]-dioxane-2-one, 4-(2,3,3,3-tetrafluoro-2-trifluoromethylpropyl)-[1,3]dioxane-2-one, 2,2,2-trifluoroethyl methyl carbonate, 2,2-difluoroethyl ethyl carbonate, ethyl (2,2,2-trifluoroethyl) carbonate, ethyl (1-fluoroethyl) carbonate, or 2,2,2-trifluoroethyl (1-fluoroethyl) carbonate;

[0024] The fluorocarboxylic acid ester includes at least one of α-fluoroγ-butyrolactone, β-fluoroγ-butyrolactone, methyl trifluoroacetate, ethyl trifluoroacetate, 2-fluoroethyl acetate, ethyl fluoroacetate, methyl 2,2,2-trifluoroacetate, methyl 2,2-difluoroacetate, ethyl 2,2,2-trifluoroacetate, propyl 2,2,2-trifluoroacetate, butyl 2,2,2-trifluoroacetate or hexyl 2,2,2-trifluoroacetate;

[0025] The fluorinated linear ether includes at least one of fluoro-1,2-diethoxyethane, difluoro-1-ethoxy-2-methoxyethane, trifluoro-1-ethoxy-2-methoxyethane, fluoro-1,2-diethoxyethane, difluoro-1,2-diethoxyethane, trifluoro-1,2-diethoxyethane, tetrafluoro-1,2-diethoxyethane, tetrafluoro-1,2-diethoxyethane, pentafluoro-1,2-diethoxyethane or hexafluoro-1,2-diethoxyethane;

[0026] The fluorinated cyclic ether includes at least one of 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane or 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane;

[0027] The fluorinated sulfone compound includes at least one of 3,3,3-trifluoropropyl methyl sulfone, 3-fluoro-1,3-propane sultone, 2-fluorotetrahydrothiophene-1,1-dioxide, 3-fluorotetrahydrothiophene-1,1-dioxide, trifluoromethyl isopropyl sulfone or trifluoromethyl propyl methyl sulfone;

[0028] The fluorinated phosphide includes at least one of tris(2,2,2-trifluoroethyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane-2-oxide, 2-(2,2,3,3,3-pentafluoropropoxy)-1,3,2-dioxaphospholane, or 2-(2,2,3,3,3-pentafluoropropoxy)-4-(trifluoromethyl)-1,3,2-dioxaphospholane;

[0029] The fluorocarbamate includes at least one of 2,2,2-trifluoroethyl-N,N-dimethylcarbamate, 1,1,1,3,3,3-hexafluoropropyl-N,N-dimethylcarbamate, 2,2,2-trifluoroethyl-N,N-diethylcarbamate, or 1,1,1,3,3,3-hexafluoropropyl-N,N-diethylcarbamate;

[0030] (2) the carbonate monomer includes at least one of vinyl ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate or chloroethylene carbonate;

[0031] The sulfate monomer includes at least one of vinyl sulfite, vinyl sulfite, 4-methyl vinyl sulfate or 4-ethyl vinyl sulfate;

[0032] The sulfonate monomer includes at least one of 1,3-propylene sultone, 1,4-butane sulfonate or methylenedisulfonate;

[0033] The phosphate monomer includes at least one of dimethyl vinyl phosphate, triethyl vinyl phosphate, diethyl propenyl phosphate, triethyl butenyl phosphate, diethyl (I)-buten-2-yl phosphonate, diethyl ethynyl phosphate, vinyl trifluoromethyl phosphate, vinyl-1-trifluoroethyl phosphate, diethyl fluorovinyl phosphate or 1-trifluoropropenylethyl phosphate;

[0034] Carboxylate monomers include vinyl acetate;

[0035] The sulfone monomer includes at least one of methyl vinyl sulfone, ethyl vinyl sulfone, sulfolene, sulfolane or ethylene sulfoxide;

[0036] Amide monomers include acrylamide;

[0037] The nitrile monomer includes at least one of acrylonitrile, succinonitrile, glutaronitrile or adiponitrile;

[0038] The ether monomer includes at least one of 1,3-dioxolane, ethylene oxide, 1,2-propylene oxide, 4-methyl-1,3-dioxolane tetrahydrofuran, 2-methyltetrahydrofuran, 14-dioxane, ethylene glycol dimethyl ether, ethylene glycol diglycidyl ether or triethylene glycol divinyl ether;

[0039] Acrylate monomers include acrylic acid, methacrylic acid, methyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, butyl acrylate, isodecyl acrylate, isooctyl acrylate, lauryl acrylate, isobornyl acrylate, isobornyl methacrylate, ethoxyethoxyethyl acrylate, cyanoacrylate, caprolactone acrylate, 2-phenoxyethyl acrylate, tetrahydrofuran acrylate, ethyl tetrahydrofuran acrylate, cyclotrimethylolpropane acrylate, 2-carboxyethyl acrylate, cyclohexyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, triethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diolefin acrylate, tetraethylene glycol dimethacrylate, 1,4-butanediol at least one of 1,4-butanediol diacrylate, 1,3-butanediol triacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, tripropylene glycol diacrylate, dipropylene glycol dimethacrylate, tripropylene glycol diacrylate, tripropylene glycol dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, 2(propoxylated)neopentyl glycol diacrylate, methoxypolyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, methoxypolyethylene glycol methacrylate, pentaerythritol triacrylate, propoxylated glycerol triacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, di(trimethylolpropane) tetraacrylate, or pentaerythritol tetraacrylate;

[0040] The borate monomer includes at least one of phenyl borate, methyl borate, ethyl borate, benzyl borate or 4-fluorophenyl borate.

[0041] A secondary battery that satisfies at least one of the above characteristics is beneficial to improving interface problems during the charge and discharge process of the secondary battery and improving the cycle performance of the secondary battery.

[0042] In some embodiments of the present application, the preparation method satisfies at least one of the following characteristics:

[0043] (1) 3% ≤ W4 ≤ 50%;

[0044] (2) 2% ≤ W5 ≤ 20%;

[0045] (3) fluorocarbonates including at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, trifluoropropylene carbonate, 2,2,2-trifluoroethyl methyl carbonate, 2,2-difluoroethyl ethyl carbonate, or ethyl (2,2,2-trifluoroethyl) carbonate;

[0046] The fluorocarboxylate includes at least one of α-fluoroγ-butyrolactone, methyl trifluoroacetate, ethyl trifluoroacetate, ethyl 2-fluoroacetate, methyl 2,2,2-trifluoroacetate, or methyl 2,2-difluoroacetate;

[0047] The fluorinated linear ether includes at least one of fluorinated 1,2-diethoxyethane, difluoro 1-ethoxy-2-methoxyethane, trifluoro 1-ethoxy-2-methoxyethane, or tetrafluoro 1,2-diethoxyethane;

[0048] The fluorinated cyclic ether includes at least one of 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane or 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane;

[0049] The fluorinated sulfone compound includes at least one of 3,3,3-trifluoropropyl methyl sulfone or trifluoromethyl isopropyl sulfone;

[0050] The fluorinated phosphide includes at least one of tris(2,2,2-trifluoroethyl)phosphate or tris(2,2,2-trifluoroethyl)phosphate;

[0051] The fluorocarbamate includes at least one of 2,2,2-trifluoroethyl-N,N-dimethylcarbamate, 1,1,1,3,3,3-hexafluoropropyl-N,N-dimethylcarbamate, or 2,2,2-trifluoroethyl-N,N-diethylcarbamate;

[0052] (4) The carbonate monomer includes at least one of vinyl ethylene carbonate and propylene carbonate;

[0053] The sulfate monomer includes at least one of vinyl sulfite or vinyl sulfite;

[0054] The sulfonate monomer includes at least one of 1,3-propylene sultone or 1,4-butane sulfonate;

[0055] The phosphate monomer includes at least one of dimethyl vinyl phosphate, triethyl vinyl phosphate, diethyl propylene phosphate, vinyl-1-trifluoroethyl phosphate or diethyl fluorovinyl phosphate;

[0056] Carboxylate monomers include vinyl acetate;

[0057] The sulfone monomer includes at least one of methyl vinyl sulfone, cyclopentane sulfone or cyclohexane sulfoxide;

[0058] Amide monomers include acrylamide;

[0059] The nitrile monomer includes at least one of acrylonitrile, succinonitrile, glutaronitrile or adiponitrile;

[0060] The ether monomer includes at least one of 1,3-dioxolane, ethylene oxide or 1,2-propylene oxide;

[0061] The acrylic acid ester monomer includes at least one of methyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1-4-butanediol dimethacrylate, 1,3-butanediol triacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, propoxylated glycerol triacrylate, di(trimethylolpropane) tetraacrylate or pentaerythritol tetraacrylate;

[0062] The borate ester monomer includes at least one of methyl borate or ethyl borate.

[0063] A secondary battery that satisfies at least one of the above characteristics is beneficial to improving interface problems during the charge and discharge process of the secondary battery and improving the cycle performance of the secondary battery.

[0064] A third aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments or the secondary battery manufactured by the manufacturing method in any of the aforementioned embodiments.

[0065] Beneficial effects of this application:

[0066] The present application provides a secondary battery and an electronic device, wherein the secondary battery includes a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet includes a positive electrode material layer, and the negative electrode sheet includes a negative electrode material layer; the positive electrode material layer includes a first oligomer, the negative electrode material layer includes a second oligomer, and the separator includes a third oligomer, wherein the first oligomer, the second oligomer, and the third oligomer have the same repeating unit and the thermal decomposition temperature is independently between 90° C. and 180° C.; in a differential scanning calorimetry test spectrum of the positive electrode material layer, a first thermal decomposition peak exists between 90° C. and 180° C., and the temperature of the first thermal decomposition peak is T C In the differential scanning calorimetry test spectrum of the negative electrode material layer, there is a second thermal decomposition peak between 90°C and 180°C, and the temperature of the second thermal decomposition peak is T A In the differential scanning calorimetry test spectrum of the diaphragm, there is a third thermal decomposition peak between 90℃ and 180℃, and the temperature of the third thermal decomposition peak is T S ;0℃≤Max(T C ,T A ,T S)-Min(T C ,T A ,T S )≤20℃. When Max(T C ,T A ,T S )-Min(T C ,T A ,T S ) within the above range, indicating that the first, second, and third oligomers are the same polymer with the same or similar molecular weight. Thus, in the secondary battery provided herein, the inclusion of the same polymer in the positive electrode material layer and the separator facilitates improved adhesion between the positive electrode plate and the separator, and the inclusion of the same polymer in the negative electrode material layer and the separator facilitates improved adhesion between the negative electrode plate and the separator, thereby improving interfacial issues and cycle performance during the secondary battery's charge and discharge cycles.

[0067] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0069] Figure 1 This is a differential scanning calorimetry test spectrum of the positive electrode material layer in Example 1;

[0070] Figure 2 This is a differential scanning calorimetry test spectrum of the negative electrode material layer in Example 1;

[0071] Figure 3 This is a differential scanning calorimetry test spectrum of the diaphragm in Example 1;

[0072] Figure 4 GC-MSD comparison spectrum of the positive electrode material layer, negative electrode material layer and separator in Example 1. DETAILED DESCRIPTION

[0073] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0074] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0075] The first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive electrode material layer, the negative electrode sheet comprises a negative electrode material layer; the positive electrode material layer comprises a first oligomer, the negative electrode material layer comprises a second oligomer, and the separator comprises a third oligomer, wherein the first oligomer, the second oligomer, and the third oligomer have the same repeating unit and each independently has a thermal decomposition temperature between 90°C and 180°C. In a differential scanning calorimetry (DSC) spectrum of the positive electrode material layer, a first thermal decomposition peak exists between 90°C and 180°C, and the temperature of the first thermal decomposition peak is T C In the differential scanning calorimetry test spectrum of the negative electrode material layer, there is a second thermal decomposition peak between 90°C and 180°C, and the temperature of the second thermal decomposition peak is T A In the differential scanning calorimetry test spectrum of the diaphragm, there is a third thermal decomposition peak between 90℃ and 180℃, and the temperature of the third thermal decomposition peak is T S ;0℃≤Max(T C ,T A ,T S )-Min(T C ,T A ,T S )≤20°C. In some embodiments of the present application, 8°C≤Max(T C ,T A ,T S )-Min(T C ,T A ,T S )≤17℃. For example, Max(T C ,T A ,T S )-Min(T C ,T A ,T S ) can be 0℃, 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, 9℃, 10℃, 11℃, 12℃, 13℃, 14℃, 15℃, 16℃, 17℃, 18℃, 19℃, 20℃ or a range consisting of any two values therebetween.

[0076] The temperature T of the first thermal decomposition peak in the DSC test of the positive electrode material layer C Corresponding to the thermal decomposition temperature of the first oligomer, the temperature T of the second thermal decomposition peak in the DSC test of the negative electrode material layer is A Corresponding to the thermal decomposition temperature of the second oligomer, the temperature T of the third thermal decomposition peak in the DSC test of the membrane SCorresponding to the thermal decomposition temperature of the third oligomer. C ,T A ,T S )-Min(T C ,T A ,T S ) is within the above range, that is, the positive electrode material layer, the negative electrode material layer and the separator have the same or similar thermal decomposition peaks between 90°C and 180°C. At the same time, the first oligomer, the second oligomer and the third oligomer have the same repeating unit and the thermal decomposition temperature is independently between 90°C and 180°C. When Max(T C ,T A ,T S )-Min(T C ,T A ,T S ) is within the above range, indicating that the first oligomer, the second oligomer, and the third oligomer are the same polymer with the same or similar molecular weight. Therefore, in the secondary battery provided by the present application, the positive electrode material layer and the separator contain the same polymer, which is beneficial to improving the adhesion between the positive electrode plate and the separator, and the negative electrode material layer and the separator contain the same polymer, which is beneficial to improving the adhesion between the negative electrode plate and the separator, thereby improving the interface problem and cycle performance of the secondary battery during the charge and discharge cycle. In the present application, Max(T C ,T A ,T S ) refers to T C 、T A 、T S The maximum value in Min(T C ,T A ,T S ) refers to T C 、T A 、T S The minimum value in .

[0077] In some embodiments of the present application, the peel force F1 between the negative electrode sheet and the separator is 15 N / m to 50 N / m. For example, the peel force F1 can be 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, 40 N / m, 45 N / m, 50 N / m, or a range consisting of any two values therebetween. A peel force F1 between the negative electrode sheet and the separator within the above range indicates good adhesion between the negative electrode sheet and the separator. During the charge and discharge process of the secondary battery, the negative electrode sheet and the separator are not easily lost in adhesion, which is beneficial to improving the interface problems between the negative electrode sheet and the separator and the cycle performance of the secondary battery.

[0078] In some embodiments of the present application, the peeling force F2 between the positive electrode sheet and the separator is 11N / m to 45N / m. For example, the peeling force F2 can be a range consisting of any two values between 11N / m, 15N / m, 20N / m, 25N / m, 30N / m, 35N / m, 40N / m, and 45N / m. The peeling force F2 between the positive electrode sheet and the separator is within the above range, indicating that the positive electrode sheet and the separator have good adhesion. During the charge and discharge process of the secondary battery, the positive electrode sheet and the separator are not easy to lose adhesion, which is beneficial to improving the interface problem between the positive electrode sheet and the separator and the cycle performance of the secondary battery.

[0079] In some embodiments of the present application, the first oligomer, the second oligomer, and the third oligomer each independently include at least one of the following functional groups: -COO-, -O-CO-O-, -SO2O-, -PO4, -COOH, -SO2-, -SO-, -CONH2-, -CN, -O-, or -OBO-. When the first oligomer, the second oligomer, and the third oligomer include the above functional groups, it is beneficial to the dissociation of electrolyte salts such as lithium salts in the electrolyte, which is beneficial to improving the ionic conductivity of the electrolyte, and further beneficial to maintaining good kinetic performance while improving the interface problems during the charge and discharge process of the secondary battery and improving the cycle performance of the secondary battery. In addition, the first oligomer, the second oligomer, and the third oligomer have the same repeating unit, so that the first oligomer, the second oligomer, and the third oligomer also have the same functional group.

[0080] A second aspect of the present application provides a method for preparing a secondary battery in any of the above embodiments, comprising the following steps:

[0081] (1) obtaining an electrolyte, the electrolyte comprising a monomer, a fluorinated organic compound, a solvent, and an electrolyte salt, the monomer comprising a first monomer and a second monomer; the first monomer comprising at least one of an acrylate monomer, a carbonate monomer, a sulfate monomer, a sulfonate monomer, a phosphate monomer, a carboxylate monomer, a sulfone monomer, an amide monomer, a nitrile monomer, or an ether monomer; the second monomer comprising at least one of an acrylate monomer, an amide monomer, or a borate monomer; the fluorinated organic compound comprising at least one of a fluorinated carbonate, a fluorinated carboxylate, a fluorinated linear ether, a fluorinated cyclic ether, a fluorinated sulfone compound, a fluorinated phosphide, or a fluorinated carbamate;

[0082] (2) Injecting an electrolyte into a housing provided with an electrode assembly to initiate polymerization of monomers, and obtaining a secondary battery after the polymerization is completed; wherein the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator.

[0083] In the above preparation method, the electrolyte is injected into the shell, and the electrolyte will infiltrate the positive electrode material layer of the positive electrode sheet, the negative electrode material layer of the negative electrode sheet and the separator in the electrode assembly, and then trigger the first monomer and the second monomer to undergo in situ polymerization in the positive electrode material layer, the negative electrode material layer and the separator, generating a first oligomer in the positive electrode material layer, a second oligomer in the negative electrode material layer, and a third oligomer in the separator. During the in situ polymerization process, due to the differences in porosity and pore size of the separator, the positive electrode material layer and the negative electrode material layer, the polymerization degree of the first oligomer, the second oligomer and the third oligomer formed by in situ polymerization is different. At the same time, since the monomers participating in the in situ polymerization in the separator, the positive electrode material layer and the negative electrode material layer are the same, the repeating units of the above oligomers obtained are the same. The types of the first oligomer, the second oligomer and the third oligomer vary with the types of monomers added. It can be understood that the molecular weight of the polymer generated by in situ polymerization is usually small, and this application refers to it as an oligomer.

[0084] Furthermore, during the secondary battery preparation process, the electrolyte essentially infiltrates the positive electrode material layer, the negative electrode material layer, and the interior of the separator. After initiating monomer polymerization, the resulting second oligomer is present not only in the surface region of the negative electrode material layer close to the separator along its thickness, but also in the interior region of the negative electrode material layer away from the separator along its thickness. This ensures that the bonding between the negative electrode material layer and the separator is not limited to the surface of the negative electrode material layer, but also acts within the interior of the negative electrode material layer. Consequently, when the negative electrode material undergoes volumetric changes during the secondary battery's charge and discharge process, the negative electrode plate is less likely to lose adhesion to the separator, thereby improving the interface between the negative electrode plate and the separator and the secondary battery's cycling performance. Similarly, the first oligomer is also present in both the surface and interior regions of the positive electrode material layer, making it less likely that the positive electrode plate will lose adhesion to the separator, thereby improving the interface between the positive electrode plate and the separator and the secondary battery's cycling performance. Furthermore, taking the negative electrode material layer as an example, in-situ polymerization in the negative electrode material layer and in-situ polymerization in the separator can proceed simultaneously, with the generated second and third oligomers penetrating each other, strengthening the interaction between the negative electrode material layer and the separator, and thus achieving good adhesion between the negative electrode plate and the separator in the resulting secondary battery. Similarly, during the in-situ polymerization process, the first and third oligomers penetrating each other also achieve good adhesion between the positive electrode plate and the separator. As a result, the secondary battery provided by this application improves interfacial issues and cycle performance during the charge and discharge cycle.

[0085] In some embodiments of the present application, the porosity of the diaphragm after being soaked in dimethyl carbonate for 1 minute is P1, and the porosity of the diaphragm after being soaked in dimethyl carbonate for 15 minutes is P2, and 1≤P2 / P1≤1.55. In some embodiments of the present application, 1≤P2 / P1≤1.25. For example, P2 / P1 can be 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55 or a range consisting of any two values therebetween. P2 / P1 is within the above range, that is, the porosity of the diaphragm changes before and after being soaked in dimethyl carbonate, indicating that the substances present in the pores in the diaphragm are dissolved during the soaking process. At the same time, the molecular weight of the oligomers generated by in situ polymerization is usually small and can be dissolved in dimethyl carbonate, indicating that the third oligomer generated by in situ polymerization is present in the diaphragm. In the present application, P1 and P2 are the porosities of separators disassembled from secondary batteries after being immersed in dimethyl carbonate.

[0086] In this application, after the separator is soaked in dimethyl carbonate for 15 minutes, the third oligomer is substantially dissolved. Therefore, the porosity of the separator after soaking is substantially equivalent to the porosity of the separator itself. In some embodiments of this application, the porosity of the separator itself is 60% to 95%, with 60% ≤ P2 ≤ 95%. In this application, the porosity of the separator itself refers to the porosity of the separator itself before assembly into a secondary battery.

[0087] In some embodiments of the present application, the positive electrode sheet, the negative electrode sheet and the diaphragm include fluorinated organic matter, and the fluorinated organic matter includes at least one of fluorinated carbonates, fluorinated carboxylates, fluorinated linear ethers, fluorinated cyclic ethers, fluorinated sulfone compounds, fluorinated phosphides or fluorinated carbamates. The electronegativity of the above-mentioned types of fluorinated organic matter is relatively strong, and the fluorine atoms or fluorinated functional groups therein can form van der Waals forces with the molecular weight, which is conducive to increasing the force between the molecular chains and reducing the crystallinity of the molecular chains, so that a network-like connection can be formed between the molecular chains, thereby improving the adhesion between the positive electrode sheet and the diaphragm, and the negative electrode sheet and the diaphragm, and further improving the interface problems and cycle performance during the cycle. In the present application, the above-mentioned fluorinated organic matter can be added when preparing the electrolyte of the secondary battery. When the electrolyte infiltrates the positive electrode sheet, the negative electrode sheet and the diaphragm, it contains the above-mentioned fluorinated organic matter.

[0088] In some embodiments of the present application, the fluorocarbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, monofluoropropylene carbonate, trifluoropropylene carbonate, 4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]-dioxane-2-one, 4-(2,3,3,3-tetrafluoro-2-trifluoromethylpropyl)-[1,3]dioxane-2-one, 2,2,2-trifluoroethyl methyl carbonate, 2,2-difluoroethyl ethyl carbonate, ethyl (2,2,2-trifluoroethyl) carbonate, ethyl (1-fluoroethyl) carbonate or 2,2,2-trifluoroethyl (1-fluoroethyl) carbonate. In some embodiments of the present application, the fluorocarbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, trifluoropropylene carbonate, 2,2,2-trifluoroethyl methyl carbonate, 2,2-difluoroethyl ethyl carbonate, or ethyl (2,2,2-trifluoroethyl) carbonate.

[0089] In some embodiments of the present application, the fluorocarboxylic acid ester includes at least one of α-fluoro γ-butyrolactone, β-fluoro γ-butyrolactone, methyl trifluoroacetate, ethyl trifluoroacetate, 2-fluoroethyl acetate, ethyl fluoroacetate, 2,2,2-trifluoroacetic acid methyl ester, 2,2-difluoroacetic acid methyl ester, 2,2,2-trifluoroacetic acid ethyl ester, 2,2,2-trifluoroacetic acid propyl ester, 2,2,2-trifluoroacetic acid butyl ester or 2,2,2-trifluoroacetic acid hexyl ester. In some embodiments of the present application, the fluorocarboxylic acid ester includes at least one of α-fluoro γ-butyrolactone, methyl trifluoroacetate, ethyl trifluoroacetate, 2-fluoroethyl acetate, 2,2,2-trifluoroacetic acid methyl ester or 2,2-difluoroacetic acid methyl ester.

[0090] In some embodiments of the present application, the fluorinated linear ether includes at least one of fluorinated 1,2-diethoxyethane, difluoro 1-ethoxy-2-methoxyethane, trifluoro 1-ethoxy-2-methoxyethane, fluorinated 1,2-diethoxyethane, difluoro 1,2-diethoxyethane, trifluoro 1,2-diethoxyethane, tetrafluoro 1,2-diethoxyethane, tetrafluoro 1,2-diethoxyethane, pentafluoro 1,2-diethoxyethane, or hexafluoro 1,2-diethoxyethane. In some embodiments of the present application, the fluorinated linear ether includes at least one of fluorinated 1,2-diethoxyethane, difluoro 1-ethoxy-2-methoxyethane, trifluoro 1-ethoxy-2-methoxyethane, or tetrafluoro 1,2-diethoxyethane.

[0091] In some embodiments of the present application, the fluorinated cyclic ether includes at least one of 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane or 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane.

[0092] In some embodiments of the present application, the fluorinated sulfone compound includes at least one of 3,3,3-trifluoropropyl methyl sulfone, 3-fluoro-1,3-propane sultone, 2-fluorotetrahydrothiophene-1,1-dioxide, 3-fluorotetrahydrothiophene-1,1-dioxide, trifluoromethyl isopropyl sulfone, or trifluoromethyl propyl methyl sulfone. In some embodiments of the present application, the fluorinated sulfone compound includes at least one of 3,3,3-trifluoropropyl methyl sulfone or trifluoromethyl isopropyl sulfone.

[0093] In some embodiments of the present application, the fluorinated phosphide includes at least one of tris(2,2,2-trifluoroethyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane-2-oxide, 2-(2,2,3,3,3-pentafluoropropoxy)-1,3,2-dioxaphospholane or 2-(2,2,3,3,3-pentafluoropropoxy)-4-(trifluoromethyl)-1,3,2-dioxaphospholane. In some embodiments of the present application, the fluorinated phosphide includes at least one of tris(2,2,2-trifluoroethyl)phosphate or tris(2,2,2-trifluoroethyl)phosphate.

[0094] In some embodiments of the present application, the fluorocarbamate includes at least one of 2,2,2-trifluoroethyl-N,N-dimethylcarbamate, 1,1,1,3,3,3-hexafluoropropyl-N,N-dimethylcarbamate, 2,2,2-trifluoroethyl-N,N-diethylcarbamate, or 1,1,1,3,3,3-hexafluoropropyl-N,N-diethylcarbamate. In some embodiments of the present application, the fluorocarbamate includes at least one of 2,2,2-trifluoroethyl-N,N-dimethylcarbamate, 1,1,1,3,3,3-hexafluoropropyl-N,N-dimethylcarbamate, or 2,2,2-trifluoroethyl-N,N-diethylcarbamate.

[0095] In some embodiments of the present application, the negative electrode material layer includes a silicon material; based on the mass of the negative electrode material layer, the mass percentage of the silicon element is W1; in a thermogravimetric analysis (TG) test of the negative electrode material layer, the weight loss rate of the negative electrode material layer between 90°C and 180°C is m; 0.01≤100m / W1≤0.1. For example, 100m / W1 can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a range consisting of any two values therebetween. Silicon materials generally undergo large volume changes during charge and discharge, and the greater the silicon content in the negative electrode material layer, the greater the volume change produced, which tends to increase the gap between the negative electrode material layer and the separator, thereby affecting the cycle performance of the secondary battery. Therefore, when the silicon content in the negative electrode material layer is greater, the bonding between the negative electrode material layer and the separator should also be better. The weight loss rate of the negative electrode material layer between 90°C and 180°C in the TG test corresponds to the mass percentage of the second oligomer in the negative electrode material layer. A higher content of the second oligomer in the negative electrode material layer improves the bonding network formed within the negative electrode material layer and between the negative electrode material layer and the separator. Therefore, regulating 100m / W1 within the above range ensures a better match between the silicon content in the negative electrode material layer and the bonding network within the negative electrode material layer and between the negative electrode material layer and the separator. This reduces the negative electrode plate's ability to lose adhesion to the separator during the secondary battery's charge and discharge process, as the negative electrode material undergoes volume changes. This improves the interface between the negative electrode plate and the separator, as well as the secondary battery's cycling performance.

[0096] In this application, the thermal weight loss rate refers to the ratio of the mass loss caused by decomposition, volatilization or other chemical reactions of the material in the negative electrode material layer during heating to the original mass.

[0097] In some embodiments of the present application, 5%≤W1≤80%. For example, W1 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range consisting of any two values therebetween. The present application has no particular restrictions on the type of silicon material, as long as the purpose of the present application can be achieved. For example, the silicon material can include but is not limited to elemental silicon, silicon-carbon composite materials or SiO x At least one of the following, wherein 0<X<2. In some embodiments of the present application, the silicon material comprises a silicon-carbon composite material. In some embodiments of the present application, the silicon material comprises elemental silicon.

[0098] In some embodiments of the present application, based on the mass of the negative electrode material layer, the mass percentage of the silicon material is 10% to 90%.

[0099] In some embodiments of the present application, the negative electrode plate includes a negative electrode material layer, wherein the thickness of the negative electrode material layer is H μm; in a thermogravimetric analysis test of the negative electrode material layer, the weight loss rate of the negative electrode material layer between 90°C and 180°C is m; and 0.6≤m / H×100≤6.3. For example, m / H×100 can be 0.6, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.3, or a range consisting of any two values therebetween. The thicker the negative electrode material layer, the higher the total silicon content. By regulating m / H×100 within the above range, the total silicon content in the negative electrode material layer is more closely aligned with the bonding network within the negative electrode material layer and between the negative electrode material layer and the separator. During the charge and discharge process of the secondary battery, when the negative electrode material undergoes volume changes, the negative electrode plate is less likely to lose adhesion with the separator, thereby improving the interface problem between the negative electrode plate and the separator and the cycle performance of the secondary battery.

[0100] In some embodiments of the present application, 20≤H≤120. For example, H can be 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, or a range consisting of any two values therebetween.

[0101] In some embodiments of the present application, the positive electrode material layer includes a positive electrode binder. Based on the mass of the positive electrode material layer, the mass percentage of the positive electrode binder is W2, 0.5%≤W2≤3.0%; for example, the mass percentage of the positive electrode binder W2 can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2.0%, 2.5%, 3.0%, or a range consisting of any two values therebetween. Due to the presence of the in-situ polymerized first oligomer in the positive electrode material layer, which permeates the interior of the positive electrode material layer, it is beneficial to improve the bonding network within the positive electrode material layer. Therefore, the content of the positive electrode binder in the positive electrode material layer can be reduced accordingly, so that the positive electrode material layer and the separator still have good adhesion. At the same time, the reduction in the positive electrode binder content is beneficial to improving the energy density of the secondary battery. Therefore, by regulating the mass percentage of the positive electrode binder within the above range, while improving the interface problem between the positive electrode sheet and the separator and the cycle performance of the secondary battery, it is also beneficial to take into account the energy density of the secondary battery.

[0102] In some embodiments of the present application, the negative electrode material layer includes a negative electrode binder, and based on the mass of the negative electrode material layer, the mass percentage of the negative electrode binder is W3, 2%≤W3≤10%. For example, the mass percentage of the negative electrode binder W3 can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two values therebetween. Since there is an in-situ polymerized first oligomer in the negative electrode material layer, it penetrates into the interior of the negative electrode material layer, which is beneficial to improving the bonding network inside the negative electrode material layer. Therefore, the content of the negative electrode binder in the negative electrode material layer can be reduced accordingly, so that the negative electrode material layer and the separator still have good bonding. At the same time, the reduction in the negative electrode binder content is beneficial to improving the energy density of the secondary battery. Therefore, by regulating the mass percentage of the negative electrode binder within the above range, while improving the interface problem between the negative electrode sheet and the separator and the cycle performance of the secondary battery, it is also beneficial to take into account the energy density of the secondary battery.

[0103] In some embodiments of the present application, 0.5% ≤ W2 ≤ 3.0%, and 2% ≤ W3 ≤ 10%. Thus, by regulating the mass percentages of the positive electrode binder and the negative electrode binder within the above ranges, the interface problems between the positive electrode sheet and the separator, the interface problems between the negative electrode sheet and the separator, and the cycle performance of the secondary battery are improved while also balancing the energy density of the secondary battery.

[0104] In the present application, the positive electrode material layer may further include a conductive agent. The present application has no particular restrictions on the conductive agent, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers, and conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers, and specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0105] In the present application, the positive electrode sheet also includes a positive electrode current collector, and the positive electrode material layer is 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 can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the positive electrode current collector surface or a partial area of the positive electrode current collector surface. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0106] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0107] The positive electrode material layer includes a positive electrode active material. The present application has no particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

[0108] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0109] In the present application, the negative electrode material layer may further include a conductive agent. The present application has no particular limitation on the type of the conductive agent, as long as the purpose of the present application can be achieved. For example, it may be at least one of the above-mentioned conductive agents.

[0110] In the present application, the negative electrode sheet also includes a negative electrode current collector, and the negative electrode material layer is disposed on at least one surface of the negative electrode current collector. The phrase "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 can be disposed on one surface of the negative electrode current collector along its thickness direction, or on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can refer to the entire surface of the negative electrode current collector or a portion of the surface of the negative electrode current collector. This is not particularly limited in the present application, as long as the purpose of this application can be achieved.

[0111] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector. For example, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0112] The present application does not particularly limit the thickness of the negative electrode material layer, as long as it can achieve the purpose of the present application. For example, the thickness of the negative electrode material layer is 20 μm to 120 μm. The present application does not particularly limit the thickness of the negative electrode current collector, as long as it can achieve the purpose of the present application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0113] The present application does not particularly limit the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane, or a spun membrane.

[0114] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven 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 film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0115] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0116] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The application is not particularly limited to inorganic particles. For example, inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The application is not particularly limited to the binder. For example, the binder can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0117] In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0118] The third aspect of the present application further provides a method for preparing a secondary battery in any of the aforementioned embodiments, comprising the following steps:

[0119] (1) An electrolyte solution is obtained, wherein the electrolyte solution includes a monomer, a solvent, and an electrolyte salt, and the monomer includes a first monomer and a second monomer.

[0120] In some embodiments of the present application, the weight percentage content W4 of the monomer is 2% to 80% based on the weight of the electrolyte; in some embodiments of the present application, 3% ≤ W4 ≤ 50%. For example, the weight percentage content W4 of the monomer can be 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range consisting of any two values therebetween.

[0121] In some embodiments of the present application, based on the total mass of the monomers, the mass percentage content W41 of the first monomer is 1% to 99%; for example, the mass percentage content W41 of the first monomer can be 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99% or a range consisting of any two values therebetween. In some embodiments of the present application, based on the total mass of the monomers, the mass percentage content W42 of the second monomer is 1% to 99%; for example, the mass percentage content W42 of the second monomer can be 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99% or a range consisting of any two values therebetween.

[0122] The first monomer includes at least one of an acrylate monomer, a carbonate monomer, a sulfate monomer, a sulfonate monomer, a phosphate monomer, a carboxylate monomer, a sulfone monomer, an amide monomer, a nitrile monomer or an ether monomer; the second monomer includes at least one of an acrylate monomer, an amide monomer or a borate monomer.

[0123] (2) Injecting an electrolyte into a housing provided with an electrode assembly to initiate polymerization of monomers, and obtaining a secondary battery after the polymerization is completed; wherein the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator.

[0124] The preparation method provided herein initiates in-situ polymerization of a first monomer and a second monomer, allowing the resulting second and third oligomers to interpenetrate each other, thereby strengthening the interaction between the negative electrode material layer and the separator. Similarly, the interpenetration of the first and third oligomers strengthens the interaction between the positive electrode plate and the separator. This improves the adhesion between the positive electrode plate and the separator, and between the negative electrode plate and the separator. When the monomer content in the electrolyte is too low, for example, less than 2%, the electrolyte contains relatively little monomer, and the first, second, and third oligomers generated by in-situ polymerization have little effect on improving the adhesion between the positive electrode plate and the separator, and between the negative electrode plate and the separator. When the monomer content in the electrolyte is too high, for example, greater than 80%, the in-situ polymerization produces a high content of the first, second, and third oligomers, which can affect the transport of active ions, such as lithium ions, and thus the rate performance of the secondary battery, exacerbating interfacial issues. Thus, by regulating the mass percentage of the monomer in the electrolyte and the mass percentage of the first monomer and the second monomer in the monomer within the above range, and selecting the above-mentioned types of first monomer and second monomer, in the secondary battery obtained after in situ polymerization, the positive electrode sheet, the negative electrode sheet and the separator can form a whole, so that there is good adhesion between the positive electrode sheet and the separator, and between the negative electrode sheet and the separator, which is beneficial to improving the interface problems in the secondary battery cycle process and improving its cycle performance.

[0125] The present application does not particularly limit the method of initiating monomer polymerization, as long as the purpose of the present application can be achieved. For example, the method of initiating monomer polymerization may include but is not limited to initiator initiation, photoinitiation or electron beam irradiation initiation. The temperature of the initiator-induced polymerization can be 45°C to 80°C, and the initiator can be but is not limited to at least one of azobisisobutyronitrile, dibenzoyl peroxide, cyclohexylenebis[(1,1-dimethylpropyl)] peroxide or di-tert-amyl peroxide. Based on the total mass of the monomer, the mass percentage of the initiator can be 0.5% to 5%; the light power density of the photoinitiated polymerization is 2W / cm 2 Up to 5W / cm 2 , the photoinitiated polymerization time is 10s to 300s; the total electron beam irradiation dose is 40Gy to 40000Gy.

[0126] In the present application, after monomer polymerization, at least a portion of the electrolyte is converted into a gel-state electrolyte. It is understood that in a secondary battery, active ions can be transported by a fluid electrolyte or by a gel-state electrolyte. In some embodiments of the present application, 2% ≤ W4 ≤ 4%, and the active ions in the secondary battery are primarily transported by a fluid electrolyte. In some embodiments of the present application, 4% < W4 ≤ 80%, and the active ions in the secondary battery are primarily transported by a gel-state electrolyte.

[0127] In some embodiments of the present application, the carbonate monomer includes at least one of vinyl ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate or chloroethylene carbonate. The above-mentioned carbonate monomer is conducive to improving the adhesion between the positive electrode plate and the diaphragm, and the adhesion between the negative electrode plate and the diaphragm, and has little effect on the dynamic performance, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the carbonate monomer includes at least one of vinyl ethylene carbonate or propylene carbonate. The above-mentioned carbonate monomer can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0128] In some embodiments of the present application, the sulfate ester monomer includes at least one of vinyl vinyl sulfite, vinyl sulfite, 4-methyl vinyl sulfate or 4-ethyl vinyl sulfate. The above-mentioned sulfate ester monomer is beneficial to improving the adhesion between the positive electrode plate and the diaphragm, and the adhesion between the negative electrode plate and the diaphragm, and has little effect on the kinetic performance, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the sulfate ester monomer includes at least one of vinyl vinyl sulfite or vinyl sulfite. The above-mentioned sulfate ester monomer can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0129] In some embodiments of the present application, the sulfonate monomer includes at least one of 1,3-propylene sultone, 1,4-butane sulfonate or methylene disulfonate. The above-mentioned sulfonate monomer is conducive to improving the adhesion between the positive electrode plate and the diaphragm, and the adhesion between the negative electrode plate and the diaphragm, and has little effect on the kinetic performance, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the sulfonate monomer includes at least one of 1,3-propylene sultone or 1,4-butane sulfonate. The above-mentioned sulfonate monomer can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0130] In some embodiments of the present application, the phosphate monomer includes at least one of dimethyl vinyl phosphate, triethyl vinyl phosphate, diethyl propenyl phosphate, triethyl butenyl phosphate, diethyl (I)-buten-2-yl phosphonate, diethyl ethynyl phosphate, vinyl trifluoromethyl phosphate, vinyl-1-trifluoroethyl phosphate, diethyl fluorovinyl phosphate or 1-trifluoropropenylethyl phosphate. The above-mentioned phosphate monomer is beneficial to improve the adhesion between the positive electrode and the diaphragm, the adhesion between the negative electrode and the diaphragm, and has little effect on the kinetic performance, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the phosphate monomer includes at least one of dimethyl vinyl phosphate, triethyl vinyl phosphate, diethyl propenyl phosphate, vinyl-1-trifluoroethyl phosphate or diethyl fluorovinyl phosphate. The above-mentioned phosphate monomer can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0131] In some embodiments of the present application, the carboxylate monomer includes vinyl acetate. This carboxylate monomer is beneficial for improving the adhesion between the positive electrode plate and the separator, and between the negative electrode plate and the separator, and has little effect on the dynamic performance, thereby improving the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0132] In some embodiments of the present application, the sulfone monomer includes at least one of methyl vinyl sulfone, ethyl vinyl sulfone, cyclobutane sulfone, cyclopentane sulfone or ethylene sulfoxide. The above-mentioned sulfone monomers are beneficial to improving the adhesion between the positive electrode plate and the diaphragm, and the adhesion between the negative electrode plate and the diaphragm, and have little effect on the kinetic performance, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the sulfone monomer includes at least one of methyl vinyl sulfone, cyclopentane sulfone or cyclopentane sulfoxide. The above-mentioned sulfone monomers can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0133] In some embodiments of the present application, the amide monomer includes acrylamide. Such amide monomers are beneficial for improving the adhesion between the positive electrode plate and the separator, and between the negative electrode plate and the separator, and have little effect on the dynamic performance, thereby improving the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0134] In some embodiments of the present application, the nitrile monomer includes at least one of acrylonitrile, succinonitrile, glutaronitrile or adiponitrile. The above-mentioned nitrile monomer monomer is conducive to improving the adhesion between the positive electrode plate and the diaphragm, the adhesion between the negative electrode plate and the diaphragm, and has little effect on the kinetic performance, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the nitrile monomer includes at least one of acrylonitrile, succinonitrile, glutaronitrile or adiponitrile. The above-mentioned nitrile monomer monomer can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0135] In some embodiments of the present application, the ether monomer includes at least one of 1,3-dioxolane, ethylene oxide, 1,2-propylene oxide, 4-methyl-1,3-dioxolane tetrahydrofuran, 2-methyltetrahydrofuran, 14-dioxane, ethylene glycol dimethyl ether, ethylene glycol diglycidyl ether or triethylene glycol divinyl ether. The above-mentioned ether monomers are beneficial to improving the adhesion between the positive electrode plate and the diaphragm, and the adhesion between the negative electrode plate and the diaphragm, and have little effect on the kinetic performance, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the ether monomer includes at least one of 1,3-dioxolane, ethylene oxide or 1,2-propylene oxide. The above-mentioned ether monomers can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0136] In some embodiments of the present application, the acrylate monomers include acrylic acid, methacrylic acid, methyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, butyl acrylate, isodecyl acrylate, isooctyl acrylate, lauryl acrylate, isobornyl acrylate, isobornyl methacrylate, ethoxyethoxyethyl acrylate, cyanoacrylate, caprolactone acrylate, 2-phenoxyethyl acrylate, tetrahydrofuran acrylate, ethyltetrahydrofuran acrylate, cyclotrimethylolpropane acrylate, 2-carboxyethyl acrylate, cyclohexyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, triethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dioctanoate, tetraethylene glycol dimethacrylate. , 1,4-butanediol diacrylate, 1-4-butanediol dimethacrylate, 1,3-butanediol triacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, tripropylene glycol diacrylate, dipropylene glycol dimethacrylate, tripropylene glycol diacrylate, tripropylene glycol dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, 2 (propoxylated) neopentyl glycol diacrylate, methoxy polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, methoxy polyethylene glycol methacrylate, pentaerythritol triacrylate, propoxylated glycerol triacrylate, tris(2-hydroxyethyl)isocyanuric acid triacrylate, di(trimethylolpropane) tetraacrylate or at least one of pentaerythritol tetraacrylate. The above-mentioned acrylic acid ester monomers are beneficial to improving the adhesion between the positive electrode plate and the separator, and the adhesion between the negative electrode plate and the separator, and have little effect on the dynamic performance, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the acrylate monomer includes at least one of methyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1-4-butanediol dimethacrylate, 1,3-butanediol triacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, propoxylated glycerol triacrylate, di(trimethylolpropane) tetraacrylate or pentaerythritol tetraacrylate. The above-mentioned acrylate monomers can better improve the interface problems and cycle performance of secondary batteries during charge and discharge cycles.Wherein, butyl methacrylate can be n-butyl methacrylate and / or isobutyl methacrylate. In the present application, propylene glycol dimethacrylate is also 1,3-propylene glycol dimethacrylate.

[0137] In some embodiments of the present application, the borate monomer includes at least one of phenyl borate, methyl borate, ethyl borate, benzyl borate or 4-fluorophenyl borate. The above-mentioned borate monomers are beneficial to improving the adhesion between the positive electrode plate and the diaphragm, and the adhesion between the negative electrode plate and the diaphragm, and have little effect on the kinetic performance, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the borate monomer includes at least one of methyl borate or ethyl borate. The above-mentioned borate monomers can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0138] In some embodiments of the present application, the electrolyte further includes a fluorinated organic compound, wherein the fluorinated organic compound includes at least one of a fluorinated carbonate, a fluorinated carboxylate, a fluorinated linear ether, a fluorinated cyclic ether, a fluorinated sulfone compound, a fluorinated phosphide, or a fluorinated carbamate. In some embodiments of the present application, the mass percentage content W5 of the fluorinated organic compound is 1% to 30% based on the mass of the electrolyte. In some embodiments of the present application, 2% ≤ W5 ≤ 20%. For example, the mass percentage content W5 of the fluorinated organic compound can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, or a range consisting of any two values therebetween. After the electrolyte infiltrates the positive electrode sheet, negative electrode sheet, and separator, the positive electrode sheet, negative electrode sheet, and separator contain the aforementioned fluorinated organic compound. The aforementioned fluorinated organic compound has a strong electronegativity, and the fluorine atoms or fluorinated functional groups therein can form van der Waals forces with the molecular chains, which helps to increase the interaction between the molecular chains and reduce the crystallinity of the molecular chains, allowing the molecular chains to form a network-like connection, thereby improving the adhesion between the positive electrode sheet and the separator, and between the negative electrode sheet and the separator, and further improving the interface problems and cycle performance during the cycle. By regulating the mass percentage of the fluorinated organic compound within the above range, it is also possible to take into account the dynamics and further improve the interface problems of the secondary battery during the charge and discharge cycle.

[0139] In some embodiments of the present application, the fluorocarbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, monofluoropropylene carbonate, trifluoropropylene carbonate, 4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]-dioxane-2-one, 4-(2,3,3,3-tetrafluoro-2-trifluoromethylpropyl)-[1,3]dioxane-2-one, 2,2,2-trifluoroethyl methyl carbonate, 2,2-difluoroethyl ethyl carbonate, ethyl (2,2,2-trifluoroethyl) carbonate, ethyl (1-fluoroethyl) carbonate or 2,2,2-trifluoroethyl (1-fluoroethyl) carbonate. The above-mentioned fluorinated carbonate has a suitable electronegativity, so that a network-like connection can be formed between the molecular chains, thereby improving the adhesion between the positive electrode sheet and the diaphragm, and the negative electrode sheet and the diaphragm while taking into account the dynamic performance; at the same time, it can also participate in the formation of a solid electrolyte membrane (SEI membrane) with stable performance to protect the negative electrode material layer, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the fluorinated carbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, trifluoropropylene carbonate, 2,2,2-trifluoroethyl methyl carbonate, 2,2-difluoroethyl ethyl carbonate or ethyl (2,2,2-trifluoroethyl) carbonate. The above-mentioned fluorinated carbonate can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0140] In some embodiments of the present application, the fluorocarboxylic acid ester includes at least one of α-fluoroγ-butyrolactone, β-fluoroγ-butyrolactone, methyl trifluoroacetate, ethyl trifluoroacetate, ethyl 2-fluoroacetate, ethyl fluoroacetate, methyl 2,2,2-trifluoroacetate, methyl 2,2-difluoroacetate, ethyl 2,2,2-trifluoroacetate, propyl 2,2,2-trifluoroacetate, butyl 2,2,2-trifluoroacetate, or hexyl 2,2,2-trifluoroacetate. These fluorocarboxylic acid esters have suitable electronegativity, allowing for the formation of a network-like connection between the molecular chains, improving the adhesion between the positive electrode and the separator, and between the negative electrode and the separator, while also taking into account the kinetic performance. They can also participate in the formation of a stable SEI film to protect the negative electrode material layer, thereby improving the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the fluorocarboxylate includes at least one of α-fluoroγ-butyrolactone, methyl trifluoroacetate, ethyl trifluoroacetate, ethyl 2-fluoroacetate, methyl 2,2,2-trifluoroacetate, or methyl 2,2-difluoroacetate. These fluorocarboxylates can improve interfacial issues and cycle performance of secondary batteries during charge and discharge cycles.

[0141] In some embodiments of the present application, the fluorinated linear ether includes at least one of fluorinated 1,2-diethoxyethane, difluoro 1-ethoxy-2-methoxyethane, trifluoro 1-ethoxy-2-methoxyethane, fluorinated 1,2-diethoxyethane, difluoro 1,2-diethoxyethane, trifluoro 1,2-diethoxyethane, tetrafluoro 1,2-diethoxyethane, tetrafluoro 1,2-diethoxyethane, pentafluoro 1,2-diethoxyethane, or hexafluoro 1,2-diethoxyethane. The fluorinated linear ether has a suitable electronegativity, allowing for a network-like connection between the molecular chains, thereby improving the adhesion between the positive electrode sheet and the separator, and between the negative electrode sheet and the separator, while also taking into account the kinetic performance. It can also participate in the formation of a stable SEI film to protect the negative electrode material layer, thereby improving the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the fluorinated linear ether includes at least one of fluorinated 1,2-diethoxyethane, difluoro-1-ethoxy-2-methoxyethane, trifluoro-1-ethoxy-2-methoxyethane, or tetrafluoro-1,2-diethoxyethane. These fluorinated linear ethers can better improve interfacial issues and cycle performance of secondary batteries during charge and discharge cycles.

[0142] In some embodiments of the present application, the fluorinated cyclic ether includes at least one of 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane or 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane. These fluorinated cyclic ethers have suitable electronegativity, allowing for a network-like connection between the molecular chains, improving the adhesion between the positive electrode and the separator, and between the negative electrode and the separator, while also taking into account dynamic performance. They can also participate in the formation of a stable SEI film to protect the negative electrode material layer, thereby improving interfacial issues and cycle performance of the secondary battery during the charge and discharge cycle.

[0143] In some embodiments of the present application, the fluorinated sulfone compound includes at least one of 3,3,3-trifluoropropyl methyl sulfone, 3-fluoro-1,3-propane sultone, 2-fluorotetrahydrothiophene-1,1-dioxide, 3-fluorotetrahydrothiophene-1,1-dioxide, trifluoromethyl isopropyl sulfone, or trifluoromethyl propyl methyl sulfone. The above-mentioned fluorinated sulfone compounds have suitable electronegativity, so that the molecular chains can form a network-like connection, improving the adhesion between the positive electrode plate and the separator, and the negative electrode plate and the separator while taking into account the dynamic performance; at the same time, they can also participate in the formation of a stable SEI film to protect the negative electrode material layer, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the fluorinated sulfone compound includes at least one of 3,3,3-trifluoropropyl methyl sulfone or trifluoromethyl isopropyl sulfone. The above-mentioned fluorinated sulfone compounds can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle.

[0144] In some embodiments of the present application, the fluorinated phosphide includes at least one of tris(2,2,2-trifluoroethyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane-2-oxide, 2-(2,2,3,3,3-pentafluoropropoxy)-1,3,2-dioxaphospholane, or 2-(2,2,3,3,3-pentafluoropropoxy)-4-(trifluoromethyl)-1,3,2-dioxaphospholane. The above-mentioned fluorinated phosphide has a suitable electronegativity, so that a network-like connection can be formed between the molecular chains, thereby improving the adhesion between the positive electrode sheet and the separator, and between the negative electrode sheet and the separator while taking into account the dynamic performance; at the same time, it can also participate in the formation of a stable SEI film to protect the negative electrode material layer, thereby helping to improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the fluorinated phosphide includes at least one of tris(2,2,2-trifluoroethyl)phosphate or tris(2,2,2-trifluoroethyl)phosphate. The above fluorinated phosphide can better improve the interface problems and cycle performance of the secondary battery during the charge and discharge cycle process.

[0145] In some embodiments of the present application, the fluorocarbamate includes at least one of 2,2,2-trifluoroethyl-N,N-dimethylcarbamate, 1,1,1,3,3,3-hexafluoropropyl-N,N-dimethylcarbamate, 2,2,2-trifluoroethyl-N,N-diethylcarbamate, or 1,1,1,3,3,3-hexafluoropropyl-N,N-diethylcarbamate. These fluorocarbamates have suitable electronegativity, allowing for the formation of a network of connections between the molecular chains, improving the adhesion between the positive electrode and the separator, and between the negative electrode and the separator, while also taking into account dynamic performance. They can also participate in the formation of a stable SEI film to protect the negative electrode material layer, thereby improving interfacial issues and cycle performance of the secondary battery during the charge and discharge cycle. In some embodiments of the present application, the fluorocarbamate includes at least one of 2,2,2-trifluoroethyl-N,N-dimethylcarbamate, 1,1,1,3,3,3-hexafluoropropyl-N,N-dimethylcarbamate, or 2,2,2-trifluoroethyl-N,N-diethylcarbamate. These fluorocarbamates can better improve the interfacial problems and cycle performance of secondary batteries during charge and discharge cycles.

[0146] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage W6 of the electrolyte salt is 8% to 15%. For example, the mass percentage W6 of the electrolyte salt can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range consisting of any two values therebetween. The present application does not particularly limit the type of electrolyte salt, as long as the purpose of the present application can be achieved. For example, the lithium salt can include but is not limited to at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (C4BLiO8, abbreviated as LiBOB) or lithium difluoroborate.

[0147] In some embodiments of the present application, the solvent may include but is not limited to at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propyl propionate. Based on the mass of the electrolyte, the mass percentage W7 of the solvent is 0% to 90%.

[0148] In some embodiments of the present application, the electrolyte includes a monomer, a solvent, and an electrolyte salt. Based on the mass of the electrolyte, the mass percentages of the monomer and the electrolyte salt are as described above, and the mass percentage of the solvent is 5% to 90%.

[0149] In some embodiments of the present application, the electrolyte includes monomers, fluorinated organic matter, solvent and electrolyte salt. Based on the mass of the electrolyte, the mass percentages of the monomers, fluorinated organic matter and electrolyte salt are as described above, and the mass percentage of the solvent is 0% to 89%.

[0150] The preparation process of the secondary battery of the present application may also include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, and placing the electrode assembly in a shell. Alternatively, stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, and placing the electrode assembly in a shell. In addition, as needed, anti-overcurrent elements, guide plates, etc. can also be placed in the shell to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0151] In some embodiments of the present application, the secondary battery of the present application may include but is not limited to: a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery or a lithium ion polymer secondary battery, etc. In some embodiments of the present application, the secondary battery includes a lithium ion battery.

[0152] The fourth aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments or the secondary battery prepared by the preparation method in any of the aforementioned embodiments. Thus, the electronic device provided by the present application has good performance.

[0153] The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0154] Example

[0155] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0156] Test methods and equipment:

[0157] sampling:

[0158] After the lithium-ion battery is discharged at 0.5C to the discharge cut-off voltage, it is disassembled in an argon atmosphere, and then the surfaces of the positive electrode sheet, the negative electrode sheet and the diaphragm are wiped separately with dust-free paper, and the electrolyte and / or gel electrolyte on the surface are wiped clean, and then placed in a glove box for 12 hours to obtain samples of the positive electrode sheet, the negative electrode sheet and the diaphragm, and the positive electrode material layer on the surface of the positive electrode sheet is scraped to obtain a sample of the positive electrode material layer powder; the negative electrode material layer on the surface of the negative electrode sheet is scraped to obtain a sample of the negative electrode material layer powder. Unless otherwise specified, the following tests are all tested using the samples obtained above. Among them, the discharge cut-off voltage of the lithium-ion batteries in the embodiments of the present application and the comparative examples is 3.0V. It can be understood that when the voltage range marked on the outer packaging of the factory battery is 3.0V to 4.45V, the charge cut-off voltage is 4.45V and the discharge cut-off voltage is 3.0V.

[0159] DSC test:

[0160] The DSC spectrum of 50 mg of cathode material layer powder was tested using a NETZSCH STA499C thermal analyzer at a heating rate of 5°C / min. The highest peak between 90°C and 180°C was the first thermal decomposition peak, and the temperature corresponding to the peak was T C Replace the positive electrode material layer powder with the negative electrode material layer powder and the separator to obtain T A and T S .

[0161] TG test:

[0162] The TG spectrum of 50 mg of the negative electrode material layer powder was measured using a NETZSCH STA499C thermal analyzer at a heating rate of 10°C / min. The weight loss between 90°C and 180°C is m, while the weight loss between 300°C and 500°C corresponds to the weight loss of the negative electrode binder, or W3.

[0163] The TG spectrum of 50 mg of cathode material layer powder was measured using a NETZSCH STA499C thermal analyzer at a heating rate of 10°C / min. The weight loss between 300°C and 500°C corresponds to the weight loss of the cathode binder, also known as W2.

[0164] Test of the mass percentage of silicon element W1:

[0165] Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to measure the mass percentage of silicon in the negative electrode material layer powder, also known as W1. Prior to testing, the negative electrode sheets obtained from the above sampling were soaked in dimethyl carbonate for 15 minutes and dried in an 80°C oven for 12 hours. The negative electrode material layer was scraped off the negative electrode current collector and analyzed by ICP-OES.

[0166] Functional group type test:

[0167] The positive electrode, negative electrode and separator were tested by Fourier transform infrared reflectance spectrometer (ATR-FTIR) with the wave number range set to 4000 cm -1 Up to 400cm -1 , and confirm the type of functional group according to the standard card.

[0168] Adhesion test:

[0169] After discharging the lithium-ion battery at 0.5C to 3.0V, the battery was disassembled to obtain a sample consisting of a positive electrode sheet, a negative electrode sheet, and a separator. The sample was cut into a 100mm×20mm strip. One side of the positive electrode sheet was attached to the double-sided tape. A roller was rolled back and forth on the strip four times. One end of the strip was clamped in the tensile testing machine fixture and stretched 180°. The tensile testing machine was turned on and the positive electrode sheet was pulled at a constant speed of 50mm / min until it separated from the separator surface. The peel force F2 between the positive electrode sheet and the separator was obtained. The negative side of the strip was attached to the double-sided tape to measure the peel force F1 between the negative electrode sheet and the separator.

[0170] Porosity test:

[0171] Porosity = (apparent volume of sample - true volume of sample) / apparent volume of sample.

[0172] Apparent volume of the sample: Use a solid mold (5 cm × 10 cm) with an area of S1 to punch out and measure the thickness h of the sample to obtain the apparent volume V of the sample S =S1×h; where the sample is a diaphragm.

[0173] True volume of the sample: The test principle uses the Archimedean principle of gas displacement through the gas displacement method, utilizing Bohr's law (PV = nRT) for inert gases with small molecular diameters under certain conditions to accurately measure the true volume of the sample being tested. Place the punched sample in the true density tester, seal the test system, and introduce helium according to the procedure. By measuring the gas pressure in the sample chamber and expansion chamber, the true volume is calculated according to Bohr's law:

[0174] (1)P1(V cell -V samp )=n c RT a ;

[0175] (2)P a V exp =n e RT a ;

[0176] When the valve is opened, the pressure drops to the intermediate value P2, and the mass conservation law becomes: (3) P2 (V cell -V samp +V exp )=n c RT a +n e RT a ;

[0177] Then the actual volume of the sample is: (4)V samp =(V cell -V exp )×(P2-P a ) / (P1-P2);

[0178] Among them, n c is the molar mass of the gas in the sample cup; n e is the molar mass of the gas in the expanding gas; R is the ideal gas constant; T a is the ambient temperature; V cell is the volume of the sample cup, V samp is the true volume of the sample; V exp is the volume of the expansion chamber; P1 is the gas pressure in the sample chamber, P2 is the equilibrium pressure after the gas diffuses in the entire system, and P a is the pressure of the gas in the expansion chamber.

[0179] The membrane was immersed in dimethyl carbonate for 1 minute and then its apparent volume and true volume were measured to calculate the porosity P1. The membrane was immersed in dimethyl carbonate for 15 minutes and then its apparent volume and true volume were measured to calculate the porosity P2.

[0180] Gas chromatography-mass spectrometry detection (GC-MSD) test:

[0181] The positive electrode sheet, negative electrode sheet, and separator obtained during the sampling process were soaked in acetonitrile for 15 minutes, and the soaked liquid was filtered through a microporous membrane to remove particulate matter, thereby obtaining a solution containing the first oligomer, a solution containing the second oligomer, and a solution containing the third oligomer, respectively. The samples were then analyzed using a GC-MSD Agilent-6890N-5973N analyzer. If the mass spectra of the solution containing the first oligomer, the solution containing the second oligomer, and the solution containing the third oligomer all exhibit characteristic peaks within the same retention time period and at approximately the same peak positions, it indicates that the first oligomer, the second oligomer, and the third oligomer have the same repeating unit; otherwise, the same repeating unit does not exist.

[0182] Electrolyte Sampling: Discharge the lithium-ion battery three times at 25°C at a constant current of 0.5C to 3V. Remove the packaging bag and collect the gelled material from the lithium-ion battery. Add it to acetonitrile and mix thoroughly. Centrifuge the mixture and collect the supernatant as the electrolyte test sample.

[0183] The types and contents of fluorinated organic compounds in the electrolyte test samples were tested using a GC-MSD Agilent-6890N-5973N analyzer, wherein the types of fluorinated compounds were determined by comparing with standard cards.

[0184] Cyclic performance test:

[0185] The cycle was charged at a constant current of 4C to 4.53V, then charged at a constant voltage of 4.53V to a current less than or equal to 0.05C, and then discharged at a constant current of 0.5C to 3.0V. The discharge capacity and thickness of the third cycle were used as the benchmark values. The discharge capacity and thickness after 600 cycles were tested, and the cycle capacity retention rate and volume expansion rate were calculated.

[0186] Cycle capacity retention rate=discharge capacity at the 3rd cycle / discharge capacity at the 600th cycle×100%.

[0187] Volume expansion ratio=thickness at the 600th cycle / thickness at the 3rd cycle×100%.

[0188] Interface testing:

[0189] A high-resolution camera was used to photograph the surface of the negative electrode to determine the state of lithium deposition on the negative electrode. Image processing software (ImageJ) was then used to calculate and analyze the lithium deposition area of the negative electrode. The lithium deposition interface ratio (S) = lithium deposition area / total area of the negative electrode × 100%. S ≤ 10% indicates mild lithium deposition; 10% < S ≤ 20% indicates moderate lithium deposition; and 20% < S indicates severe lithium deposition. The lithium deposition area refers to the total area of lithium deposition on both surfaces of the negative electrode along its thickness, and the total area of the negative electrode refers to the sum of the areas of both surfaces along its thickness.

[0190] Example 1-1

[0191] <Preparation of positive electrode sheet>

[0192] The positive electrode active material LiCoO2, the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride were mixed in a mass ratio of 94.8:2.8:2.4. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry was obtained. The positive electrode slurry was evenly coated on one surface of a 10μm thick positive electrode current collector aluminum foil and dried at 120°C to obtain a positive electrode sheet coated on one side with a positive electrode material layer of 80μm. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode material layer. After drying at 120°C, the sheet was cold pressed, cut into pieces, and the tabs were welded to obtain a positive electrode sheet with a size of 74mm×867mm for future use. The thickness of the positive electrode material layer on one side was 76μm.

[0193] <Preparation of negative electrode sheet>

[0194] The negative electrode active material, SiC, and artificial graphite, along with the binder polyvinylidene fluoride and the conductive agent Super P, were mixed in a mass ratio of 90:3:3.5:3.5. Deionized water was added as a solvent to create a slurry with a solid content of 45 wt%. The mixture was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The SiC had a silicon to carbon mass ratio of 1:1, and the binder was a 1:1 mixture of styrene-butadiene rubber and carboxymethyl cellulose. The negative electrode slurry was evenly coated on one surface of a 6μm-thick copper foil for the negative electrode current collector and dried at 120°C to obtain a negative electrode sheet coated on one side with a negative electrode material layer of 80μm thickness. The above steps were repeated on the other side of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode material layer. After drying at 120°C, the sheet was cold pressed, cut, and then welded to the tabs to obtain a negative electrode sheet measuring 78mm x 875mm for future use. The negative electrode material layer on one side was 64μm thick.

[0195] <Preparation of Electrolyte>

[0196] In an environment with a water content of less than 10 ppm, ethylene carbonate, diethyl carbonate, propylene carbonate, and vinylene carbonate are mixed in a mass ratio of 40:30:28:2 to obtain an organic solvent. Then, an electrolyte salt LiPF6, a monomer, and an initiator are added to the organic solvent and mixed evenly to obtain an electrolyte. The electrolyte salt comprises 12.5% by mass, the monomer comprises W4 by mass, and the remainder comprises organic solvent, based on the mass of the electrolyte. The first monomer is n-butyl methacrylate, and the mass percentage of the first monomer, W41, is 50%; the second monomer is triethylene glycol diacrylate, and the mass percentage of the second monomer, W42, is 50%; the initiator comprises 5% by mass, based on the mass of the monomers, and the initiator is azobisisobutyronitrile. The mass of the electrolyte is the mass of all substances excluding the initiator.

[0197] <Diaphragm>

[0198] A porous polyethylene film (supplied by Celgard) with a thickness of 7 μm was used as the separator, and the porosity of the separator was 90%.

[0199] <Preparation of lithium-ion batteries>

[0200] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator positioned between the positive and negative electrodes to act as a separator, and then wound to form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, and then injected with the prepared electrolyte. The lithium-ion battery is produced through vacuum packaging, standing, formation, degassing, polymerization, and trimming. The upper formation voltage limit is 4.15V, the formation temperature is 70°C, and the formation standing time is 2 hours.

[0201] Example 1-2 Example 1-26

[0202] The preparation parameters were adjusted according to Table 1, and the rest were the same as those in Example 1-1. In Example 1-26, the mass ratio of SiC, artificial graphite, binder, and conductive agent was 10:83:3.5:3.5, and the rest were the same as those in Example 1-1.

[0203] Examples 1-27

[0204] Except for preparing the negative electrode slurry according to the following steps, the rest is the same as Example 1-1:

[0205] The negative electrode active material Si and artificial graphite, a binder, and a conductive agent Super P were mixed in a mass ratio of 80:5:10:5, and deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. The negative electrode slurry was obtained after being uniformly stirred with a vacuum mixer.

[0206] Example 2-1 to Example 2-11

[0207] The preparation process of the electrolyte was the same as Example 1-1 except that fluorine-containing organic matter was added according to Table 2, the mass percentage of the organic solvent was changed accordingly, and the mass percentage of the electrolyte salt remained unchanged.

[0208] Example 3-1 to Example 3-5

[0209] Except for adjusting the positive electrode slurry or the negative electrode slurry in the following manner, the rest is the same as Example 1-1:

[0210] During the preparation of the positive electrode slurry, the mass percentage of the positive electrode binder was adjusted according to Table 3, and the mass percentage of the positive electrode active material was changed accordingly, while the mass percentage of the conductive agent remained unchanged;

[0211] During the preparation of the negative electrode slurry, the mass percentage of the negative electrode binder was adjusted according to Table 3, and the mass percentage of the negative electrode active material changed accordingly, while the mass ratio of SiC and artificial graphite and the mass percentage of the conductive agent remained unchanged.

[0212] Comparative Example 1

[0213] Except that the monomer and initiator are not added during the electrolyte preparation process, the content of the organic solvent is changed accordingly, and the content of the electrolyte salt remains unchanged, the rest is the same as Example 1-1.

[0214] Comparative Example 2 to Comparative Example 3

[0215] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0216] The preparation parameters and performance tests of various embodiments and comparative examples are shown in Tables 1 to 3.

[0217]

[0218]

[0219]

[0220] It can be seen from Examples 1-1 to 1-27 and Comparative Examples 1 to 3 that when the first oligomer, the second oligomer and the third oligomer have the same repeating unit and the thermal decomposition temperature is independently between 90°C and 180°C, and Max(T C ,T A ,T S )-Min(T C ,T A ,T S) is within the scope of the present application, the obtained lithium ion battery has a higher cycle capacity retention rate, a lower cycle thickness expansion rate, and a lighter degree of lithium deposition. In Comparative Example 1, no monomer is added to the electrolyte, and there is no oligomer in the obtained positive electrode sheet, negative electrode sheet and separator. The lithium ion battery has a low cycle capacity retention rate, a high cycle thickness expansion rate and severe lithium deposition; in Comparative Example 2, Max (T C ,T A ,T S )-Min(T C ,T A ,T S ) is not within the scope of this application. Although the degree of lithium deposition is milder than that of Comparative Example 1, it is still more severe than that of the above-mentioned examples, and the cycle capacity retention rate is low and the cycle thickness expansion rate is high. The thermal decomposition temperatures of the first, second, and third oligomers in Comparative Example 3 are not within the scope of this application. Although the thickness expansion rate of the resulting lithium-ion battery is small, the cycle capacity retention rate is the lowest and the degree of lithium deposition is the most severe. This shows that the lithium-ion batteries in the examples of this application have improved interface problems and cycle performance compared to the lithium-ion batteries in the comparative examples.

[0221] Specifically, if Figure 1 As shown, in the DSC spectrum of the positive electrode material layer in Example 1-1, the temperature of the first thermal decomposition peak is T C is 155℃; Figure 2 As shown, in the DSC spectrum of the negative electrode material layer in Example 1-1, the temperature of the second thermal decomposition peak is T A is 152℃; Figure 3 As shown in the DSC spectrum of the diaphragm in Example 1-1, the temperature of the third thermal decomposition peak is T S It is 169℃. Figure 4 From top to bottom (a) to (c) are the GC-MSD spectra of the sample solutions corresponding to the positive electrode material layer, the negative electrode material layer and the separator in Example 1-1. It can be seen that the sample solutions corresponding to the positive electrode material layer, the negative electrode material layer and the separator have characteristic peaks at retention times of 1.62min to 1.70min and the peak positions are roughly the same, and there are characteristic peaks at retention times of 2.00min to 2.07min and the peak positions are roughly the same, indicating that the first oligomer in the positive electrode material layer, the second oligomer in the negative electrode material layer and the third oligomer in the separator have the same repeating unit. In addition, after testing, the first oligomer in the positive electrode material layer, the second oligomer in the negative electrode material layer and the third oligomer in the separator in Examples 1-1 to 1-27 also have the same repeating unit. Thus, the first oligomer, the second oligomer and the third oligomer also have the same functional group, and the specific types of functional groups are shown in Table 1.

[0222] The peel force F1 between the negative electrode and separator, and the peel force F2, P1, and P2 between the positive electrode and separator vary with the weight percentage of the monomers, and P2 / P1 also changes accordingly, which in turn affects the interface and cycle performance of the lithium-ion battery. As can be seen from Examples 1-1 to 1-8, Comparative Examples 2 and 3, when the weight percentage of the monomers is within the range of this application, F1, F2, and P2 / P1 are also within the range of this application, the resulting lithium-ion battery has a higher cycle capacity retention rate, a lower cycle thickness expansion rate, and a lower degree of lithium plating, which means that the interface problems and cycle performance of the lithium-ion battery are improved.

[0223] The type and mass percentage of the first monomer and the second monomer will affect T C 、T A 、T S , which in turn affects the interface and cycle performance of the lithium-ion battery. It can be seen from Examples 1-1 and 1-9 to 1-26 that when the types and mass percentages of the first monomer and the second monomer are within the scope of the present application, the obtained lithium-ion battery has a higher cycle capacity retention rate, a lower cycle thickness expansion rate, and a lighter degree of lithium plating, that is, the lithium-ion battery has less interface problems and has good cycle performance.

[0224] It can be seen from Examples 1-1 to 1-27 that the weight loss rate m of the negative electrode material layer between 90°C and 180°C varies with the mass percentage of the monomer, the type and mass percentage of the first monomer and the second monomer, and 100m / W1 and m / H×100 also change accordingly. When 100m / W1 and m / H×100 are within the scope of this application, the obtained lithium-ion battery has a higher cycle capacity retention rate, a lower cycle thickness expansion rate, and a lighter degree of lithium plating, that is, the lithium-ion battery has smaller interface problems and has good cycle performance.

[0225] Table 2

[0226]

[0227] Note: “ / ” in Table 2 indicates that there is no corresponding parameter.

[0228] It can be seen from Examples 1-1 and 2-1 to 2-11 that the introduction of fluorine-containing organic matter into the electrolyte can further increase the peeling force F1 between the negative electrode sheet and the diaphragm, and the peeling force F2 between the positive electrode sheet and the diaphragm, thereby improving the large thickness expansion rate of lithium ions. At the same time, the lithium-ion battery has a higher cycle capacity retention rate and a lighter degree of lithium plating, that is, the lithium-ion battery has less interface problems and has good cycle performance.

[0229] The content and type of fluorinated organic matter can affect the peel force F1 between the negative electrode and the separator, and the peel force F2 between the positive electrode and the separator, thereby affecting the interface and cycle performance of the lithium-ion battery. As can be seen from Examples 2-1 to 2-11, when the content and type of fluorinated organic matter are within the range of this application, the peel force F1 between the negative electrode and the separator, and the peel force F2 between the positive electrode and the separator are also within the range of this application, the resulting lithium-ion battery has a high cycle capacity retention rate, a low cycle thickness expansion rate, and a low degree of lithium plating. In other words, the lithium-ion battery has fewer interface issues and has good cycle performance.

[0230] Table 3

[0231]

[0232] The content of the negative electrode binder affects the peel force F1 between the negative electrode sheet and the separator, and the content of the positive electrode binder affects the peel force F2 between the positive electrode sheet and the separator, thereby affecting the interface and cycle performance of the lithium-ion battery. From Examples 1-1, 3-1, and 3-5, it can be seen that when the mass percentages of the negative electrode binder and the positive electrode binder are within the range of this application, the peel force F1 between the negative electrode sheet and the separator, and the peel force F2 between the positive electrode sheet and the separator are also within the range of this application, the resulting lithium-ion battery has a high cycle capacity retention rate, a low cycle thickness expansion rate, and a low degree of lithium plating. In other words, the lithium-ion battery has fewer interface problems and has good cycle performance.

[0233] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0234] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive electrode material layer, the negative electrode sheet comprises a negative electrode material layer; the positive electrode material layer comprises a first oligomer, the negative electrode material layer comprises a second oligomer, and the separator comprises a third oligomer, wherein the first oligomer, the second oligomer, and the third oligomer have the same repeating unit and each independently has a thermal decomposition temperature between 90° C. and 180° C.; In the differential scanning calorimetry test spectrum of the positive electrode material layer, there is a first thermal decomposition peak between 90°C and 180°C, and the temperature of the first thermal decomposition peak is T C ; In the differential scanning calorimetry test spectrum of the negative electrode material layer, a second thermal decomposition peak exists between 90° C. and 180° C., and the temperature of the second thermal decomposition peak is T A ; In the differential scanning calorimetry test spectrum of the diaphragm, there is a third thermal decomposition peak between 90°C and 180°C, and the temperature of the third thermal decomposition peak is T S ; 0℃≤Max(T C ,T A ,T S )-Min(T C ,T A ,T S )≤20℃。 2. The secondary battery according to claim 1, wherein 8℃≤Max(T C ,T A ,T S )-Min(T C ,T A ,T S )≤17℃。 3. The secondary battery according to claim 1, wherein The peeling force F1 between the negative electrode plate and the separator is 15 N / m to 50 N / m, and the peeling force F2 between the positive electrode plate and the separator is 11 N / m to 45 N / m.

4. The secondary battery according to claim 1, wherein The porosity of the diaphragm after being immersed in dimethyl carbonate for 1 minute is P1, and the porosity of the diaphragm after being immersed in dimethyl carbonate for 15 minutes is P2, and 1≤P2 / P1≤1.

55.

5. The secondary battery according to claim 4, wherein 1≤P2 / P1≤1.

25.

6. The secondary battery according to any one of claims 1 to 5, wherein The positive electrode plate, the negative electrode plate and the separator include fluorine-containing organic matter, and the fluorine-containing organic matter includes at least one of fluorinated carbonates, fluorinated carboxylates, fluorinated linear ethers, fluorinated cyclic ethers, fluorinated sulfone compounds, fluorinated phosphides or fluorinated carbamates.

7. The secondary battery according to any one of claims 1 to 5, wherein The negative electrode material layer includes silicon material; Based on the mass of the negative electrode material layer, the mass percentage of silicon element is W1; in a thermogravimetric analysis test of the negative electrode material layer, the weight loss rate of the negative electrode material layer between 90° C. and 180° C. is m; 0.01≤100m / W1≤0.

11.

8. The secondary battery according to any one of claims 1 to 5, wherein The negative electrode plate includes a negative electrode material layer, and the thickness of the negative electrode material layer is H μm; In a thermogravimetric analysis test of the negative electrode material layer, the weight loss rate of the negative electrode material layer between 90° C. and 180° C. is m; 0.6≤m / H×100≤6.

3.

9. The secondary battery according to any one of claims 1 to 5, which satisfies at least one of the following characteristics: (1) The positive electrode material layer includes a positive electrode binder. Based on the mass of the positive electrode material layer, the mass percentage of the positive electrode binder is W2, 0.5%≤W2≤3.0%; (2) The negative electrode material layer includes a negative electrode binder. Based on the mass of the negative electrode material layer, the mass percentage of the negative electrode binder is W3, and 2%≤W3≤10%.

10. The secondary battery according to any one of claims 1 to 5, wherein the first oligomer, the second oligomer and the third oligomer independently include at least one of the following functional groups: -COO-, -O-CO-O-, -SO2O-, -PO4, -COOH, -SO2-, -SO-, -CONH2-, -CN, -O- or -OBO-.

11. A method for preparing a secondary battery according to any one of claims 1 to 10, comprising the following steps: (1) obtaining an electrolyte solution, wherein the electrolyte solution comprises a monomer, a solvent, and an electrolyte salt, wherein the mass percentage W4 of the monomer is 2% to 80% based on the mass of the electrolyte solution; Wherein, the monomer includes a first monomer and a second monomer, based on the total mass of the monomers, the mass percentage content W41 of the first monomer is 1% to 99%, and the mass percentage content W42 of the second monomer is 1% to 99%; the first monomer includes at least one of an acrylate monomer, a carbonate monomer, a sulfate monomer, a sulfonate monomer, a phosphate monomer, a carboxylate monomer, a sulfone monomer, an amide monomer, a nitrile monomer or an ether monomer; the second monomer includes at least one of an acrylate monomer, an amide monomer or a borate monomer; (2) injecting the electrolyte into a shell provided with an electrode assembly to initiate polymerization of the monomers, and obtaining the secondary battery after the polymerization is completed; wherein the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator.

12. The preparation method according to claim 11, wherein The electrolyte also includes a fluorinated organic compound, which includes at least one of a fluorinated carbonate, a fluorinated carboxylate, a fluorinated linear ether, a fluorinated cyclic ether, a fluorinated sulfone compound, a fluorinated phosphide or a fluorinated carbamate; based on the mass of the electrolyte, the mass percentage W5 of the fluorinated organic compound is 1% to 30%.

13. The preparation method according to claim 11 or 12, which satisfies at least one of the following characteristics: (1) The fluorocarbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, monofluoropropylene carbonate, trifluoropropylene carbonate, 4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]-dioxane-2-one, 4-(2,3,3,3-tetrafluoro-2-trifluoromethylpropyl)-[1,3]dioxane-2-one, 2,2,2-trifluoroethyl methyl carbonate, 2,2-difluoroethyl ethyl carbonate, ethyl (2,2,2-trifluoroethyl) carbonate, ethyl (1-fluoroethyl) carbonate or 2,2,2-trifluoroethyl (1-fluoroethyl) carbonate; The fluorocarboxylic acid ester includes at least one of α-fluoroγ-butyrolactone, β-fluoroγ-butyrolactone, methyl trifluoroacetate, ethyl trifluoroacetate, 2-fluoroethyl acetate, ethyl fluoroacetate, 2,2,2-trifluoroacetic acid methyl ester, 2,2-difluoroacetic acid methyl ester, 2,2,2-trifluoroacetic acid ethyl ester, 2,2,2-trifluoroacetic acid propyl ester, 2,2,2-trifluoroacetic acid butyl ester or 2,2,2-trifluoroacetic acid hexyl ester; The fluorinated linear ether includes at least one of fluoro-1,2-diethoxyethane, difluoro-1-ethoxy-2-methoxyethane, trifluoro-1-ethoxy-2-methoxyethane, fluoro-1,2-diethoxyethane, difluoro-1,2-diethoxyethane, trifluoro-1,2-diethoxyethane, tetrafluoro-1,2-diethoxyethane, tetrafluoro-1,2-diethoxyethane, pentafluoro-1,2-diethoxyethane or hexafluoro-1,2-diethoxyethane; The fluorinated cyclic ether includes at least one of 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane or 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane; The fluorinated sulfone compound includes at least one of 3,3,3-trifluoropropyl methyl sulfone, 3-fluoro-1,3-propane sultone, 2-fluorotetrahydrothiophene-1,1-dioxide, 3-fluorotetrahydrothiophene-1,1-dioxide, trifluoromethyl isopropyl sulfone or trifluoromethyl propyl methyl sulfone; The fluorinated phosphide includes at least one of tris(2,2,2-trifluoroethyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane-2-oxide, 2-(2,2,3,3,3-pentafluoropropoxy)-1,3,2-dioxaphospholane or 2-(2,2,3,3,3-pentafluoropropoxy)-4-(trifluoromethyl)-1,3,2-dioxaphospholane; The fluorocarbamate includes at least one of 2,2,2-trifluoroethyl-N,N-dimethylcarbamate, 1,1,1,3,3,3-hexafluoropropyl-N,N-dimethylcarbamate, 2,2,2-trifluoroethyl-N,N-diethylcarbamate or 1,1,1,3,3,3-hexafluoropropyl-N,N-diethylcarbamate; (2) the carbonate monomer comprises at least one of vinyl ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate or chloroethylene carbonate; The sulfate monomer includes at least one of vinyl sulfite, vinyl sulfite, 4-methyl vinyl sulfate or 4-ethyl vinyl sulfate; The sulfonate monomer includes at least one of 1,3-propylene sultone, 1,4-butane sulfonate or methylenedisulfonate; The phosphate monomer includes at least one of dimethyl vinyl phosphate, triethyl vinyl phosphate, diethyl propenyl phosphate, triethyl butenyl phosphate, diethyl (I)-buten-2-yl phosphonate, diethyl ethynyl phosphate, vinyl trifluoromethyl phosphate, vinyl-1-trifluoroethyl phosphate, diethyl fluorovinyl phosphate or 1-trifluoropropenylethyl phosphate; The carboxylate monomer includes vinyl acetate; The sulfone monomer includes at least one of methyl vinyl sulfone, ethyl vinyl sulfone, sulfolene, sulfolane or ethylene sulfoxide; The amide monomer includes acrylamide; The nitrile monomer includes at least one of acrylonitrile, succinonitrile, glutaronitrile or adiponitrile; The ether monomer includes at least one of 1,3-dioxolane, ethylene oxide, 1,2-propylene oxide, 4-methyl-1,3-dioxolane tetrahydrofuran, 2-methyltetrahydrofuran, 14-dioxane, ethylene glycol dimethyl ether, ethylene glycol diglycidyl ether or triethylene glycol divinyl ether; The acrylic ester monomers include acrylic acid, methacrylic acid, methyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, butyl acrylate, isodecyl acrylate, isooctyl acrylate, lauryl acrylate, isobornyl acrylate, isobornyl methacrylate, ethoxyethoxyethyl acrylate, cyanoacrylate, caprolactone acrylate, 2-phenoxyethyl acrylate, tetrahydrofuran acrylate, ethyl tetrahydrofuran acrylate, cyclotrimethylolpropane acrylate, 2-carboxyethyl acrylate, cyclohexyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, triethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dioctanoate, tetraethylene glycol dimethacrylate, 1,4-butanediol At least one of diol diacrylate, 1-4-butanediol dimethacrylate, 1,3-butanediol triacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, tripropylene glycol diacrylate, dipropylene glycol dimethacrylate, tripropylene glycol diacrylate, tripropylene glycol dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, 2(propoxylated)neopentyl glycol diacrylate, methoxypolyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, methoxypolyethylene glycol methacrylate, pentaerythritol triacrylate, propoxylated glycerol triacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, di(trimethylolpropane) tetraacrylate, or pentaerythritol tetraacrylate; The borate ester monomer includes at least one of phenyl borate, methyl borate, ethyl borate, benzyl borate or 4-fluorophenyl borate.

14. The preparation method according to claim 11 or 12, which satisfies at least one of the following characteristics: (1)3％≤W4≤50％； (2)2％≤W5≤20％； (3) the fluorocarbonate comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, trifluoropropylene carbonate, 2,2,2-trifluoroethyl methyl carbonate, 2,2-difluoroethyl ethyl carbonate, or ethyl (2,2,2-trifluoroethyl) carbonate; The fluorocarboxylate comprises at least one of α-fluoroγ-butyrolactone, methyl trifluoroacetate, ethyl trifluoroacetate, ethyl 2-fluoroacetate, methyl 2,2,2-trifluoroacetate or methyl 2,2-difluoroacetate; The fluorinated linear ether includes at least one of fluorinated 1,2-diethoxyethane, difluoro 1-ethoxy-2-methoxyethane, trifluoro 1-ethoxy-2-methoxyethane or tetrafluoro 1,2-diethoxyethane; The fluorinated cyclic ether includes at least one of 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane or 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane; The fluorinated sulfone compound includes at least one of 3,3,3-trifluoropropyl methyl sulfone or trifluoromethyl isopropyl sulfone; The fluorinated phosphide includes at least one of tris(2,2,2-trifluoroethyl)phosphate or tris(2,2,2-trifluoroethyl)phosphate; The fluorocarbamate includes at least one of 2,2,2-trifluoroethyl-N,N-dimethylcarbamate, 1,1,1,3,3,3-hexafluoropropyl-N,N-dimethylcarbamate or 2,2,2-trifluoroethyl-N,N-diethylcarbamate; (4) the carbonate monomer comprises at least one of vinyl ethylene carbonate and propylene carbonate; The sulfate monomer includes at least one of vinyl sulfite or vinyl sulfite; The sulfonate monomer includes at least one of 1,3-propylene sultone or 1,4-butane sulfonate; The phosphate monomer includes at least one of dimethyl vinyl phosphate, triethyl vinyl phosphate, diethyl propylene phosphate, vinyl-1-trifluoroethyl phosphate or diethyl fluorovinyl phosphate; The carboxylate monomer includes vinyl acetate; The sulfone monomer includes at least one of methyl vinyl sulfone, cyclopentane sulfone or cyclohexane sulfoxide; The amide monomer includes acrylamide; The nitrile monomer includes at least one of acrylonitrile, succinonitrile, glutaronitrile or adiponitrile; The ether monomer includes at least one of 1,3-dioxolane, ethylene oxide or 1,2-propylene oxide; The acrylic acid ester monomers include at least one of methyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1-4-butanediol dimethacrylate, 1,3-butanediol triacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, propoxylated glycerol triacrylate, di(trimethylolpropane) tetraacrylate or pentaerythritol tetraacrylate; The borate ester monomer includes at least one of methyl borate or ethyl borate. 15 . An electronic device comprising the secondary battery according to claim 1 or the secondary battery prepared by the preparation method according to claim 11 .

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