Composite pole piece as well as preparation method and application thereof

Abstract

The invention relates to a composite pole piece and a preparation method and application thereof. The preparation method of the composite pole piece comprises the following steps: coating at least one side surface of a current collector with slurry containing an ionic liquid, a polymer, an active material and a conductive agent to prepare an active layer; the polymer contains a vinylidene fluoride chain segment, and the ionic liquid comprises one or more of imidazolyl bis (trifluoromethylsulfonyl) imide and pyrrolidinium bis (fluorosulfonyl) imide; in the slurry, the mass ratio of the ionic liquid to the polymer is 3: (1-4). The composite pole piece prepared by the preparation method can form an interface with good stability with a solid electrolyte.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, and in particular to composite electrodes, their preparation methods, and their applications. Background Technology

[0002] In recent years, solid-state batteries, as a new generation of energy storage technology, have attracted much attention due to their advantages such as high safety and high energy density. Compared with traditional lithium-ion batteries, solid-state batteries significantly improve battery safety by using a solid electrolyte instead of a flammable and explosive liquid electrolyte.

[0003] However, solid-state battery technology still faces many challenges. Since the contact between the electrode and the electrolyte is mainly solid-solid, the physical contact is often not tight enough and the structural stability is poor, resulting in high impedance at the interface that seriously hinders ion transport. At the same time, poor local contact can also cause uneven current distribution, promote lithium dendrite growth and accelerate interfacial side reactions. All these problems result in poor electrochemical performance and cycle stability of the battery, especially at high temperatures, where the battery performance will decline significantly and cannot meet application requirements. Summary of the Invention

[0004] Therefore, it is necessary to provide a composite electrode that can make close contact with the solid electrolyte interface and still have excellent structural stability even at high temperatures, as well as its preparation method and application.

[0005] In a first aspect, this application provides a method for preparing a composite electrode.

[0006] A method for preparing a composite electrode includes the following steps:

[0007] An active layer is prepared by coating at least one side of a current collector with a slurry containing ionic liquid, polymer, active material, and conductive agent.

[0008] The polymer contains vinylidene fluoride segments, and the ionic liquid includes one or more of imidazole bis(trifluoromethylsulfonyl)imide and pyrrolidine-onium bis(fluorosulfonyl)imide;

[0009] In the slurry, the mass ratio of the ionic liquid to the polymer is 3:(1~4).

[0010] In some embodiments, the ionic liquid comprises one or more of 1-ethyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide, 1-methyl-1-propylpyrrolidineonium bis(fluorosulfonyl)imide, 1-ethyl-1-methylpyrrolidineonium bis(fluorosulfonyl)imide, 1-propyl-1-methylpyrrolidineonium bis(fluorosulfonyl)imide, and 1-butyl-1-methylpyrrolidineonium bis(fluorosulfonyl)imide; and / or

[0011] The polymer includes one or more of polyvinylidene fluoride homopolymer and polyvinylidene fluoride-hexafluoropropylene copolymer, wherein the molecular weight of the first polymer is 400,000 to 600,000.

[0012] In some embodiments, the composite electrode is a composite positive electrode, and the thickness of the active layer of the composite positive electrode is 10 μm to 70 μm.

[0013] In some embodiments, the active material of the composite positive electrode includes one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium nickel oxide, and lithium cobalt oxide; and / or

[0014] The carbon nanotubes have an average tube length of 5μm to 10μm and an average tube diameter of 7μm to 15μm.

[0015] And / or, the mass ratio of the active material to the conductive agent is 90:10 to 99.5:0.5.

[0016] In some embodiments, the composite electrode is a composite negative electrode; the thickness of the active layer of the composite negative electrode is 10μm~60μm.

[0017] In some embodiments, the active material of the composite negative electrode includes one or more of graphite, lithium titanate, and hard carbon; and / or

[0018] The conductive agent in the composite negative electrode sheet includes conductive carbon black, wherein the resistivity of the conductive carbon black powder is ≤0.25Ω·cm; and / or

[0019] The mass ratio of the active material to the conductive agent is 95:5 to 99.5:0.5.

[0020] In a second aspect, this application provides a battery.

[0021] It includes a positive electrode, a negative electrode, and an electrolyte membrane, wherein the electrolyte membrane is disposed between the positive electrode and the negative electrode; the positive electrode includes a composite electrode sheet prepared by the above-described preparation method; and / or, the negative electrode includes a composite electrode sheet prepared by the above-described preparation method.

[0022] In some embodiments, the electrolyte membrane comprises a gel-solid electrolyte membrane.

[0023] In some embodiments, the gel solid electrolyte membrane includes a diaphragm impregnated with an electrolyte composite liquid, the electrolyte composite liquid including a second ionic liquid and a lithium salt; the second ionic liquid includes one or more of pyrrolidineonium-based ionic liquids and imidazolium-based ionic liquids.

[0024] A third aspect of this application provides an electrical device, including the battery described above.

[0025] Research has shown that by modifying polyvinylidene fluoride (PVDF) with ionic liquids containing imidazole-based bis(fluorosulfonyl)imide or pyrrolidine-onium-based bis(fluorosulfonyl)imide in specific proportions, the γ-phase (T3GT3G') of PVDF segments can be effectively transformed into a highly polar β-phase (TTT), thereby significantly improving the ionic conductivity of PVDF segments. Based on this, mixing the modified polymer with electrode materials and using it to prepare the electrode active layer can effectively improve the mechanical properties of the electrode sheet, as well as the interfacial contact performance and structural stability with conventional solid electrolytes, while maintaining good electrical performance. This, in turn, significantly improves the electrochemical performance and cycle capacity retention of the resulting battery. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The images show the XRD patterns of the polyvinylidene fluoride-hexafluoropropylene copolymer of Example 1.1 of this application and the polyvinylidene fluoride-hexafluoropropylene copolymer modified with ionic liquid. Detailed Implementation

[0028] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0029] In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. In this application, "at least one" means one or more, such as one, two, or more than two. "Multiple" or "several" means at least two, such as two, three, etc.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0032] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0033] In this application, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0034] Unless otherwise specified, the average molecular weight of polymers used in this application refers to weight-average molecular weight.

[0035] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0036] The first aspect of this application provides a composite positive electrode sheet with better contact performance with electrolyte and more stable performance at high temperatures.

[0037] For example, an active layer is prepared by coating a slurry containing an ionic liquid, a polymer, an active material, and a conductive agent onto at least one surface of a current collector;

[0038] The polymer contains vinylidene fluoride segments, and the ionic liquid includes one or more of imidazole bis(trifluoromethylsulfonyl)imide and pyrrolidine-onyl bis(fluorosulfonyl)imide.

[0039] In the slurry, the mass ratio of ionic liquid to polymer is 3:(1~4).

[0040] Research has shown that by modifying polyvinylidene fluoride (PVDF) with ionic liquids containing imidazole-based bis(fluorosulfonyl)imide or pyrrolidine-onium-based bis(fluorosulfonyl)imide in specific proportions, the γ-phase (T3GT3G') of PVDF segments can be effectively transformed into a highly polar β-phase (TTT), thereby significantly improving the ionic conductivity of PVDF segments. Based on this, mixing the modified polymer with electrode materials and using it to prepare the electrode active layer can effectively improve the mechanical properties of the electrode sheet, as well as the interfacial contact performance and structural stability with conventional solid electrolytes, while maintaining good electrical performance. This, in turn, significantly improves the electrochemical performance and cycle capacity retention of the resulting battery.

[0041] In this embodiment, the mass ratio of ionic liquid to polymer can be, but is not limited to, 3:1, 3:2, 1:1, 3:4, or other values ​​within the range of 3:(1~4). Maintaining the above-mentioned addition range can improve the ionic conductivity of the first polymer while avoiding excessive residual ionic liquid, thus preventing significant hindrance to lithium-ion migration. The polymer helps improve the mechanical properties and structural stability of the electrode material, and helps the electrode sheet maintain good stability at high temperatures. Simultaneously, the polymer and electrolyte membrane have superior interfacial compatibility, effectively improving the interfacial performance between the electrode sheet and the electrolyte membrane. Furthermore, thanks to the excellent mechanical and film-forming properties of polyvinylidene fluoride (PVDF), it can effectively mitigate the hindrance of ionic liquid to lithium-ion migration.

[0042] In some embodiments, the ionic liquid includes one or more of 1-ethyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide, 1-methyl-1-propylpyrrolidineonium bis(fluorosulfonyl)imide, 1-ethyl-1-methylpyrrolidineonium bis(fluorosulfonyl)imide, 1-propyl-1-methylpyrrolidineonium bis(fluorosulfonyl)imide, and 1-butyl-1-methylpyrrolidineonium bis(fluorosulfonyl)imide. Using the above-mentioned ionic liquids can effectively induce phase transitions in the polyvinylidene fluoride (PVDF) segments, thereby effectively improving the ionic conductivity of the polymer.

[0043] Furthermore, the ionic liquid is one or more of 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide and 1-butyl-1-methylpyrrolidineonium bis(fluorosulfonyl)imide. Studies have found that using the above-mentioned ionic liquid can effectively induce a phase transition in the polyvinylidene fluoride (PVDF) chain segments, thereby effectively improving the piezoelectric, thermoelectric, ferroelectric properties, and ionic conductivity of the PVDF chain segments.

[0044] In some embodiments, the polymer includes one or more of polyvinylidene fluoride homopolymer and polyvinylidene fluoride-hexafluoropropylene copolymer. The first polymer helps improve the mechanical properties and structural stability of the electrode material, and helps the electrode sheet maintain good stability at high temperatures. Simultaneously, the first polymer and the electrolyte membrane have superior interfacial compatibility, which can effectively improve the interfacial performance between the electrode sheet and the electrolyte membrane.

[0045] In some embodiments, the molecular weight of the polymer is 400,000 to 600,000. Optionally, the average molecular weight of the first polymer can be, but is not limited to, 400,000, 500,000, 600,000, or other values ​​in the range of 400,000 to 600,000.

[0046] In some embodiments, the slurry further includes a solvent, which includes one or more of N,N-dimethylformamide, tetrahydrofuran, dimethylacetamide, tetramethylurea, dimethyl sulfoxide, N-methylpyrrolidone, acetone, cyclohexanone, n-butyl acetate, methyl isobutyl ketone, and ethylene glycol diethyl ether.

[0047] In some embodiments, the ionic liquid, polymer, and solvent are mixed to form a composite solution. Optionally, the mixing rate is 500 r / min to 2000 r / min, and the mixing time is 4 h to 24 h.

[0048] A slurry is prepared by mixing the composite solution with an active material and a conductive agent. Optionally, the mixing rate is 500 r / min to 2000 r / min, and the mixing time is 4 h to 24 h.

[0049] In some embodiments, the active layer is prepared by vacuum drying. Optionally, the active layer is formed by vacuum drying at 80°C to 160°C for 8 to 24 hours.

[0050] In some embodiments, the composite electrode is a composite positive electrode, and the thickness of the active layer of the composite positive electrode is 10 μm to 70 μm. Optionally, the thickness of the active layer of the composite positive electrode can be, but is not limited to, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, or other values ​​within the range of 10 μm to 70 μm.

[0051] In some embodiments, the active material of the composite positive electrode includes one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium nickel oxide, and lithium cobalt oxide.

[0052] In some embodiments, the conductive agent of the composite positive electrode includes carbon nanotubes.

[0053] In some of these embodiments, the average length of the carbon nanotubes is 5 μm to 10 μm.

[0054] In some of these embodiments, the average diameter of the carbon nanotubes is 7 μm to 15 μm.

[0055] In some embodiments, the mass ratio of active material to conductive agent in the composite positive electrode is 90:10 to 99.5:0.5.

[0056] In some embodiments, the solid content of the slurry for the composite positive electrode is 40% to 80%. Optionally, the solid content of the slurry for the composite positive electrode can be, but is not limited to, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or other values ​​within the range of 40% to 80%. This helps to form a dense positive electrode active layer of appropriate thickness.

[0057] In some embodiments, the current collector of the composite positive electrode includes aluminum foil.

[0058] In some embodiments, the composite electrode is a composite negative electrode, and the thickness of the active layer of the composite negative electrode is 10 μm to 70 μm. Optionally, the thickness of the active layer of the composite negative electrode can be, but is not limited to, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, or other values ​​within the range of 10 μm to 70 μm.

[0059] In some embodiments, the active material of the composite negative electrode includes one or more of graphite, lithium titanate, and hard carbon.

[0060] In some embodiments, the conductive agent of the composite negative electrode sheet includes conductive carbon black.

[0061] In some embodiments, the resistivity of the conductive carbon black powder is ≤0.25Ω·cm.

[0062] In some embodiments, the mass ratio of active material to conductive agent in the composite negative electrode sheet is 95:5 to 99.5:0.5.

[0063] In some embodiments, the solid content of the slurry for the composite negative electrode is 40% to 80%. Optionally, the solid content of the slurry for the composite positive electrode can be, but is not limited to, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or other values ​​within the range of 40% to 80%. This helps to form a dense, appropriately thick negative electrode active layer.

[0064] In some embodiments, the current collector of the composite negative electrode sheet includes copper foil.

[0065] In a third aspect, this application provides a battery.

[0066] For example, the battery includes a positive electrode, a negative electrode, and an electrolyte membrane disposed between the positive electrode and the negative electrode; wherein the positive electrode includes a composite electrode sheet prepared by the above-described preparation method; and / or, the negative electrode includes a composite electrode sheet prepared by the above-described preparation method.

[0067] In some embodiments, the positive electrode is a composite positive electrode sheet, and the negative electrode is a composite negative electrode sheet.

[0068] In some of these implementations, the battery includes a solid-state battery or a solid-liquid battery.

[0069] In some embodiments, the electrolyte membrane includes a gel-solid electrolyte membrane.

[0070] In some embodiments, the gel solid electrolyte membrane includes a diaphragm impregnated with an electrolyte complex liquid comprising a second ionic liquid and a lithium salt.

[0071] In some embodiments, the amount of lithium salt added relative to the second ionic liquid in the electrolyte complex solution is 10 mg / ml to 200 mg / ml. Optionally, the amount of lithium salt added relative to the second ionic liquid can be, but is not limited to, 10 mg / ml, 20 mg / ml, 30 mg / ml, 40 mg / ml, 50 mg / ml, 70 mg / ml, 90 mg / ml, 110 mg / ml, 130 mg / ml, 150 mg / ml, 170 mg / ml, 200 mg / ml, or other values ​​within the range of 10 mg / ml to 200 mg / ml.

[0072] In some embodiments, the diaphragm includes one or more of PE diaphragms, PP diaphragms, PI diaphragms, aramid diaphragms, and cellulose diaphragms.

[0073] In some embodiments, the second ionic liquid includes one or more of pyrrolidineonium-based ionic liquids and imidazolium-based ionic liquids.

[0074] In some embodiments, the lithium salt includes one or more of LiPF6, LiClO4, LiAsF6, LiBF4, LiBOB, LiDFOB, LiTFSI, LiFSI, LiPO2F2, and LiTDI.

[0075] In a fourth aspect, this application provides an electrical device, including the battery described above. The electrical device can include mobile devices and electric vehicles. The mobile device can be a mobile phone, a laptop computer, etc.; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.

[0076] The present application will be further described in detail below with reference to specific embodiments.

[0077] Unless otherwise specified, the raw materials used in the following specific embodiments and comparative examples are all commercially available products; the instruments used are all commercially available products; and the processes used are all conventionally selected by those skilled in the art unless otherwise specified.

[0078] Example 1.1

[0079] This embodiment provides a composite positive electrode sheet.

[0080] The preparation method of the composite positive electrode is as follows:

[0081] 0.2 g of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 0.4 g of polyvinylidene fluoride-hexafluoropropylene copolymer were dissolved in N-methylpyrrolidone and stirred at 40 °C for 6 h to obtain a composite solution.

[0082] The composite solution was mixed with 0.5g of lithium iron phosphate and 0.005g of carbon nanotubes, stirred at 60°C for 6 hours, and the solid content was adjusted to 60% to obtain the slurry of the composite positive electrode sheet.

[0083] The slurry of the composite positive electrode sheet was coated onto aluminum foil and dried in a vacuum drying oven at 80°C for 18 hours to obtain a positive active layer with a thickness of 60 μm, thus forming the composite positive electrode sheet.

[0084] Example 1.2

[0085] This embodiment provides a composite positive electrode sheet.

[0086] The preparation method of the composite positive electrode is as follows:

[0087] 0.3 g of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 0.3 g of polyvinylidene fluoride-hexafluoropropylene copolymer were dissolved in N-methylpyrrolidone and stirred at 40 °C for 6 h to obtain a composite solution.

[0088] The composite solution was mixed with 0.5g of lithium iron phosphate and 0.005g of carbon nanotubes, stirred at 60℃ for 6h, and the solid content was adjusted to 60% to obtain the slurry of the composite positive electrode sheet.

[0089] The slurry of the composite positive electrode sheet was coated onto aluminum foil and dried in a vacuum drying oven at 80°C for 18 hours to obtain a positive active layer with a thickness of 60 μm, thus forming the composite positive electrode sheet.

[0090] Example 1.3

[0091] The preparation method of the composite positive electrode is as follows:

[0092] 0.2 g of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 0.4 g of polyvinylidene fluoride-hexafluoropropylene copolymer were dissolved in N-methylpyrrolidone and stirred at 40 °C for 6 h to obtain a composite solution.

[0093] The composite solution was mixed with 1g of lithium iron phosphate and 0.008g of carbon nanotubes, stirred at 60°C for 6 hours, and the solid content was adjusted to 60% to obtain the slurry of the composite positive electrode sheet.

[0094] The slurry of the composite positive electrode sheet was coated onto copper foil and dried in a vacuum drying oven at 80°C for 18 hours to obtain a positive active layer with a thickness of 60 μm, thus forming the composite positive electrode sheet.

[0095] Example 2.1

[0096] This embodiment provides a composite negative electrode sheet.

[0097] The preparation method of the composite negative electrode sheet is as follows:

[0098] 0.2 g of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 0.4 g of polyvinylidene fluoride-hexafluoropropylene copolymer were dissolved in N-methylpyrrolidone and stirred at 60 °C for 4 h to obtain a composite solution.

[0099] The composite solution was mixed with 0.3g of graphite and 0.003g of conductive carbon black, and stirred at 60℃ for 6 hours to adjust the solid content to 60%, thus obtaining the slurry of the composite positive electrode sheet.

[0100] The slurry of the composite negative electrode sheet is coated onto copper foil and dried in a vacuum drying oven at 100°C for 18 hours to obtain a negative electrode active layer with a thickness of 60 μm, thus forming the composite negative electrode sheet.

[0101] Comparative Example 1.1

[0102] This comparative example provides a composite positive electrode sheet.

[0103] The preparation method of the composite positive electrode is as follows:

[0104] 0.8 g of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 0.2 g of polyvinylidene fluoride-hexafluoropropylene copolymer were dissolved in N-methylpyrrolidone and stirred at 40 °C for 6 h to obtain a composite solution.

[0105] The composite solution was mixed with 0.5g of lithium iron phosphate and 0.005g of carbon nanotubes, stirred at 60°C for 6 hours, and the solid content was adjusted to 60% to obtain the slurry of the composite positive electrode sheet.

[0106] The slurry of the composite positive electrode sheet was coated onto aluminum foil and dried in a vacuum drying oven at 80°C for 18 hours to obtain a positive active layer with a thickness of 60 μm, thus forming the composite positive electrode sheet.

[0107] Comparative Example 1.2

[0108] This comparative example provides a composite positive electrode sheet.

[0109] The preparation method of the composite positive electrode is as follows:

[0110] 0.95g of lithium iron phosphate, 0.01g of carbon nanotubes, 0.04g of PVDF and 0.02g of lithium lanthanum zirconium oxide were added to N-methylpyrrolidone and stirred at 40℃ for 6h to obtain a slurry for the composite positive electrode.

[0111] The slurry of the composite positive electrode sheet is coated onto aluminum foil and dried in a vacuum drying oven at 80°C for 18 hours to obtain the positive active layer, thus forming the composite positive electrode sheet.

[0112] Comparative Example 2.1

[0113] This comparative example provides a composite negative electrode sheet.

[0114] The preparation method of the composite negative electrode sheet is as follows:

[0115] 0.8g graphite, 0.008g conductive carbon black, 0.04g PVDF and 0.015g lithium lanthanum zirconium oxide were added to N-methylpyrrolidone and stirred at 60℃ for 6h to obtain a slurry for the composite negative electrode sheet.

[0116] The slurry of the composite negative electrode sheet is coated onto copper foil and dried in a vacuum drying oven at 100°C for 18 hours to obtain the negative electrode active layer, thus forming the composite negative electrode sheet.

[0117] Test Example 1

[0118] The composite positive electrode sheet of Example 1.1 and the negative composite electrode sheet of Example 2.1 were used as the positive and negative electrodes of the battery, respectively, and the battery was assembled with a PP separator impregnated with an electrolyte composite solution (the amount of LiTFSI added relative to 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide was 0.05 g / ml).

[0119] Test Example 2

[0120] The difference from Test Example 1 is that the composite positive electrode sheet of Example 1.2 and the composite negative electrode sheet of Example 2.1 are used as the positive and negative electrodes of the battery.

[0121] Test Example 3

[0122] The difference from Test Example 1 is that the composite positive electrode sheet of Example 1.3 and the composite negative electrode sheet of Example 2.1 are used as the positive and negative electrodes of the battery.

[0123] Test Example 4

[0124] The difference from Test Example 1 is that the composite positive electrode of Comparative Example 1.1 and the composite negative electrode of Example 2.1 are used as the positive and negative electrodes of the battery.

[0125] Test Example 5

[0126] The difference from Test Example 1 is that the composite positive electrode of Comparative Example 1.2 and the composite negative electrode of Example 2.1 are used as the positive and negative electrodes of the battery.

[0127] Test Example 6

[0128] The difference from Test Example 1 is that the composite positive electrode sheet of Example 1.1 and the composite negative electrode sheet of Comparative Example 2.1 are used as the positive and negative electrodes of the battery.

[0129] Test Example 7

[0130] The difference from Test Example 1 is that the composite positive electrode of Comparative Example 1.2 and the composite negative electrode of Comparative Example 2.1 are used as the positive and negative electrodes of the battery.

[0131] Test methods

[0132] The batteries of each embodiment were subjected to 1C cycle testing at room temperature. The LFP charge / discharge voltage window was 2.8V~3.65V. The test results at 25℃ are shown in Table 1, and the test results at 45℃ are shown in Table 2.

[0133] Table 1. Performance test results of each test case at 25℃

[0134]

[0135] Table 2 Performance test results of each test case at 45℃

[0136]

[0137] Depend on Figure 1 visible, Figure 1The images show the XRD patterns of the polyvinylidene fluoride-hexafluoropropylene copolymer of Example 1.1 of this application and the polyvinylidene fluoride-hexafluoropropylene copolymer modified with ionic liquid. The specific ionic liquid can effectively transform the γ phase (T3GT3G') of the polyvinylidene fluoride segments into the highly polar β phase (TTT).

[0138] As can be seen from Tables 1 and 2, the composite electrode obtained by the preparation method of this application, when combined with the gel solid electrolyte, can achieve better capacity performance and long-cycle capacity retention, especially under higher temperature conditions, where the difference is significant. This indicates that the composite electrode obtained by the preparation method of this application can be in close contact with the solid electrolyte interface and form a stable interface structure.

[0139] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0140] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a composite electrode, characterized in that, Includes the following steps: An active layer is prepared by coating at least one side of a current collector with a slurry containing ionic liquid, polymer, active material, and conductive agent. The polymer contains vinylidene fluoride segments, and the ionic liquid includes one or more of imidazole bis(trifluoromethylsulfonyl)imide and pyrrolidine-onium bis(fluorosulfonyl)imide; In the slurry, the mass ratio of the ionic liquid to the polymer is 3:(1~4).

2. The method for preparing the composite electrode according to claim 1, characterized in that, The ionic liquid comprises one or more of the following: 1-ethyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide, 1-methyl-1-propylpyrrolidineonium bis(fluorosulfonyl)imide, 1-ethyl-1-methylpyrrolidineonium bis(fluorosulfonyl)imide, 1-propyl-1-methylpyrrolidineonium bis(fluorosulfonyl)imide, and 1-butyl-1-methylpyrrolidineonium bis(fluorosulfonyl)imide; and / or The polymer includes one or more of polyvinylidene fluoride homopolymer and polyvinylidene fluoride-hexafluoropropylene copolymer, wherein the molecular weight of the first polymer is 400,000 to 600,000.

3. The method for preparing the composite electrode according to claim 1 or 2, characterized in that, The composite electrode is a composite positive electrode, and the thickness of the active layer of the composite positive electrode is 10μm~70μm.

4. The method for preparing the composite electrode according to claim 3, characterized in that, The active material of the composite positive electrode includes one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium nickel oxide, and lithium cobalt oxide; and / or The conductive agent of the composite positive electrode sheet includes carbon nanotubes, the average tube length of which is 5μm~10μm and the average tube diameter is 7μm~15μm. and / or The mass ratio of the active material to the conductive agent is 90:10 to 99.5:0.

5.

5. The method for preparing the composite electrode according to claim 1 or 2, characterized in that, The composite electrode is a composite negative electrode; the thickness of the active layer of the composite negative electrode is 10μm~60μm.

6. The method for preparing the composite electrode according to claim 5, characterized in that, The active material of the composite negative electrode sheet includes one or more of graphite, lithium titanate, and hard carbon; and / or The conductive agent in the composite negative electrode sheet includes conductive carbon black, wherein the resistivity of the conductive carbon black powder is ≤0.25Ω·cm; and / or The mass ratio of the active material to the conductive agent is 95:5 to 99.5:0.

5.

7. A battery, characterized in that, The device includes a positive electrode, a negative electrode, and an electrolyte membrane, wherein the electrolyte membrane is disposed between the positive electrode and the negative electrode; the positive electrode includes a composite electrode sheet prepared by the preparation method according to any one of claims 1 to 4; and / or, the negative electrode includes a composite electrode sheet prepared by the preparation method according to any one of claims 1, 2, 5, and 6.

8. The battery according to claim 7, characterized in that, The electrolyte membrane includes a gel solid electrolyte membrane.

9. The battery according to claim 8, characterized in that, The gel solid electrolyte membrane includes a diaphragm impregnated with an electrolyte composite liquid, the electrolyte composite liquid including a second ionic liquid and a lithium salt; the second ionic liquid includes one or more of pyrrolidineonium-based ionic liquids and imidazolium-based ionic liquids.

10. An electrical appliance, characterized in that, Includes the battery as described in any one of claims 7 to 9.

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